polymerization anionic

HIGHLIGHT

Experimental Techniques in High-Vacuum AnionicPolymerization

DAVID UHRIG,1 JIMMY W. MAYS1,21Chemical Sciences Division and Center for Nanophase Materials Sciences,Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831

2Department of Chemistry, 655 Buehler Hall, University of Tennessee, Knoxville,Tennessee 37996

Received 3 March 2005; accepted 16 July 2005DOI: 10.1002/pola.21016Published online in Wiley InterScience (www.interscience.wiley.com).

INTRODUCTION

The high-vacuum technique employed in classical

anionic polymerization methodology requires highly de-

veloped and specialized skills. The polymer scientist

must possess both an adept glassblowing ability and a

thorough understanding of the behavior of compounds,

volatile and nonvolatile, in a vacuum environment. Clas-

sic reviews of these techniques that remain relevant

today were written by Fetters1 and by Morton and

Fetters.2 Hadjichristidis et al.3 published a more recent

technical review that very well captures many of the

advances made within this synthetic discipline over the

last 20 years and contains excellent descriptions of

the basic high-vacuum procedures, reagent preparation

and purification, polymerization techniques, and some

details on the synthesis of complex architectures using

anionic polymerization.

ABSTRACT: Experimental me-

thods used in high-vacuum anionic

polymerization are described in

detail, with extensive illustrations

to demonstrate proper procedures

and techniques. These descriptions

include construction and operation

of the vacuum line, handling purifi-

cation chemicals, ampulization tech-

niques, short-path distillations, ini-

tiator synthesis, polymerization pro-

cedures, and linking reactions using

chlorosilanes. A primary emphasis

is placed on safety. We believe

that this review of these methods

will be useful to scientists work-

ing in the field of anionic poly-

merization and may also benefit

other researchers in performing

tasks requiring ultra-high-purity

reaction conditions. VVC 2005 Wiley

Periodicals, Inc. J Polym Sci Part A: Polym

Chem 43: 6179–6222, 2005

Keywords: anionic polymeriza-

tion; break-seal; chlorosilane; glass-

blowing; high-vacuum line; orga-

nolithium reagent

Correspondence to: D. Uhrig (E-mail: [email protected])

Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 43, 6179–6222 (2005)

VVC 2005 Wiley Periodicals, Inc.

6179

Controlled anionic polymerization is a unique syn-

thetic means toward a large range of model linear and

branched polymers and copolymers.4–7 Very recently,

much new and interesting work has been accomplished.

Hogen-Esch and coworkers prepared macrocyclic poly-

mers through the strategy of (1) difunctional initiation of

a monomer and (2) coupling the resultant macromolecu-

lar dinucleophiles with dielectrophiles under conditions

of high dilution. Specifically, macrocyclic polystyrene

(PS) was prepared from either metallo-naphthalide or bis

(benzylide) initiation, and the resultant LiPSLi or KPSK

dianions were coupled into either methylene bromide or

1,4-bis(bromomethyl)benzene.8 In a similar manner, macro-

cyclic vinyl aromatic polymers [viz., both poly(2-vinyl-

naphthalene) and poly(2-vinyl-9,9-dimethylfluorene)] were

prepared with the same strategy.9

Pitsikalis and coworkers synthesized block copoly-

mers of styrene and either stearyl methacrylate10 or

decyl methacrylate.11 Vazaios and coworkers12 prepared

triblock copolymers and pentablock terpolymers of n-hexyl isocyanate with styrene and/or isoprene. These

polymers were prepared through sodium naphthalide ini-

tiation, sequential addition of monomers, and addition of

sodium tetraphenylborate to prevent unwanted back-bit-

ing during polymerization of the isocyanate.

Linear tetrablock quaterpolymers of styrene, iso-

prene, dimethylsiloxane, and 2-vinylpyridine were pre-

pared by Fragouli and coworkers.13 This multiblock

copolymer synthesis was accomplished through inde-

pendent asymmetric sequential polymerizations of the

four monomers, the intermediate products of which were

sequentially linked into a heterobifunctional linking

agent bearing one chlorosilyl functionality and one ben-

zylic chloromethyl functionality.

Dumas and coworkers14 prepared star block terpoly-

mers of styrene, tert-butyl methacrylate, and ethylene

oxide. This synthesis was accomplished by using an

approach based on 1,1-diphenylethylene (DPE); polystyr-

yllithium (PSLi) was end-capped with a siloxy-protected

DPE compound, and the resultant heterobifunctional

macroinitiator was then used to polymerize ethylene

oxide and tert-butyl methacrylate, in turn. In another set

of DPE-based synthetic experiments, Higashihara and

Hirao15 prepared asymmetric star polymers of three or

four different compositional segments. With the com-

pound 1,1-bis(3-chloromethylphenyl)ethylene and a

variety of polymerization and linking sequences, star

polymers were made from styrene, isoprene, 4-(trime-

thylsilyl)styrene, and 4-methoxystyrene.

Quirk and coworkers exploited anionic polymeriza-

tion as a means of end functionalization. In one such

report, polyisoprenyllithium (PILi) and polybutadienyl-

lithium ( PBLi) were cleanly functionalized with a ter-

minal hydroxy group by end capping with formalde-

hyde.16 In a separate set of experiments, polymeric orga-

nolithium compounds were derived to make diene-

functionalized macromonomers; in this synthesis, the

macromolecular organolithium species were end-capped

with 3,4-epoxy-1-butene, with subsequent dehydration

chemistry yielding the macromonomers.17

Contrastingly, as the new chemistry discoveries prog-

ress rapidly, the high-vacuum techniques themselves

remain, in many instances, nearly timeless. It is there-

fore worthwhile that we present this article, intended as

a companion work to the aforementioned earlier techni-

cal reviews, which provides additional and more detailed

information on exactly how to conduct essential manipu-

lations—to make such tasks more technically accessible

to scientists wishing to successfully accomplish them.

The extensive sketches within the text are designed to

aid in implementation of the written descriptions. A pri-

mary emphasis is placed on safety. In addition to this

consideration, the ability to work with chemicals under a

high-vacuum environment and maintain such a system

with integrity is the chief objective. The article has been

necessarily written in a decidedly tutorial tone through-

out. It is believed that this work will be especially useful

to scientists that are entering this field, ‘‘hands on’’ so to

speak; however, the methods are organized and intro-

duced with respect to technique, so more experienced

workers can proceed directly to a technique of interest.

Outline of Contents

The High-Vacuum LineConstruction 6181

General Safety Considerations 6181

Cleanliness and Working Efficiency 6183

Fundamental Techniques

Use of Tesla Coil 6184

Degassing 6184

Simple Distillation Techniques 6185

Purified Solvent Storage 6186

Purification Chemicals

Handling Chemicals Safely 6187

Transferring Organometallic Solutions 6188

Preparation of Liquid Potassium–Sodium

Alloy 6189

Preparation of Alkali Mirror 6190

Ampulization Techniques

Simple Ampulization 6190

Large-Scale Ampulization 6191

Dilution 6192

Freeze Ampulization 6192

Short-Path Distillation

Short-Path Apparatuses 6194

Portable Manifold 6196

Coerced Distillation 6196

Advanced Distillation Apparatuses 6198

6180 J. POLYM. SCI. PART A: POLYM. CHEM.: VOL. 43 (2005)

HIGH-VACUUM LINE

Construction

Two pumps working in series, such as depicted in

Figure 1, allow the attainment of a very high vacuum.

The pressure in the working high-vacuum manifold can

be several orders of magnitude lower than the lowest

pressure achievable by the mechanical pump alone. In

the 1700s, Bernoulli understood that particles in flow

exert a lower transverse pressure than particles in a sta-

tionary state. Today, by exploiting this same principle

that gives an airplane wing its lift or that allows a simple

laboratory water aspirator to provide a modest suction,

the diffusion pump can entrain gaseous particles and

direct them toward a mechanical pump. The diffusion

pump sets up a stream of vapor (the diffusion pump

fluid). As gases diffuse from the vacuum line into the

body of the diffusion pump, they are not rebounded in

the same way as from the walls of the glass manifold

elsewhere. Rather, here they encounter the stream of dif-

fusion pump fluid, in its vapor state and in a motion that

is away from the manifold. Thus, gases are swept toward

the mechanical pump and prohibited from returning.

The diffusion pump fluid itself has a high enough boiling

point that it may be contained and continuously recycled

through cleverly located condensers. (In a purely tutorial

note, the principle of the vacuum mechanism is quite

easily understood through the use of a metaphor on a

much more macroscopic level: a fish has greater diffi-

culty swimming upstream than downstream in a swift

current. Here then is a molecular case in which gas mol-

ecules face an analogous obstacle.)

The entire vacuum system is constructed from glass

and mounted securely to a stainless steel frame. We have

had reasonable success with the employment of high-

vacuum stopcocks constructed of a glass channel and

Teflon piston; the seal between the upper glass barrel of

the stopcock and the piston is made by an o-ring, itself

sheathed with Teflon, which may be very lightly greased

for both seal and lubrication. The working manifold is

approximately 1.5–2 m long because it becomes more

awkward to work if the vacuum ports are spaced more

closely than 30 cm apart. Apparatuses and flasks are

docked to the vacuum line through the use of comple-

mentary ground glass fittings and high-vacuum grease.

General Safety Considerations

Diffusion Pump

The diffusion pump fluid of choice, historically, has been

mercury, and we have traditionally used mercury diffusion

pumps ourselves. (Mercury is a heavy metal; therefore, a

stream of its vapor has a large momentum that is desirable

in an application such as this. Moreover, mercury does not

have a high affinity for organic compounds that may be

allowed to sweep through the pump.) However, because

of the health risks of mercury, we are currently striving to

methodically replace them with less hazardous options.

We have learned through practice that oil-based diffusion

pumps can work just as effectively, and we are presently

running trials of two different geometries of glass diffu-

sion pumps, both of which allow access to their interior,

thus permitting the changing of oil as needed.

Glassblowing repairs to the vacuum line must never be

attempted in the region of the diffusion pump while the

pump is hot; after it has cooled, blowing must never be

provided from the mouth. A hand-held T tube may be

used, which has a lightly pressurized inlet of nonflammable

gas (compressed air or nitrogen), an exit plumbed to the

system being blown upon, and a side valve that is opened

or closed easily with the use of the blower’s thumb.

If mercury is selected, then containment of the mer-

cury is essential. It should be kept in mind that there are

actually quite a few different geometries of mercury dis-

tillation pumps, and it is important to select one with

good condensers. Often it is desirable to add an extra

condenser to the exit (high-pressure side) of the diffu-

sion pump to help prevent the sweeping of mercury from

the pump. A surrounding catch pan, able to withstand

the temperature of the hot mercury in the event of a

breakage, is also a good idea. The traps must be vigi-

lantly filled, with liquid nitrogen on the low-pressure

Outline of Contents (Continued)

Synthesis of Organolithium Reagents, In Vacuosec-BuLi Synthesis 6199

DLI Synthesis 6203

sec-BuOLi Synthesis 6204

Polymerization Procedures in Nonpolar Solvents

Simple Technique 6206

Purge Technique 6207

Delayed Ampulization 6208

Canadian Technique in Detail 6209

Polymerization Procedures in THF

Simple Technique 6211

Polymerization of (Meth)acrylates 6214

Purge Technique 6215

Linking Manipulations Using Chlorosilanes:

Hellenic Technique in Detail 6215

Assembly of the Reactor to Flasks

of Collected Active Polymer 6216

End-Capping the Active Polymer with

Excess Chlorosilane 6217

Removing Excess Chlorosilane 6218

Titration of the Active Polymer into

Stoichiometric Chlorosilane 6220

Final Linking Manipulations 6221

HIGHLIGHT 6181

side and dry ice on the high-pressure side, for the mer-

cury to be safely isolated from the working vacuum

manifold and the mechanical pump and the synthesist

himself. The diffusion pump must never be heated if the

stopcocks isolating the pump are closed for a long

period, the mechanical pump is closed, or there is a dan-

ger of the water condensers being closed. The risk is that

the mercury can become superheated, in which case a

sudden decrease in pressure or opening of water flow

would lead to a potentially catastrophic event.

For the sake of completeness, realize that it is possi-

ble to obviate the diffusion pumping system altogether.

A turbo molecular pump is able to deliver the same vac-

uum capability. Under the best circumstances, this type

of pump could be considered the safest option. Never-

theless, such pumping units are exceedingly delicate and

do not suffer careless use (e.g., accidental in-streaming

of gas) without great expense. Furthermore, contamina-

tion with chlorosilanes, commonly used in anionic poly-

merization, can severely damage these pumps. For these

reasons, we do not use turbo molecular units ourselves.

Use of Clamps

The vacuum line must be clamped securely to the steel

frame. Clamps should be used generously around all pla-

ces where a force may be applied to the vacuum line:

traps, vacuum ports, and stopcocks.

It is necessary to clamp all flasks and apparatuses that

are docked to the line. Many accidents can be avoided if

the synthesist keeps the following simple but often over-

looked wisdom in mind at all times: vacuum is not a

force. If the sum of an object’s weight and its internal

pressure exceeds the net atmospheric force pushing it

up into the vacuum dock at any instant, then it will fall

if it is not clamped and will shatter if made of glass,

releasing dangerous chemicals into the laboratory envi-

ronment.

Internal Pressures of Closed Systems

Keep in mind also that the vacuum line is not designed

to withstand internal pressures greater than the surround-

ing atmosphere. All compounds must be kept below the

temperature at which they would boil under ambient

conditions, at all times. Gaseous monomers such as

butadiene are best collected, off the vacuum line, to a

chilled flask in the hood; subsequent transfer to the

vacuum line, with an appropriate cold bath already pre-

pared, is then safer.

When chilling flasks and traps with liquid nitrogen,

do not allow them to remain open to the atmosphere for

an extended period (of even several minutes) and then

close them. Oxygen can condense inside the container:

the result is potentially explosive.

In some procedures, it is necessary to provide a flow

of inert gas to the vacuum manifold. A twin bubbler

Figure 1. High-vacuum line.


such as that depicted in Figure 2 works very well. Inert

gas may be fed through the top and delivered to the vac-

uum line through one of the bubblers. The second bub-

bler provides a vent to the room. The flow of gas is

easily monitored as the stopcock to the vacuum line is

carefully opened.

Cleanliness and Working Efficiency

The vacuum line must be kept clean or its efficiency is

greatly compromised. The result of a messy vacuum line is

at best a waste of time in waiting for desired vacuum levels

to be achieved and at worst a compromise to the integrity

of all synthetic experiments conducted through its use.

The mechanical pump must be strong and in good

working order and should have its oil changed once per

month when the vacuum line is in daily use. If it is sus-

pected that a reactive compound has been permitted into

the pump (e.g., a monomer or chlorosilane), then the

pump oil must be changed immediately. Also realize

that if there is mercury in the mechanical pump, then

there is mercury in the room.

The vacuum manifold should be kept free of dust and

grease because these materials will simply attract and

cling to anything that is being distilled through the vac-

uum line. Once in a while, it is wise to clean the entire

manifold. To open the line and allow it to soak is the

easiest and first approach. Aqueous alkali solutions tend

to work well at dissolving small quantities of silicone

grease. Solvents such as tetrahydrofuran (THF) are also

useful for most organic compounds.

A more drastic, but once in a while necessary,

approach is the use of HF. It is recommended that this

be done only by two persons working together; more-

over, this method should not be attempted by someone

inexperienced or uncomfortable with the use of HF

because its misuse is life-threatening. It is, however, one

of the most effective methods of cleaning intricate glass-

ware. The vacuum manifold should be cut free from the

upper glass plumbing and taken to a well-ventilated lo-

cation where there is running water available. There it

may be rinsed carefully with HF by the first person while

the second person keeps water running continuously

over the first person’s hands and the outside of the mani-

fold. The manifold must be well rinsed and should be

allowed to air-dry for 1 day before any glassblowing

reassembly is performed.

Because it is so difficult to clean the vacuum mani-

fold, the best method is to keep it clean. Use short-path-

distillation techniques. It is possible to use a portable

liquid-nitrogen trap in some cases, below at the vacuum

port, to trap things before they can enter the manifold. It

is recommended that the vacuum manifold be allowed to

continuously pump for 24 h after work with monomers

or other compounds of low volatility.

Calcium hydride must be used to dry most materials;

however, when it is employed to dry large quantities of

hydrocarbon solvent (several hundred milliliters of ben-

zene or hexanes at a time), our recommendation is to dis-

till the solvent off the vacuum line (conventionally) and

simply keep it capped until it is needed. Then it may be

degassed over the subsequent chemical treatments. These

solvents are not appreciably hygroscopic, and large-scale

distillations are very difficult to accomplish without CaH2

dust being swept into the vacuum manifold.

The use of splashguards is optional over solvent reser-

voirs (see Fig. 3). Whether or not they are used, it is best to

avoid bumping solvent out of the reservoirs. It is usually

very difficult to avoid bumping solvents into the vacuum

Figure 3. Splashguard used to keep the main vacuummanifold clean.

Figure 2. Bubbler for safely pressurizing the vac-uum manifold.

HIGHLIGHT 6183

line if the reservoirs are more than half full, so it is wise to

use a vessel with a capacity well exceeding the needed

amount of solvent. Stir the reservoirs briskly and open the

stopcocks slowly to see how the solutions will behave.

FUNDAMENTAL TECHNIQUES

Use of Tesla Coil

The Tesla coil is a very convenient tool for checking the

level of the vacuum in the vacuum line. The Tesla coil is

noisy when held near or touching a vacuum manifold at

a pressure achieved by the mechanical pump (see Fig. 4,

point A). If the diffusion pump is working well, the coil

becomes silent on the high-vacuum side of the diffusion

pump (point B). Opening a system to the vacuum line

allows gases and volatile compounds into the vacuum

manifold. The Tesla coil is thus noisy upon the opening

of a new system to the vacuum line and becomes quiet

as molecules are pumped out of the line by the diffusion

pump. It is possible to distinguish whether they are gases

or volatile organic compounds by listening to the quality

of the vacuum on both sides of the liquid-nitrogen trap.

Gas molecules pass through the trap and are thus evi-

denced by noise from the Tesla coil on both sides of the

trap (B and C). Solvent molecules, contrarily, are cap-

tured there and produce noise only in the vacuum line on

the near side of the trap (C).

Degassing

A liquid system is degassed on the high-vacuum line

through an iterative sequence in which dissolved gases

Figure 4. Locations at which the pressure can be checked inside the vacuum line.

Figure 5. Illustration of a simple distillation (see the text for explanations).


are repeatedly permitted the opportunity to exit the sys-

tem. A round-bottom flask is attached to the vacuum

line, and the stopcock is opened to the vacuum for a few

seconds until the liquid begins to bubble, at which point

the stopcock is closed. The following sequence is now

repeated: (1) freeze the liquid, (2) open the stopcock to

the vacuum line for a couple of minutes, (3) close the

stopcock, and (4) thaw the liquid and stir it briskly for a

couple of minutes. Each time the liquid is refrozen, the

equilibrium is shifted so that dissolved gases may escape

and be removed by the vacuum pump.

A system being degassed is commonly pumped in the

frozen state until the Tesla coil is silent on the far side of

the liquid-nitrogen trap, at which point the stopcock is

closed and the liquid is thawed and stirred to adjust the

equilibrium. A system may be judged to be well de-

gassed if, at the first moment of opening the equilibrated

system to the vacuum pump, there is no noise from the

Tesla coil at point B.

Simple Distillation Techniques

With ambient gases out of the way, the remaining

atmosphere over a liquid in a closed high-vacuum sys-

tem is simply the vapor pressure of the liquid itself. By

the chilling of the destination to which the solvent must

be collected, the pressure is reduced there, and the sol-

vent travels from the source to the destination without

condensation ever occurring in the manifold.

Generally, liquids that boil below 100 8C under ambi-

ent conditions are distilled easily at room temperature

with the high-vacuum manifold. Solvents that are less

volatile may still be collected through the vacuum mani-

fold, but it is usually best to distill only to an adjacent

vacuum port.

An illustration is given in Figure 5. Here a source flask

is degassed, and stopcock E is closed. A destination flask

is evacuated by the opening of stopcocks D and F until a

high vacuum is achieved. D is closed. The destination

flask is supplied with a cold bath (conveniently �78 or

�196 8C), and the source is supplied with a room-tempera-

ture bath and stirrer. E is carefully opened. The liquid is

collected to the destination. During the distillation, it is

often necessary to supply heat to the source; the desirable

condition is to keep it at room temperature but not let it

become warmer than the vacuum manifold or else conden-

sation will occur throughout the vacuum line. After the dis-

tillation, E is closed. The destination is allowed a few

minutes to become cold and then is degassed by the open-

ing of D. Finally, F is closed, and the frozen liquid is

thawed and stirred.

If the source is not already well degassed, degassing

may be accomplished during the beginning of the distil-

lation procedure without the source being frozen. A very

Figure 6. Solvent-holding vessel.

Figure 7. Reservoir for the long-term storage of sol-vents.

HIGHLIGHT 6185

small quantity of liquid is collected to the destination by

boiling for 5–20 s, and E is closed. The liquid in the des-

tination flask is frozen, and the system outside the source

(that region to which the gases will be driven) is

degassed by the opening of D. When a good vacuum is

achieved (Fig. 4, check point B with the Tesla coil), D is

closed, and the distillation is resumed. By the repetition

of this iteration several times, a large quantity of liquid

is easily degassed without any need of freezing it at the

source. When the system is silent according to the Tesla

coil at point B, upon the first opening of D, the distilla-

tion may be allowed to progress without interruption.

The use of CaH2 is attended by the evolution of gas

so that even if the system has been degassed earlier, it

will likely be necessary to temporarily halt the distilla-

tion of a large quantity of solvent from CaH2 and degas

the system to maintain a high distillation rate.

Purified Solvent Storage

Solvents are stored at a vacuum port for up to several

weeks with a seal of high-vacuum grease. A cylinder such

as the one shown in Figure 6 is very convenient because

it can be calibrated; therefore, known amounts of solvent

are out-distilled with good accuracy. The bottom of the

cylinder must be slightly rounded for safe use at reduced

pressure. Generally, the greased vacuum joint will last

with integrity for 1–3 weeks, depending on the nature of

the solvent. Optionally, a room-temperature water dish

may be placed outside the cylinder for long periods of

waiting; through the simple evaporative action of the

water, the solvent inside the reservoir can be kept a

degree or so cooler than the vacuum manifold (and the

greased union), with the effect of retarding solvent mi-

grating into the grease and compromising the seal.

Alternatively, a specialty cylinder may be fashioned

such as the one shown in Figure 7. The glass side tube

allows the introduction of purification chemicals and is

subsequently sealed. Because this cylinder is fitted with

a stopcock of its own, it may be safely removed from the

vacuum port without risk to the integrity of the contents.

The grease is then easily refreshed or space is freed for

the establishment of an alternative working system upon

the manifold.

Several points are important in the use of large reser-

voirs of solvent. First, vacuum distillation does not

behave at all as a conventional distillation. In a conven-

tional distillation, the source is heated steadily until its

pressure finally exceeds the atmosphere above it; the

molecules at the lower surface of the reservoir are sup-

plied with energy, and the bubbles therefore form there:

the distillation is easily controlled. In a distillation at the

vacuum line, the pressure in the system is rapidly

reduced and remains somewhat fluctuant in nature. The

result is that bubbles form suddenly and anywhere in the

reservoir; solvent is easily bumped and splashed into the

vacuum line. This is undesirable because, although the

solvent is volatile and easily removed, the chemical

purification reagents are not. The reservoirs should not

be filled more than half full, and they must be stirred

briskly and opened to the vacuum manifold very care-

fully to see how the solutions will behave.

Vacuum distillations must be carefully tended. Often,

changes in temperature of the source have a great effect

on the rate of distillation, and the destination must be

regularly replenished with either liquid nitrogen or dry

ice. Often, doing several things at once means that the

distillation will take several times as long; hence, no

time is saved.

Finally, the thawing of a frozen liquid in a reservoir

is quite dangerous because there is a potential for the

flask to break. There is, of course, a change in density

associated with any freeze/thaw process. An empty bath

may be set to house the reservoir, and tepid water may

be poured, in one single addition, over the entire flask so

that the contents are freed from the surface of the glass

from the top down. If water is added too slowly or added

only to the bottom of the reservoir, it is much more

likely that a rupture of the flask will occur.

Figure 8. Handling organometallic solutions: step I.

Figure 9. Handling organometallic solutions: step II.


PURIFICATION CHEMICALS

Handling Chemicals Safely

Calcium Hydride

This is the most commonly used drying agent employed.

It is obtained in lumps and is best ground into a fine

powder just before use because it readily reacts with

moisture in the air. It can often be reused several times,

especially in cases in which it is used to treat nonhygro-

scopic solvents and in systems that are kept closed from

the atmosphere.

The leftover CaH2 is deactivated with water before

its disposal, but the reaction is too violent to simply add

water to the chemical. One method is to pour the chemi-

cal over ice. Another method is to make a slurry of the

powder in alcohol (e.g., ethanol) and carefully add water

(or dilute aqueous HCl) dropwise. Either of these deacti-

vation methods is still quite vigorous, is accompanied by

the evolution of flammable hydrogen gas, and should be

accomplished in the hood. Because the reaction with

CaH2 is heterogeneous, the deactivation is most safely

accomplished with stirring.

Sodium

This reagent is the most commonly used alkali in anionic

polymerization purification procedures. It is obtained in

large solid sticks and stored in grease-sealed desiccators.

It may be cut into small pieces in the room atmosphere

with a blunt stainless steel knife. It quickly builds up a

coating of oxide, so it should be protected from exposure

to the air for periods longer than 1 min. In cases in which

sodium without a coating of oxide is desired, the metal

may be cut under a blanket of hexane in a glass dish and

allowed to dry under vacuum or in an inert gas flow.

Leftover sodium is quenched by its reaction with

alcohol in the hood. Hydrogen gas is evolved. The reac-

tion with methanol is dangerous unless the metal is

already under another organic medium that will dilute

the methanol. Isopropyl alcohol is a safer choice. Again,

the reaction is heterogeneous, and it may be necessary to

stir the solution to ensure that the deactivation is safely

accomplished.

Potassium

This alkali metal is also somewhat regularly used and

requires even more care than sodium. It is received as

chunks under a blanket of mineral oil. The oil may be

removed by rinsing the metal with hexane, and it may

then be stored in a tightly capped jar under hexane; it is

strongly urged that the hexane should be first distilled

from CaH2 before use in this manner. Potassium must

never be allowed to dry in the room atmosphere. It will

spontaneously ignite in the presence of air. It reacts

explosively with both water and alcohol.

Leftover potassium must always be blanketed with a

large quantity of hexane (or, for periods of longer stor-

age, heptane, which has the benefit of being less vola-

tile), and unused material may be quenched in the hood

by the careful dropwise addition of alcohol to the hexane

solution.

Lithium

Lithium is used primarily in the synthesis of organo-

lithium reagents and should consequently be kept clean

as possible. We have had good success in the use of a

dry powder or granular form that contains �0.5% Na. It

is best to open, handle, and transfer the metal only under

a continuous blanket of inert gas. Nitrogen is adequate,

but argon is a better choice.

Figure 10. Handling organometallic solutions: stepIII.

Figure 11. Handling organometallic solutions: step IV.

HIGHLIGHT 6187

Excess lithium is extremely reactive when it is in a

powder form. It may be quenched in a manner similar to

that of potassium.

Organometallics

Butyllithium (BuLi), dibutylmagnesium (Bu2Mg), and

alkylaluminums (Alk3Al) are received as hydrocarbon

solutions in bottles protected with a sureseal cap. They

are obtained from the bottles by using needle-transfer

techniques in one of two ways. In the first method, a dry

needle-tipped syringe is filled with at least as much inert

gas as the amount of organometallic solution desired,

the septum is pierced, the inert gas is injected into the

bottle, and the solution is withdrawn. In the second

method, the bottle is pierced by a needle that is plumbed

to a flow of inert gas; with a needle-tipped syringe, the

septum is pierced a second time, and the solution is

withdrawn under the compensating pressure of inert gas

from the first needle.

The second method is the better technique. The han-

dling of such reagents is illustrated later in greater

detail.

The quenching of pyrophoric organometallic com-

pounds is extremely dangerous and should be accom-

plished in the hood, with the shield drawn. Concentrated

solutions may often not be quenched without the violent

attendance of fire; therefore, if the reagent is not already

diluted with leftover solvent or monomer, then it should

first be diluted with a small quantity of hexane. The drop-

wise addition of methanol is accompanied by the evolu-

tion of both heat and gaseous hydrocarbon (e.g., butane).

Transferring Organometallic Solutions

Organometallic reagents are routinely employed in the

course of anionic polymerization methodologies. BuLi,

Bu2Mg, and Alkyl3Al solutions are steadfastly protected

from the atmosphere with appropriate blanketing and

transfer techniques. Because they are extremely reactive

(pyrophoric), it must never be forgotten to handle them

with respect, for the sake of both the experimentalist’s

safety and the reagent’s potency. Although a thorough

familiarization with cannula techniques18 would indeed

greatly benefit the synthesist, this description is intended

only to narrowly illustrate the effective transfer of such

a compound to a vacuum system. A step-by-step account

is provided here and is illustrated in Figures 8–12.

I. The bottle of the reagent solution is kept in a bottle

equipped with a septum. When the reagent is needed,

the septum is pierced with a needle that can deliver a

light pressure of inert gas. A dry needle-tipped syringe is

then also inserted through the septum (Fig. 8).

II. The solution is drawn into the syringe. Tilting of the

bottle may be necessary (Fig. 9).

III. The flask or apparatus requiring the solution is

already prepared and dried and is under vacuum; the

stopcock to the vacuum manifold is now closed. The

solution is injected by piercing a rubber septum with

the needle of the syringe. Because the system is under

vacuum, the contents are spontaneously inhaled into the

flask (Fig. 10). Care should be taken to exclude as much

air as possible from the system: after the solution has

been drawn into the flask, the syringe is immediately

withdrawn from the septum; otherwise it will continue

to leak. A small quantity of grease may be applied to the

septum.

IV. The constriction of the side arm is rinsed free from

any residual organometallic compound. A towel strip

dipped in liquid nitrogen and briefly wrapped around

the side arm effects this: the blanketing solvent (e.g.,

hexane) refluxes quite easily from room temperature

because the system is under reduced pressure (Fig. 11).

In the event that a little air has been allowed into the sys-

tem through a clumsy transfer, the vacuum may often be

enhanced by the opening of the flask to the main vacuum

for 2 s. The constriction should be rinsed several times.

After the constriction is clean, it is sealed, and the side

arm is detached through the use of the hand torch.

Figure 12. Handling organometallic solutions: step V.

Figure 13. Preparation of the K/Na alloy: step I.


V. The stopcock to the vacuum manifold is now reop-

ened, and the solvent is stripped from the organometallic

reagent. It is often not necessary to remove all traces of

the solvent from the reagent as long as all gases have

been removed. The flask is now prepared for subsequent

in-distillation of the solvent or monomer to be thus treated

(Fig. 12).

Generally, the organometallic stock reagents are kept

in the refrigerator after opening. A glovebox is alterna-

tively appropriate. These reagents often become cloudy

after opening several times; however, their potency is

generally retained to be effective as purification agents.

(This can indeed be verified by the careful quenching of

the material after its use in the hood.)

Once the septum has been pierced the first time, it

begins to deteriorate slowly; thus, we can extend the life

of the reagent by insisting upon inert gas blanketing,

keeping the solution away from direct contact with the

septum, and also placing a small fresh piece of folded

parafilm over the septum (underneath the screw-on cap)

after each use. In this way, the reagent is preserved for

quite a long time and for repeated sampling.

Preparation of the Liquid Potassium–Sodium Alloy

The K/Na alloy is prepared in the laboratory. Because it is

an extremely powerful reducing agent, it must be pre-

pared, handled, and finally quenched with utmost care in a

manner similar to that previously described for the han-

dling of K metal. A step-by-step description of the prepa-

ration is given here and is illustrated in Figures 13–17.

I. A flask or apparatus is prepared from all-glass con-

struction and fitted with a glass exit/entry tube. The

apparatus is docked to the vacuum line, evacuated,

flame-dried, and checked for integrity by using the Tesla

coil. It is then repressurized with a blanket of inert gas

(Fig. 13).

II. K and Na metal are cut into small pieces under a

blanket of dry hexanes. The quantity of alkali metal used

is adjusted, according to the eye, so that the ratio of K to

Na is about 3. For the purpose of making the alloy, any

large accumulation of oxide coating is best cut off the

surface of the metals (Fig. 14).

III. Under a stream of inert gas delivered from the

opposite opening of the apparatus, K and Na are trans-

ferred to the flask (Fig. 15). The hexane is allowed to

evaporate from the metal under a slow flow of inert gas

for about 10 min.

IV. The apparatus is closed. The following series of

events must be accomplished in quick succession:

(1) the inert gas flow is stopped; (2) from a remote loca-

tion (preferably through the vacuum line, for a greater

distance), a blowpipe is fitted for use upon the apparatus;

(3) the glass tube is sealed and blown round (it is impor-

tant to not blow too much, but the entry needs to be

both sealed without a hole and stable to withstand out-

side atmospheric pressure); and (4) the apparatus is evac-

uated to the vacuum.

V. The flask is gently heated with a soft moving flame

from a hand torch (Fig. 16). K will melt before Na

melts. As soon as it can be seen that K is beginning to

melt, the heating is stopped.

VI. With a horseshoe countermagnet, the internal glass

stirring bar is moved about, agitating the metal contents

(Fig. 17). K finishes melting. Na also begins to melt and

is dissolved into the molten potassium. After all of the

solid chunks of metal have been incorporated by hand,

the horseshoe magnet may be removed and replaced by

a magnetic stirring plate.

Figure 14. Preparation of the K/Na alloy: step II.

Figure 15. Preparation of the K/Na alloy: step III.

HIGHLIGHT 6189

VII. The apparatus may be closed from the vacuum

line. The contents are stirred for about 1 h until a very

smooth, homogeneous alloy is formed. The alloy re-

mains a liquid at room temperature.

If the vessel to contain the alloy is fitted with a stop-

cock, we can instead introduce the solid pieces of K and

Na through the stopcock barrel, thereby avoiding the risk

of sealing and blowing the glass side arm, as directed

previously. Keep in mind that the K/Na alloy is poten-

tially one of the great fire dangers in the laboratory. The

previous description is essentially an account of how to

prepare the alloy; the decision of when to employ it is

left to the judgment of the experimentalist. A more

benign chemical substitute is diphenylhexyllithium (the

adduct of BuLi and DPE), which works well as a drying

agent for ethereal solvents.

Preparation of Alkali Mirrors

Alkali mirrors must be freshly prepared, under vacuum,

in the apparatuses requiring their use. Na mirrors are the

most common (although K mirrors can be just as easily

prepared). The main advantage of a mirror is that it has

an extremely large solid alkali surface area of very high

purity that cannot be otherwise obtained. A step-by-step

procedure is given here and aided by Figures 18–20.

I. A flask or apparatus is prepared from all-glass con-

struction and fitted with a glass exit/entry tube (see

Fig. 18). The apparatus is docked to the vacuum line,

evacuated, flame-dried, and checked for integrity by

using the Tesla coil. It is then repressurized, removed

from the vacuum line, inverted, and blanketed under a

flow of inert gas.

II. The alkali metal is introduced to the side tube under a

light flow of inert gas. If hexane is used as a blanket (man-

datory for K, optional for Na), then it must be allowed to

evaporate for several minutes under the stream of inert gas.

III. The apparatus is closed. The following series of

events must be accomplished in quick succession: (1)

the inert gas flow is stopped; (2) a blowpipe is fitted for

use upon the apparatus at the opposite end of the alkali

metal inlet; and (3) the glass tube is sealed and blown

round (it is important not to blow too much, but the entry

needs to be sealed and stable to outside pressure).

IV. As soon as the glass has cooled, the apparatus is

inverted back to its right-side-up orientation, docked to

the vacuum line, and evacuated. The apparatus is

pumped until a good vacuum is achieved (see Fig. 19).

V. The alkali metal and glass arm are heated with a

hand torch. The torch is adjusted to maintain a large, dif-

fuse blue flame. The torch is moved continually so that

the entire glass arm becomes very hot, and the alkali

metal is distilled under dynamic vacuum to the flask. It

is important to keep the torch moving because the flame

must be adjusted to a temperature at which the glass

would melt if it were held still.

VI. Optionally, the glass side arm is detached by seal-

ing the constriction nearest the flask. The reward is a

mirror coating the flask, with the appearance of a Christ-

mas ball (Fig. 20).

AMPULIZATION TECHNIQUES

Simple Ampulization

A volatile compound is distilled through the vacuum

manifold into ampules and captured by sealing the con-

Figure 16. Preparation of the K/Na alloy: step V.

Figure 17. Preparation of the K/Na alloy: step VI.


strictions with a hand torch. A basic all-glass ampuliza-

tion apparatus is shown in Figure 21. This type of appa-

ratus is useful for the collection of small quantities of

solvents such as Lewis additives or alcohols. Briefly, the

stepwise sequence to be used is as follows.

I. The apparatus is evacuated on the vacuum line and

verified for integrity by use of the Tesla coil. The

ampules are flame-dried and pumped until a high vac-

uum is persistent.

II. The compound is collected to the apparatus with a

simple distillation through the manifold. Because of the

geometry of the ampule, a cold bath cannot be used. Fol-

lowing are two convenient methods of chilling the

ampules: (1) with a small cloth towel strip dipped in

liquid nitrogen, the ampule is briefly cloaked and

chilled; or (2) with a small bath of dry ice and isopropyl

alcohol beneath the ampules, the ampules are bathed

with the slurry with a small brush, the drip-off below the

apparatus being caught with the bath.

III. The ampules are taken by being heat-sealed and

detached from the apparatus at the constrictions.

Naturally, as many or as few ampules as desired may

be assembled in an apparatus. Apparatuses tend to

become clumsy and easier to break if there are more

than 10 ampules. It is wise to not build an apparatus

larger than it needs to be. We can calibrate the ampules

by filling them with a known quantity of deionized water

and placing a scratch on the glass before assembling the

apparatus.

Besides the apparatus breaking because of gross

mechanical failure of the glass, there is another potential

reason for failure of the apparatus. If there is a small

quantity of moisture in the apparatus when it is first

opened to the vacuum line, sudden evaporation can

cause the water to freeze inside the break-seals and rup-

ture the seals. To remove much of the water, the appara-

tus can be dried in an oven at 120 8C. Otherwise, it iswise to warm at least the break-seals with a soft blue/

yellow flame of the torch and to keep them warm during

the initial evacuation of the apparatus.

In the sealing of constrictions, a sharp, focused blue

flame must be used. It is necessary to heat all sides of

the constriction equally or it will collapse asymmetri-

cally and possibly implode. If the back of the constric-

tion cannot be heated, then do not heat the front either;

deliver the heat tangentially left and right. Keep in mind

that heat rises. As the glass softens, pull the ampule gen-

tly to help the glass collapse uniformly. Back off with

the torch at the end and polish the seal for a few seconds

at a lower temperature.

Large-Scale Ampulization

It is sometimes necessary to ampulize a large quantity of

a compound for a single use. Alternatively, it may be

desirous to capture a reagent on a large scale so that

small, later decided quantities may be easily taken as

they are needed. An apparatus suitable for these types of

needs is shown in Figure 22.

This ampulization technique is particularly appropri-

ate if the purification of a compound is difficult and if it

is desired to purify an extra amount for easy later use. It

is also useful in the case of a reagent that, once opened,

is best captured and sealed under vacuum for reasons of

wishing to retain the integrity of the reagent.

Figure 18. Preparation of an alkali mirror: steps Iand II.

Figure 19. Preparation of an alkali mirror: step IV.

HIGHLIGHT 6191

For example, commercial organolithiums often lose

their potency once the seal is compromised the first time.

Transfer of the organolithium reagent into an all-glass

apparatus and degassing are wise if it is desired to use

the reagent repeatedly (for use as an initiator, for exam-

ple, where a quantitatively controlled portion is impor-

tant). The apparatus in Figure 22, as depicted, is suited

for an in-distillation of reagent through the vacuum

manifold, but a small constricted entry can easily be

added to the main flask (such as shown in Fig. 10). After

drying the ampulization apparatus, the concentrated

reagent may be injected. Optionally, the apparatus may

be first repressurized with inert gas, and a carefully con-

trolled long-needle delivery of the reagent may be made

to the flask.

Small bottles of chlorosilanes are also best purified

once they are opened. Otherwise, the rubber-lined caps

tend to degrade rapidly after they are pierced.

Dilution

A typical dilution apparatus is shown in Figure 23. With

an apparatus such as this, an ampule of a concentrated

reagent may be diluted with a solvent obtained from a puri-

fied reservoir elsewhere docked to the vacuum manifold.

The apparatus may be purged with BuLi by the

attachment of a purge section. Generally, purging is nec-

essary in the case of preparing dilute organolithium solu-

tions of concentration precision or in the dilution of mul-

tifunctional organolithiums. Otherwise, it is simply

advised to allow a long pumping time under the vacuum

and to flame-dry the apparatus repeatedly.

Silanization is an alternative to purging and is some-

times prudent in the use of multifunctional chlorosilanes.

When the chlorosilane is used in concentrated (excess)

amounts, it is expedient to simply use the apparatus.

When a chlorosilane must be repeatedly transferred to

additional apparatuses or diluted for stoichiometric

usage, it is best to first silanize the apparatus. (CH3)3SiCl

is the chlorosilane used for this purpose. Any impurities

that are deleterious to the Si��Cl bond, including glass

surface contaminants such as Si��OH, are given an

opportunity to deactivate with a small sacrificial quantity

of this silane. Experimentally, a small quantity of

(CH3)3SiCl is introduced to the apparatus and used to

completely wash the inner glass surface (liquid nitrogen/

towel strip); the contents are then pumped, without flame

drying the apparatus, until a good vacuum is achieved.

The apparatus is then ready to capture the chlorosilane

to be employed experimentally.

When ampules of the reagent are taken, it is first nec-

essary to rinse the constriction if the diluted reagent is

nonvolatile (e.g., organolithiums will not move out of

the way of the flame but rather will stay and decompose

on the surface of the glass). If the constriction is rinsed,

be aware that the concentration will be affected. Gently

back-distilling the amount of solvent used in rinsing to

the cylinder, before detaching the ampule, will ensure a

steady concentration in the apparatus. If the contents of

the apparatus are all volatile, simply prewarm the con-

striction gently with the torch to allow all reagents to

move out of the way before detaching the ampule.

Freeze Ampulization

An ampulization apparatus of alternative geometry,

depicted in Figure 24, permits the freezing of a volatile

Figure 20. Preparation of an alkali mirror: step VI.

Figure 21. Simple ampulization apparatus.


compound before it is detached and sealed into an

ampule. This technique is particularly advised in the col-

lection of monomers but can be used for the collection

of any volatile compound that is unstable in the presence

of heat.

A general stepwise experimental procedure is given

here.

I. The apparatus is evacuated on the vacuum line, and

the ampules are flame-dried and pumped until a high

vacuum is persistent.

II. The compound is collected to the apparatus by

the performance of a simple distillation through the

manifold. After the compound is collected into the

ampule, it may be thawed to measure the volume

collected; adjustments can be made by further in- or

out-distillation.

III. The source is closed. The ampule is frozen at

�196 8C, and the apparatus is opened to the main vac-

uum to permit a final degassing.

IV. The ampules are taken by being heat-sealed and

detached from the apparatus at the constrictions.

It is important to ampulize monomers in this way

both because they are unstable and because they must be

exceedingly pure to obtain high-molecular-weight poly-

mer. (The propagation step must occur many times un-

ambiguously.) It is advised to give the compounds

several minutes to become cold and to leave the main

vacuum open during the detachment of the ampules.

Moreover, after the ampule is sealed, the contents should

be kept frozen until all of the glass has cooled to room

temperature.

Thaw the ampules and let them come to rest at 20 8C(or whatever temperature is required for the density

value being used) before taking a volumetric measure-

ment. Otherwise, for long experimental periods, keep

them cold as necessary.

Volatile monomers (e.g., isoprene, bp ¼ 35 8C;cyclohexadiene, bp ¼ 80 8C) are easily collected

through the vacuum manifold.

Exceedingly volatile monomers (e.g., butadiene, bp

¼ �5 8C) may be ampulized; however, they must be

diluted in the ampule to reduce their pressure. The

monomer is collected and measured at a cold tempera-

ture at which a density value is available. Subsequently,

it is frozen, and the solvent is collected above the mono-

mer; the ampule is degassed, detached, cooled, and care-

fully thawed.

Freeze ampules may be constructed in several stages

of round tubing (see Fig. 25). This permits collection of

first a small quantity of one compound, with a reason-

Figure 22. Large-scale ampulization apparatus.

HIGHLIGHT 6193

able volumetric accuracy, and subsequently a large

amount of another compound. For example, in this way

both a monomer and the solvent required for its poly-

merization may be captured in one ampule. The proce-

dure to be followed in a compound freeze ampulization

is essentially the same as that described in a simple

freeze ampulization.

SHORT-PATH DISTILLATION

Short-Path Apparatuses

Compounds that have a low volatility (usually mono-

mers) can still be transported with distillation techniques

under vacuum. It is best to require them to travel only

short distances. Often they must be heated at least slightly

above room temperature to increase their vapor pressure;

this leads to a more global condensation behavior such as

is observed in conventional distillations. This behavior is

a good reason to restrict the distillation path as much as

possible. Specialized short-path apparatuses are extremely

useful. The following detailed procedure and the support- Figure 24. Freeze-ampulization apparatus.

Figure 23. Dilution apparatus.


ing illustrations given in Figures 26–28 describe a twofold

(two distillations and two apparatuses) purification.

I. An all-glass drying apparatus is prepared, evacuated,

dried, verified for integrity, and repressurized.

II. A Teflon stirring bar, CaH2, and the monomer are

introduced to the apparatus.

III. The entry tube is closed with a septum, the appara-

tus is redocked to the vacuum line, the contents of the

apparatus are frozen, the apparatus is evacuated, and the

entry tube is sealed with the torch.

IV. The contents are degassed, thawed, and allowed to

stir over CaH2.

V. The monomer is distilled to the preliminary am-

pule; a slightly warm water bath may be used at the flask

as necessary, but it is best to use no more heat than is

required. A brief degassing immediately beforehand

greatly helps to promote transport of the compound. The

ampule is frozen well and detached from the apparatus

with a hand torch.

VI. With the preliminary ampule collected from the

drying procedure, a final purification apparatus is as-

sembled. This apparatus is docked to the vacuum line,

evacuated, verified for integrity, and dried.

VII. The apparatus is closed from the manifold and left

under vacuum. Using the side-arm entry, a small quan-

tity of an organometallic solution is injected into the

apparatus with a syringe (e.g., the purification of styrene

requires the use of Bu2Mg).

VIII. By using a towel strip dipped in liquid nitrogen to

lightly reflux the solvent of the organolithium reagent,

the side arm is rinsed in the vicinity of the constriction;

the side arm is then sealed with the hand torch, and the

solvent is removed by reopening the apparatus to the

main vacuum. The apparatus is pumped until a good

Figure 25. Freeze ampulization: compound (dilu-tion) ampule.

Figure 26. Short-path distillation: drying apparatus.

HIGHLIGHT 6195

vacuum is achieved and the solvent has been removed to

the main liquid-nitrogen trap.

IX. The apparatus is closed from the manifold; the seal

to the preliminary ampule is ruptured; and the monomer

is collected to the flask, where it is frozen. The apparatus

is opened to the vacuum line and allowed a final degass-

ing; the empty preliminary ampule may be detached.

The monomer is thawed and allowed to stir over the

organometallic reagent.

X. The monomer is collected to the final ampules,

using freeze-ampulization techniques. Before the

ampules are detached, it is recommended that the entire

contents of the apparatus be frozen and the system be

opened to the main vacuum in preparation for use of the

torch.

Portable Manifold

It is possible to do less glassblowing and still keep high-

boiling compounds out of the permanent vacuum mani-

fold through the use of a portable manifold, which may

be easily cleaned and reused many times. Purification

flasks with complementary connections are needed, but

they are recyclable as well. A portable short manifold is

depicted in Figure 29.

This short cut is a quite viable option for compounds

that boil below �200 8C under ambient conditions.

Keep in mind that contamination of grease into the final

ampules must be prevented. The less volatile com-

pounds tend to behave much better through the employ-

ment of an all-glass path having as little a vertical climb

as practical.

Coerced Distillation

Distilling compounds that have an exceedingly modest

volatility can still be accomplished under high vacuum.

An all-glass path, a dynamic vacuum (open vacuum

during the distillation procedure), and the use of stron-

ger heat than in routine short-path distillations are

requisite; moreover, these compounds are nearly al-

ways purified in a manner that only requires one dis-

tillation to be performed. Compared with a conven-

tional procedure, which would ordinarily be attended

by a great loss of material due to side reactions or

decomposition, the boiling point is often diminished by

150–200 8C through the use of these techniques. A

step-by-step procedure is given presently and is sup-

ported by Figures 30–33.

I. The apparatus is assembled according to the illustra-

tion in Figure 30. After the apparatus is evacuated and

Figure 27. Addition of compounds to an all-glassapparatus.

Figure 28. Short-path distillation: final purification apparatus.


its integrity is established, it is repressurized with inert

gas by a feed through the vacuum manifold. A needle

through the septum provides a vent from the apparatus

after it has been pressurized.

II. The compound to be purified is introduced to the

apparatus through the side arm with a needle-tipped

syringe (see Fig. 31). The side arm is ideally constructed

of a short enough length that the needle can reach

through the constriction into the flask and thus facilitate

a clean delivery of the material.

III. With a clean needle and syringe, the purification

agent is added next, dropwise. For example, the purifica-

tion of DPE and similar compounds is accomplished by

the addition of a solution of n-BuLi in hexanes, drop-

wise, until a persistent vivid red metalation adduct is

formed. Note that the addition of reagents to the flask

would be uncontrollable if it were under vacuum. After

the reagents have been added, the needles are removed

from the septum and the inert gas feed is closed. The

introduction of a modest amount of vacuum (by the

momentary opening of the apparatus to the main vac-

uum) permits rinsing of the constriction (with a towel

strip dipped in liquid nitrogen) should rinsing be neces-

sary before the apparatus is sealed.

IV. The side arm is detached. The apparatus is care-

fully opened to the vacuum with brisk stirring; the vola-

Figure 29. Portable short-path manifold.

Figure 30. Coerced-distillation apparatus.

HIGHLIGHT 6197

tile solvent diluent of the organometallic agent is

stripped from the solution, and the remaining contents

are left to stir under dynamic vacuum for a period allow-

ing the purification to be accomplished.

V. The distillation is commenced by raising the tem-

perature of the flask; the vapor pressure of the compound

is increased to permit it to reflux in the flask. The

vacuum is left open during the procedure (see additional

notes at Fig. 32).

VI. After the distillation is complete, the flask is

allowed to cool. The flask and goose-necked distillation

path are detached from the apparatus.

VII. Purified solvent (hexanes) is distilled into the col-

lection cylinder from a reservoir elsewhere docked at

the vacuum manifold. This helps both to dilute the com-

pound and to decrease its viscosity. The apparatus is

detached from the vacuum line by sealing the opposite

constriction (see Fig. 33 to view the apparatus at this

point).

VIII. The contents are mixed well and split into the

ampules. The ampules are finally detached from the

remaining apparatus and stored for later use.

Advanced Distillation Apparatuses

The apparatuses depicted in Figures 34 and 35 require a

more adept glassblowing skill. The payoff of this extra

work is the ease with which distillations may be accom-

plished through their use. The distillations are directed

through an all-glass path, which obviates the risk of con-

tamination with vacuum grease; moreover, the com-

pounds are persistently excluded from the vacuum mani-

fold.

The experimental procedure to be followed during

the purification and ampulization of compounds with

these apparatuses is analogous to that previously de-

scribed for short-path distillation, and so a step-by-

step account of the technique is omitted. Figure 34

shows an apparatus intended to be useful for an ordinary

short-path style of distillation (i.e., the vacuum is closed

Figure 31. Addition of reagents to the apparatus.

Figure 32. Coerced distillation in progress.


during the distillation). After the calcium hydride and

the compound are collected into flask 1, it is sealed from

the room and degassed. Next, we seal the glass bridge

toward flask 2 with a torch by collapsing the capillary

and cutting it gently with a glass rod. Flask 2 is then pre-

pared with the organometallic reagent. At the appropri-

ate time, the seal between flasks 1 and 2 is ruptured (this

reopens the glass bridge), and the compound is collected

to flask 2; after the final chemical treatment, the com-

pound is collected to the ampules. For example, methyl

methacrylate can be treated first with CaH2 and then

with Oct3Al with this apparatus.

A twofold coerced distillation is accomplished with a

minimum of experimental difficulty with an apparatus

such as that depicted in Figure 35. A difficult compound

may thus be distilled twice under a dynamic vacuum.

For example, 4-(t-butyldimethylsilyloxy)styrene (a silyl-

protected para-hydroxystyrene monomer) can be treated

with CaH2 and Bu2Mg, sequentially, and finally diluted

in hexanes with this apparatus.

SYNTHESIS OF ORGANOLITHIUMREAGENTS IN VACUO

The quality of organolithium reagents is very crucial to

successful reproducible polymerizations. In some cases,

clean commercial products are available. We prefer to

synthesize the following compounds in house, and the

necessary manipulative techniques are illustrated through

the three specific synthetic examples chosen.

sec-BuLi Synthesis

This initiator is synthesized through the reduction of

sec-BuCl by Li metal according to the following chemi-

cal reaction:

sec-BuClþ 2Li�!sec-BuLiþ LiCl

This reaction is accomplished inside an all-glass syn-

thetic apparatus,19 which is shown in Figure 36. The

preparation of the synthesis requires previous ampuliza-

tion of sec-BuCl and purification of hexane. sec-BuCl is

Figure 33. Split-down abdomen of the all-glass ap-paratus.

Figure 34. Compound short-path-distillation apparatus.

HIGHLIGHT 6199

dried over CaH2 on the vacuum line with stirring over-

night, degassed, and ampulized (simple ampulization);

subsequently, this ampule is assembled to the vacuum

synthetic apparatus. Hexane is left on the vacuum line,

over BuLi, in a purified reservoir. Li metal (0.5% Na,

powder) is recommended in a quantity at least sixfoldthat of sec-BuCl. A convenient recipe uses 10 g Li,

20 mL sec-BuCl (the limiting reagent), and �200 mLhexanes.

The full synthesis is now described in a step-by-step

account, the text of which is supported pictorially by

Figures 36–39.

I. The apparatus is assembled, as shown in Figure 36,

and docked to the vacuum line. Because of the size of

the apparatus, the use of several clamps is advisable to

stabilize both the upper and lower portions. The appara-

tus is then evacuated, verified for integrity by use of the

Tesla coil, and flame-dried. The apparatus is then care-

fully repressurized with a blanket of inert gas.

II. The lithium is introduced into the apparatus by

means of the removable ampule (see Fig. 37). Depend-

ing on the physical state of the Li metal, it may be more

or less forgiving of the exposure to the room atmos-

phere. We have had good success in the past with a fine

dry Li powder, which must be carefully protected.

Recently, we have used more coarse granules (small, dry

chunks). Li dispersion in paraffin is rather tolerant of the

ambient atmosphere for short periods; however, it is

later experimentally laborious to strip the paraffin away,

by the washing with hexanes, and we therefore do not

recommend it.

III. After the ampule of Li metal is attached to the

apparatus, the inert gas is closed to the vacuum mani-

fold; the apparatus is carefully opened to the vacuum;

the Li powder will dance a little as the pressure is

reduced; and the apparatus is left to degas until a high

vacuum is achieved.

IV. BuLi is injected into the purge flask, the side arm

is rinsed and sealed, and the apparatus is degassed.

V. Hexane is in-distilled to the apparatus, and the

apparatus is again degassed.

VI. The following sequence is best accomplished

somewhat quickly if possible:

� The apparatus is detached from the vacuum

line.

� The hexane and BuLi are thawed.

� The apparatus is carefully tumbled in all direc-

tions to wash the entire inside glass surface and

the Li metal with the BuLi solution.

� Li powder is collected out of the ampule and

into the reactor, and the heavy wall glass path

between the reactor and the ampule is rinsed as

well as possible.

� The glass entry tube is sealed shut, and the

portable ampule appendage is removed from the

reactor.

The apparatus is now entirely sealed within glass, and

there should be no leaking.

Figure 35. Compound coerced-distillation apparatus.


VII. The apparatus is set in a position to reflux from

the purging recovery flask. The BuLi is thus rinsed from

the apparatus and collected back to the recovery flask

over a period of several hours. It will take time to collect

hexanes above the glass filter in each rinsing iteration,

but the reactor and Li must be rinsed well. The intermit-

tent use of a towel strip dipped in liquid nitrogen is help-

ful. Periodically collect all of the hexane back to the

recovery flask, by chilling the flask, to begin a fresh

rinse cycle.

VIII. Hexane is carefully distilled to the reactor, and

the purging section is detached from the apparatus.

IX. Li metal is collected as cleanly as possible to the

reactor flask (removed from the path to the sec-BuClampule). The reactor is inverted to a position such as

depicted in Figure 38.

X. The reactor is chilled to 0 8C, and the Li dispersion

is stirred briskly. (The reaction is exothermic and must

Figure 36. Vacuum synthetic apparatus for the synthesis of sec-BuLi.

HIGHLIGHT 6201

be controlled; moreover, the reaction product is not sta-

ble at room temperature for long periods.)

XI. The seal to sec-BuCl is ruptured; the contents are

allowed to gently distill to the reactor over the course of

�1 h. Once the contents have been distilled, the reactor

is continued with brisk stirring at 0 8C for 4 h. Finally,

the reactor bath is packed with ice, and the reaction is

left to complete overnight.

XII. The reactor is inverted, and the solution is col-

lected through the filter (see Fig. 39). A very clear, pale

yellow hue is observed. It is best to let the solution pass

very slowly through the filter, to avoid pulling any small

Li dust particles through the filter, and to pull the prod-

uct with the solvent. A cool water bath is both gentle

and safe to use (5–10 8C, keep the level of the bath

below the level of accumulating solution). It is not rec-

ommended to rinse the reactor; the solution is simply

allowed to collect below in one transfer.

XIII. The apparatus is rotated, and the solution is dis-

tributed entirely among the ampules. All the constric-

tions are rinsed simultaneously (in this manner, the con-

centration is not greatly disturbed), and the ampules are

taken.

The concentration of the reagent may be roughly

established quite easily by use of the sacrificial ampule.

The ampule is broken open, quenched into a large excess

of water, and titrated with HCl to a phenolphthalein end-

point.

The Gilman double titration is an alternative.20 In this

case, two sacrificial ampules are needed; the first is

treated as mentioned previously, and the second is

treated as follows: the ampule is quenched into a solu-

Figure 37. Transfer of Li metal to the apparatus.


tion that contains a reactive electrophile such as benzyl

bromide; the product of this reaction is then titrated with

HCl to a phenolphthalein end point. The concentration

of organolithium is manifested in the difference between

the two titration results. In practice, this titration is

rarely done in our laboratory.

Instead, it is assumed that the results of the simple

titration are near the actual value. An ampule of sec-BuLi is then diluted to a useful concentration, and a title

polymerization of styrene is accomplished under strict

high-vacuum conditions. The concentration of the initia-

tor is then accurately established based upon the results

of this polymerization:

Molarity ¼ ðGrams of monomerused=MW of PSÞVolume of initiator used

where MW is the molecular weight. sec-BuLi is quite

stable, sealed in glass under vacuum at cold tempera-

tures. It may often be kept for periods of up to several

years at �20 8C. Once the reagent begins to deteriorate

(as evidenced by cloudiness or precipitate in the

ampules), the decomposition seems to progress further

much more quickly.

For purposes of routine dilution and transfer to subse-

quent apparatuses, purging the new initiator apparatus

may generally be omitted, provided that the glass is

clean and the apparatus is thoroughly dried on the vac-

uum line. However, when very dilute solutions of initia-

tor must be used, or when it is best to exclude traces of

alkoxide (e.g., titration results of macroanions upon

chlorosilanes are very sensitive to aggregation phenom-

ena), then it is best to insist that the reagent be kept as

clean as possible.

(1,3-Phenylene)bis(3-methyl-1-phenylpentylidene)Dilithium Initiator (DLI) Synthesis

DLI,21 a difunctional hydrocarbon-soluble organo-

lithium initiator, is synthesized through a twofold adduc-

tion of sec-BuLi to a difunctional monomer that cannot

itself polymerize. The chemical reaction is given here:

This reaction is accomplished inside another variation

of an all-glass synthetic apparatus,19 which is shown

in Figure 40. The preparation of the synthesis requires

purification and ampulization of 1,3-bis(1-phenylethe-

nyl)benzene (PEB),22 preparation and ampulization of

sec-BuLi, purification of hexane, and purification of

benzene. PEB is purified over n-BuLi and collected

with a coerced distillation at 140 8C. PEB is used as

the limiting reagent, typically on a scale of 0.5–2 g,

depending on need. sec-BuLi is ampulized in a quan-

tity of at least 2.1 equiv of PEB. Ampules of PEB and

sec-BuLi are assembled to the vacuum synthetic appa-

ratus. Hexane and benzene are left on the vacuum line

in purified reservoirs (over BuLi and PSLi, respectively).

The synthesis of DLI is now fully described in a step-

by-step account and illustrated by Figures 40–44.

I. The apparatus is assembled, as shown in Figure 40,

docked to the vacuum line, evacuated, verified for integ-

rity by use of the Tesla coil, and flame-dried. The appa-

ratus is left to degas until a high vacuum is achieved.

II. BuLi is injected into the purge flask, the side arm is

rinsed and sealed, and the apparatus is degassed.

Figure 38. Reactor flask in which the chemicalreaction between Li metal and sec-BuCl occurs.

HIGHLIGHT 6203

III. Hexane is in-distilled to the apparatus, and the

apparatus is again degassed.

IV. The apparatus is sealed and detached from the vac-

uum line.

V. The contents are thawed. The solution of BuLi is

used to wash the entire inner surface of the apparatus

and is then collected back to the purge recovery flask.

VI. The apparatus is carefully rinsed by being allowed

to reflux from the purge recovery flask for at least 2 h.

VII. Hexane is distilled to the reactor flask. It is not

necessary to collect a large amount because it is desired

to precipitate the product from this solution. (Keep in

mind that the reagents are already ampulized in hexane

as well.) For example, even at a �2-g scale of PEB, a

reaction volume of �50 mL hexanes is plenty. A small

quantity is easily collected to the downward appendages

from the reactor. The purge recovery section is detached

from the apparatus.

VIII. The apparatus is inverted; hexanes are collected

to the reactor flask (see Fig. 41). The reactor is set to stir

at room temperature.

IX. The seals to the ampules of PEB and sec-BuLi areruptured, and their contents are rinsed into the reactor

flask. The ampules may be detached.

X. The reactor is shielded from the light by being

wrapped loosely in foil. The reaction is left to progress

for 3 days. Both PEB and sec-BuLi are soluble; the DLI

adduct is insoluble with time and stable at room temper-

ature.

XI. The apparatus is inverted (see Fig. 42).

XII. The hexanes are collected to the bottom recovery

flask. Excess sec-BuLi (or any monoadduct byproduct)

is soluble and will be removed from DLI in this manner.

A sparing solubility of DLI will give the hexane a deep

red color, but this minimal loss of DLI is unimportant.

The recovery flask is detached from the apparatus.

XIII. The apparatus is reattached to the vacuum line by

means of the break-seal appendage (see Fig. 43). After a

high vacuum is obtained, the seal is ruptured.

XIV. Benzene is distilled into the reactor, and the

apparatus is detached from the vacuum line.

XV. DLI is dissolved in the benzene (see Fig. 44 to

view the complete remaining apparatus at this point).

The solution is collected across the filter and to the final

apparatus. The apparatus is rinsed well with the benzene

with a liquid-nitrogen-dipped towel strip. The final appa-

ratus is detached and reserved.

It is possible to store this solution in the freezer; how-

ever, because benzene freezes at 5 8C, be aware that

there is a risk of rupturing a break-seal. We have had

success at storing the reagent at room temperature for

many months. A polymerization must be accomplished

to establish the concentration of DLI. An additive is

advised to be used as a coinitiator with the use of this

reagent to break up the aggregations, promote the solu-

bility, and encourage a faster initiation event. We gener-

ally have good success with the use of lithium sec-but-oxide (sec-BuOLi).

sec-BuOLi Synthesis

sec-BuOLi, used as an effective coinitiator, is synthe-

sized from the alcohol by its reaction with Li metal

according to this chemical reaction:

sec-BuOH þ Li�!sec-BuOLiþ 1=2H2

The preparation of the synthesis requires ampulization

of sec-BuOH and purification of benzene. sec-BuOH is

dried over salt (e.g., MgSO4) on the vacuum line with

stirring overnight, degassed, and ampulized; subse-

quently, this ampule is attached to the synthetic appara-

tus. Benzene is chosen as the solvent because the prod-

Figure 39. Filtration of the product sec-BuLi solu-tion.


uct is not appreciably soluble in hexane; it may be left

on the vacuum line in a purified reservoir.

This synthesis is very similar to that of sec-BuLi; theapparatus needed is thus similar, except for the geomet-

ric provision that sec-BuOH must be poured into the

reactor and not distilled. A portion of the vacuum syn-

thetic apparatus required, showing mainly the geometric

distinction from the previous ones, is depicted in

Figure 45. The essential differences of this synthesis in

contrast to that of sec-BuLi are as follows:

� Benzene is used as the solvent instead of hex-

ane, so that the product remains soluble.

� sec-BuOH is allowed to enter the reactor by

gravity.

� The reaction is exothermic, so the addition is

made slowly with the reactor chilled in an ice

bath, but the product is stable; hence the reac-

tor may be allowed to warm to room tempera-

ture or even higher.

� A blue color of products is visible.� The reaction is allowed to progress for �2

days.� Because H2 gas is evolved, the vacuum decreases;

it is not mandatory to remove the gas because itwill not interfere with an anionic polymerization,but if the reaction were to be carried out on alarge scale, it would be perhaps wise to make aprovision for this removal by the addition of anextra break-seal to the apparatus.

Figure 40. Vacuum synthetic apparatus for the synthesis of DLI.

HIGHLIGHT 6205

POLYMERIZATION PROCEDURES INNONPOLAR SOLVENTS

Simple Technique1,2

The kinetics of polymerization in hydrocarbon media

are very slow, and this means that the order of incor-

poration of reagents into the solvent is not necessarily

crucial. A simple polymerization apparatus is shown in

Figure 46. A simple stepwise procedure is given next.

I. The apparatus is assembled, docked to the vacuum

line, evacuated, verified for integrity by use of the Tesla

coil, and flame-dried. The apparatus is degassed until a

high vacuum is achieved.

II. The solvent (e.g., benzene or cyclohexane) is in-dis-

tilled through the vacuum manifold from a purified res-

ervoir. The apparatus is frozen with liquid nitrogen and

degassed. The apparatus is sealed and detached from the

vacuum line at the constriction.

III. The solvent is thawed and allowed to warm to

room temperature. The seals to the reagents are ruptured.

The monomer (and additive) is added first and is fol-

lowed by the initiator. We accomplish the mixing of the

contents by simply tumbling the apparatus, rinsing the

ampules well, and collecting all contents back to the

main flask. Stirring is generally unnecessary.

IV. Afterward, the active polymer is deactivated by

rupturing the seal to the methanol.

When breaking seals, be aware of vapor pressures on

both sides. A highly volatile material (e.g., isoprene or

even diluted butadiene) should be chilled before the seal

is broken to avoid blowing the breaker too forcefully

and risking shattering it. It is also wise to avoid letting

Figure 41. Reactor flask in which the chemical reaction between PEB and sec-BuLioccurs.

Figure 42. Removal of hexane and excess reagentsfrom the product DLI.


breakers fall on the wrong end because they are weaker

from that side; again, the risk is shattering the breaker.

Sometimes even the glass walls of the reactor can be

shattered. The mixing of monomers with solvent is usu-

ally exothermic, so mix these reagents carefully to avoid

sudden fluctuations in vapor pressure.

The polymerization is left to proceed until all mono-

mer is consumed (�6–8 half-lives; this can be 1 or more

days, depending on the concentration and targeted MW).

Linear block copolymers are obtained by the sequen-

tial addition of monomers: each monomer is polymer-

ized before the addition of the next. The purity of the

second (or later) monomer must be very high because

any impurity will result in the premature termination of

active polymer chains and, hence, a homopolymer con-

taminant in the final polymer product.

Purge Technique2

Generally purging is required when the targeted MW is

high (>100 kg/mol) because there will be fewer moles

of initiator used and, hence, a lower tolerance for traces

of impurities. It is also necessary to employ this techni-

que in the provision of lower MW materials if precision

is required in the designed MW of the product.

The drawing in Figure 47 illustrates how a simple

polymerization may be easily modified to permit the

purging of the reactor. For example, by using such an

apparatus in the 1970s, Fetters23 was able to produce

polystyrene samples with controlled MWs in the range

of millions. Purging is accomplished by using the proce-

dure given here.







III. The solvent is in-distilled through the vacuum

manifold from a purified reservoir. The solvent is frozen

with liquid nitrogen, and the apparatus is degassed. The

apparatus is sealed and detached from the vacuum line

at the constriction.

IV. The contents are thawed. The solution of BuLi is

used to wash the entire inner glass surface, by careful

tumbling of the apparatus, and is then collected back to

the purge recovery flask.

V. The apparatus is rinsed. By gently warming the

solution in the purging recovery flask, the solvent is

condensed throughout the reactor. This solvent collects

in the reactor flask and is poured back into the purge

Figure 43. In-distillation of benzene to the reactorflask.

Figure 44. Product DLI solution collected to finalsplit-down apparatus.

HIGHLIGHT 6207

recovery flask by careful tilting of the apparatus. Repeat-

ing this periodically for a period of �2 h allows the col-

lection of all BuLi, along with its reaction products with

the impurities on the surface of the glass (which are also

nonvolatile), back to the recovery flask.

VI. The solvent is gently distilled from the purge

recovery flask (20 8C) to the polymerization reactor flask

(0 8C). Finally, the purge flask is detached from the

apparatus by the sealing of the constriction.

VII. At this point, the polymerization is set to com-

mence upon the rupture of the break-seals. The proce-

dure to be followed from this point onward is the same

as that described for the simple technique.

During the rinsing of the polymerization reactor

and the final distillation of the solvent to the reactor, it

is very important to prevent the BuLi solution bump-

ing from the purge flask into the polymerization reac-

tor. Bumping is avoided more easily with a lower tem-

perature differential as the motive of distillation.

Avoiding the use of overly filled flasks is also helpful

(i.e., it is best to plan that the reactor be not more than

half full).

Delayed Ampulization

A monomer may, in some cases, be ampulized immedi-

ately before its use. There are two frequent situations

that call for this technique: (1) the monomer is danger-

ously volatile at room temperature, or (2) the monomer

is unstable upon purification. Figure 48 illustrates how

an empty freeze ampule may be fitted directly to a poly-

merization reactor. The overall procedure is thus a com-

bination of the earlier given accounts of polymerization

and freeze ampulization, appropriately timed.

I. The polymerization is prepared up to the point of the

need of the monomer, at which point the apparatus exists

as shown in Figure 48. The apparatus is then redocked to

the vacuum, and the empty ampule is used to collect the

needed monomer by using the appropriate ampulization

technique for the selected monomer.

II. The monomer is taken by sealing the constriction,

whereupon it is immediately incorporated into the poly-

merization.

The delayed monomer may be collected to a reactor

waiting for polymerization to commence, or it may be

added to a polymerization already in progress (e.g.,

preparation of a diblock).

Figure 45. Vacuum synthetic apparatus for the synthesis of sec-BuOLi: a partialdepiction.


This technique is a useful way to avoid requiring the

dilution of overly volatile monomers such as butadiene.

It is also a good way to retain a high purity of unstable

monomers because they are incorporated at once into

the reactor, diluted, and placed into the scene of their

desirable consumption.

Canadian Technique in Detail3,24,25

An alternative geometry of an all-glass apparatus, which

permits purging, is shown in Figure 49. This apparatus

was developed and highly refined by the Canadian

school of anionic polymerization, during the 1960s and

1970s, an elegant culmination of contributions from

Worsfold, Bywater, and Roovers, among others. The

technique remains timeless and lends itself easily toward

new chemistries as they are explored. A detailed step-

by-step account of manipulations is given here and is

supported pictorially by Figures 49–54.

I. The apparatus in Figure 49 is assembled, docked to

the vacuum line, evacuated, verified for integrity by use

of the Tesla coil, and flame-dried. The apparatus is

degassed until a high vacuum is achieved.



III. The solvent is in-distilled through the vacuum

manifold from a purified reservoir. The solvent is frozen

with liquid nitrogen, and the apparatus is degassed. The



IV. The contents are thawed. The solution of BuLi is

used to wash the entire inner glass surface by careful

tumbling of the apparatus and is then collected back to

the purge recovery flask.

V. The apparatus is rinsed. By the apparatus being

stood upright in a warm water bath, the solvent is

allowed to reflux from the purge recovery flask to the

reactor (see Fig. 50).

Figure 46. Simple polymerization apparatus.

HIGHLIGHT 6209

VI. The rinsing is continued for 2 h. The solvent may

be collected to the remote appendages (by means of a

towel strip dipped in liquid nitrogen, see Fig. 51). The

apparatus may need to be periodically tilted, and the

recovery flask briefly chilled in a 0 8C bath, to facilitate

the intermittent collection of all solvent back to the

recovery flask from remote pooling locations within the

reactor. (By careful construction, gravity will accom-

plish most of the solvent return. However, the down-

wardly pointing attachments must be raised above the

horizontal to drain.)

VII. The solvent is collected to the reactor in a gentle

distillation procedure, as shown in Figure 52.

VIII. The purge section is detached from the polymer-

ization apparatus. The remaining polymerization appara-

tus is shown in Figure 53.

IX. The polymerization is commenced.

The basic Canadian apparatus is easily adapted. For

example, with an apparatus such as the one shown in

Figure 54, a polymerization from DLI is accom-

plished.26 The monomer, the initiator, and the coinitiator

are all attached to the same arm. After the polymeriza-

tion, an estimated amount of solution is collected into

the sampling arm, where it may be detached and then

quenched with methanol. Finally, a carefully calculated

quantity is ampulized in the collection flask.

Note that the collection flask is fitted with a con-

stricted break-seal exit; the solution may be mixed with

another reactor, and the entire mixed contents may be

Figure 47. Polymerization apparatus adapted to a purge technique.

Figure 48. Delayed ampulization technique.


back-collected to the same flask and reampulized to

await final linking chemistry. THF may be finally added

and the linking progress may be monitored by use of the

small sampling ampules.

POLYMERIZATION PROCEDURES IN THF

Simple Technique

The anionic polymerization of vinylic monomers inTHF is a much more sensitive procedure than their

polymerization in hydrocarbon media. THF is anactive solvent, and the kinetics of the polymerization

are much faster. The reactor must be briskly and con-

tinuously stirred. Polymerizations are generally ac-complished within minutes instead of hours. The

advantage of using THF is that it is a more versatile

solvent. Hence, a larger variety of monomers may bepolymerized in this solvent. Keep in mind that in the

polymerization of dienes, the microstructure obtained

is very sensitive to the media. (The so often desirable,rubbery, cis-1,4 microstructure is obtained only

through polymerization in hydrocarbon media with Licounterion.)

A basic all-glass apparatus suitable for polymeriza-

tions in THF is shown in Figure 55. A modest step-by-

step account of its use follows presently.





Figure 49. Canadian polymerization apparatus.

HIGHLIGHT 6211

II. The apparatus is closed from the vacuum. The seal

to n-BuLi is ruptured, and the initiator is rinsed into the

reactor with the hexanes.

III. The reactor is set to bathe at �78 8C in a dry ice/

isopropyl alcohol bath. THF is distilled into the reactor

from a purified reservoir on the vacuum manifold. The



IV. Monomers are sequentially incorporated into the

reactor; each is allowed a brief period to polymerize

before the seal to the next one is ruptured.

V. The polymerization is quenched by rupturing of the

seal to the methanol. The apparatus is allowed to warm

to room temperature.

During the polymerization, the external alcohol bath

should be set to bathe the apparatus at a level beneath

the level of the solvent inside the reactor. Otherwise, as

monomers are incorporated, it is easy for them to accu-

mulate and polymerize on the glass above the level of

the solution, and an inhomogeneous system results.

The initiator used is n-BuLi rather than sec-BuLi.sec-BuLi may react with THF somewhat more rapidly

than n-BuLi, even at �78 8C. The active polymer chains

may also be terminated if the reactor is allowed to warm

during the polymerization. It is consequently difficult to

take preliminary aliquots of the polymerization between

additions of successive monomers.

Monomers may not be poured into the reactor

without being diluted first in THF. If they are diluted

and poured, they must be well chilled before the rup-

turing of break-seals. Alternatively, the monomers

may be distilled to control the polymerization better.

Distillation is recommended for the addition of all

monomers after the first one because the reactor is

Figure 50. Rinsing of the apparatus.

Figure 51. Remote rinsing of the apparatus.


not purged: distillation is the cleanest method of

monomer transport. When using the distillation techni-que, it is wise to begin the distillation with the mono-

mer cold and then allow it to gently warm, after the

break-seal is ruptured, to avoid bumping the monomerinto the reactor.

In the synthesis of block copolymers, the reactivity ofeach monomer must be considered in determining thepolymerization sequence. That is, in anionic polymeriza-tion, the resulting anionic chain end of each sequential

polymerization must be reactive enough to quickly ini-

tiate the polymerization of the next monomer. Consider

the following reactivity scale:27

Styrenes � Dienes > Vinylpyridines >

ðMethÞacrylates > Siloxanes � Oxiranes

In other words, the anionic polymerization of each mono-

mer in the scale leads to a macroanion reactive enough to

initiate a polymerization of any monomer to its right.

Figure 52. Distillation of the solvent from the purge attachment to the polymeriza-tion reactor.

Figure 53. Canadian polymerization apparatus: final apparatus.

HIGHLIGHT 6213

Polymerization of (Meth)acrylates

It will be understood by now that the subtle variance

among more elaborate glass apparatuses becomes as rich

as the synthesist’s skill and imagination permit. The

apparatus shown in Figure 56 is an example of such, as

developed by Cook.28 The polymerization procedure is

very similar to that described for the previous simpler

apparatus; therefore, a new step-by-step account is not

provided here.

An effective organolithium for the initiation of

(meth)acrylates is diphenylalkyllithium. This initiator is

generated in situ through the interaction of a stoichio-

metric quantity of n-BuLi with excess DPE. Of course,

there is no inherent drawback in the earlier preparation

of this organolithium. However, this delayed approach

offers greater flexibility in the synthesis of diblocks.

More reactive monomers (e.g., styrenic compounds)

may be polymerized first from n-BuLi; the resultant

Figure 54. Canadian polymerization apparatus: complex apparatus example.


macroanions are then end-capped with DPE before the

cross-initiation of (meth)acrylate.

The glass finger entry to the reactor helps to deliver

the monomer directly into the vortex of the stirring THF

solution. The glass path may be gently warmed with the

hand torch before such distillations to dissuade mono-

mers from stopping there and clogging the path. After

using the torch in warming the glass, allow the reactor to

become tepid before rupturing the seal to the monomer

ampule.

Additives may generally be omitted in the polymer-

ization of methyl methacrylate. More reactive methacry-

lates and acrylates are often better controlled during pol-

ymerization through the addition of LiCl or LiClO4 to

dissuade side reactions. Such compounds are completely

nonvolatile and should be attached as closely to the reac-

tor as possible.

Purge Technique

A reactor to be used for polymerization in THF is less

frequently purged than one used for polymerizations in

hydrocarbon media because of increasing difficulty.

However, this procedure may be accomplished. The

purging agent used is diphenylhexyllithium because

this organolithium is less reactive toward THF solvent,

and the procedure is accomplished at room tempe-

rature (without greatly warming the purge flask to

effect distilling or refluxing of THF). We can very

easily prepare this reagent as a stock solution by

adding DPE to a bottle of n-BuLi and keeping it for

multiple procedures.

The glass apparatus shown in Figure 57 is useful

for this experiment, illustrating a geometry that we

have learned from Pitsikalis.3 After the injection of the

purging agent, THF is in-distilled, and the apparatus is

sealed. The apparatus is washed and rinsed by gentle

distillation of the THF from the purge flask to the rest

of the apparatus and its recollection back to the purge

recovery flask several times. Because diphenylhexyl-

lithium is attended by a deep red hue, it is easy to dis-

cern when the apparatus has been sufficiently rinsed.

THF is carefully distilled to the polymerization reactor

and chilled, and the purge section is detached.

Because the purging procedure requires a frequent

tumbling of the apparatus, it is rather difficult to keep

unstable monomers continuously cold. A delayed ampu-

lization technique may therefore be necessary. The appa-

ratus in Figure 57 shows this specific provision for one

of its ampules.

LINKING MANIPULATIONS USINGCHLOROSILANES: HELLENICTECHNIQUE IN DETAIL3

The group of Hadjichristidis, Iatrou, Pispas, and Pitsika-

lis has developed and refined careful linking techniques

Figure 55. Simple polymerization apparatus for use with the solvent THF.

HIGHLIGHT 6215

and exploited a modular linking chemical strategy, offer-

ing a strong synthetic methodology toward a wide vari-

ety of well-defined miktoarm (mixed arm; i.e., hetero-

arm) materials, as well as more complex graft materials

such as ps and multigrafts.26,29–33 This linking strategy

is likely to remain another timeless example of a synthe-

sist’s art over both glass and chemistry.

The basic Hellenic linking apparatus is shown in

Figure 58. The reactor is designed so that each manipu-

lation is conducted through its own break-seal entry or

exit to the reactor. In some cases, a clean delivery of pol-

ymer solution into the reactor is enhanced by the use of

an inwardly protruding fingertip extension of the entry

directly into the main reactor flask (illustrated more

clearly in the following sketches). Intermediate sampling

is permitted by means of small ampules attached to the

reactor; thus, linking progress may be monitored by size

exclusion chromatography (SEC).

In the scene of Figure 58, a typical reactor is shown

at the beginning of its use. The reactor is purged with a

benzene solution of BuLi and rinsed, absolutely, for at

least 4 h or better for 2 days while other work is done.

Finally, a small amount of benzene is collected to the

linking reactor (in the appendages), and the purge recov-

ery flask is detached.

The linking reactor is at this point ready to be sealed

toward the ampulized products of controlled anionic

polymerizations through further glassblowing. Various

manipulations each require a specific further assembly.

These all-glass assemblies are further described in the

following subsections and illustrated through the use of

Figures 59–62 and 64.

Assembly of the Reactor to Flasks of CollectedActive Polymer29

After the linking apparatus is prepared, the chlorosilane

compound is introduced into the reactor. The empty

ampule may be detached for a less clumsy apparatus.

Each active polymer ampule is attached to the linking

reactor through the assembly of an all-glass bridge (see

Fig. 59 to visualize this construction). A double breaker

(a breaker with a heavy collection of glass at both ends)

is used. This assembly is carefully docked to the vacuum

Figure 56. Polymerization apparatus useful for the polymerization of (meth)acry-lates in THF.


port (always use two persons for this step) and gently

supported under each flask. The bridge is vacuumed for

at least 1 h or until a high vacuum is attained.

The assembly is taken by the sealing of the constric-

tion. It is urged that this be done only with two persons:

two hands are not enough. The assembly is then trans-

ported to a safe location. It is urged again that the appa-

ratus always be well supported under both flasks because

their weight, especially if full, may introduce a lot of

stress on the glass bridge and the break-seals between

the two flasks.

The assembly is thus prepared for commencement of

the linking event. The manner in which this manipula-

tion is conducted is crucial to the success of the proce-

dure and is described presently.

End-Capping the Active Polymer withExcess Chlorosilane34,35

For the end-capping step to be successful, two things are

important. First, the amount of silane used should be a

great excess over the amount of active polymer chains;

if it is possible, use a 100-fold excess. Second, the solu-

tion of active polymer must be added to the silane in one

motion, without the silane being permitted to migrate

(simple chlorosilanes are more volatile than benzene)

into the flask of active polymer.

The second criterion is actually not difficult to

achieve. Keeping the linking reactor cooler than the

flask of active polymer, along with gravity, pulls the sol-

ution rather easily into the linking reactor. The linking

reactor may be set to stir briskly in a pan of water; ice is

added to the pan; and 30 s later (because benzene freezes

at 5 8C, the reactor cannot be left at 0 8C for a long

time), the seals are ruptured, and the assembly is tilted

steeply, with a hand kept on the flask of active polymer

for both warmth and support. Additionally, a towel

soaked in warm water may be cloaked briefly around the

flask of active polymer for a few seconds to raise its

vapor pressure.

The addition event is pictured in Figure 60. The solu-

tion is thus added in one continuous increment to the

linking reactor with brisk stirring throughout. After the

addition has taken place, the assembly may be allowed

to lie flat at room temperature. The incorporation of the

first equivalent of active polymer chain into a chlorosi-

lane is generally accomplished within several minutes,

although we usually wait hours. As colored anions are

adducted into Si, a visual indication is that their color

completely dissipates. If the solution is concentrated, a

light precipitation of LiCl may be noticed; this is incon-

sequential to the linking progress and indeed is evidence

of the success.

Figure 57. Polymerization apparatus useful for THF polymerizations requiring apurge technique.

HIGHLIGHT 6217

Removing Excess Chlorosilane34,35

Excess volatile chlorosilane is removed after the end-

capping procedure by means of the high-vacuum line.

The reactor is assembled to the vacuum manifold

through one of the break-seal entries. It is possible to

use complementary ground glass joints and high-vacuum

grease; however, because of the long experimental dura-

tion and sensitivity of the procedure, this is discouraged.

The better technique is to assemble the reactor

directly to the vacuum manifold through an all-glass

path (see Fig. 61 to visualize this assembly). Depending

on the glassblowing style, two persons may be required

for the assembly. The most important result is that there

must be no stress on the glass bridge. Therefore, after

roughly attaching the apparatus, clamp the linking reac-

tor securely; if the reactor is large, two perpendicularly

oriented clamps are better. The final glassblowing is then

Figure 58. Hellenic linking apparatus.

Figure 59. All-glass assembly of the linking reactor to a flask of active polymer.


completed and the connection is annealed for several

minutes with the hand torch, with a soft blue-yellow

flame. Neither the clamps nor the apparatus is adjusted

after this point.

Elsewhere docked to the vacuum manifold are a res-

ervoir of purified benzene and a large waste collection

flask, which are both well degassed. The stopcock to the

linking reactor is opened, and the glass path is pumped

until a high vacuum is achieved.

The seal to the reactor is broken, and the contents are

out-distilled to the waste collection flask until the solu-

tion becomes too viscous to stir. Freshly purified ben-

zene is in-distilled to the reactor to make a �10 w/v %

solution, and the contents are stirred to mix them well.

The contents are again out-distilled. This procedure is

repeated for a total of three out-distillations. After the

third out-distillation, all of the solvent is carefully

stripped from the polymer; the stopcock is carefully

adjusted to avoid letting the polymer climb out the reactor.

During the in-distillations, it is extremely dangerous

to freeze the linking reactor with either dry ice or liquid

nitrogen. Often the thick polymer syrup is strongly adhered

to the glass, or the system freezes in an inhomogeneous

manner. (Two different layers of the substance freeze: one

is the concentrated polymer solution, and the other is the

incoming solvent.) The result is that a lot of stress is placed

on the flask; often mechanical failure cannot be prevented,

and the glass cracks. It is strongly recommended to simply

use ice water to chill the reactor, gently, while both the res-

ervoir and the reactor are stirred.

After the majority of solvent has been stripped from

the polymer and it appears to become drier, the reactor

may be opened directly to the main vacuum manifold.

The main liquid-nitrogen trap must be cleaned after the

first day. It is important to fill the main liquid-nitrogen

Figure 61. All-glass assembly of the reactor directly to the high-vacuum line.

Figure 60. Addition of a solution to the linkingreactor.

HIGHLIGHT 6219

trap vigilantly (twice per day). The reactor is pumped

for 1 week under a high vacuum. The reactor may be left

at room temperature. Optionally, the reactor may be gen-

tly warmed to 35 8C for a slightly faster evacuation.

After 1 week, purified benzene is once more in-dis-

tilled to the linking reactor from the purified reservoir.

The linking reactor is detached from the vacuum line,

with two persons, by sealing the constriction. The poly-

mer is left to dissolve overnight.

An aliquot of the solution should be taken and com-

pared with the sample of the quenched polymer before

the end capping. SEC eluograms, before and after the

end-capping procedure, should coincide and lack evi-

dence of dimerization of the macroanions.

Titration of the Active Polymer intoStoichiometric Chlorosilane29,30

High-vacuum titration is an elegant procedure in which

active polymer is added from a collection flask to the

linking reactor incrementally. After each addition is

made, a small quantity (several drops are sufficient) is

removed from the linking reactor to monitor the linking

progress with SEC. The discriminatory powers of chlor-

osilane electrophilic centers toward incoming macromo-

lecular nucleophiles, based on their steric demands, is

exploited fully.

Because it is much more difficult to add a third arm

of polystyrene to Si than it is to add a second one, it is

Figure 62. Titration of a solution into the linking reactor.

Figure 63. SEC eluogram composition (see the text for an explanation).


possible to titrate the second equivalent of PSLi cleanly.

Similarly, PILi may be titrated as a third equivalent. It is

important that the aggregation behavior of the macroor-

ganolithiums be controlled for a highly successful result.

Alkoxides, which do not affect the course of a polymer-

ization, may influence the linking behavior. THF is a

powerful additive and generally results in a marked

enhancement of linking behavior and is, in most cases,

avoided in titration procedures.

Figure 62 depicts a titration in progress, for which a

Hellenic linking reactor has been assembled to a flask of

PSLi. By the careful raising and lowering of the flask of

active polymer, dropwise additions of the solution to the

linking reactor are controlled.

Because PSLi is evidenced by a vivid orange-red hue,

the progress of linking may be visually monitored in a

qualitative way. SEC is the more important inspection,

however, and eyes should never be relied on alone.

Moreover, the relative height of each of the peaks in the

SEC eluogram will give a quantitative impression of the

progress of the titration, from which the size of the next

future increment may be decided.

The SEC composition shown in Figure 63 is exem-

plary: a titration of PSLi upon SiCl4 is illustrated in a

waterfall plot. Here SEC eluograms of successive ali-

quots taken during the titration procedure are normalized

with respect to the maximum peak height and are

stacked toward the viewer sequentially. The first aliquot

(backmost eluogram) indicates a mixture of 25%

(PS)2SiCl2 dimer and 75% PSSiCl3 unimer by mass. At

the point of the second aliquot, the amount of the dimer

has increased to 60%. Repeated small additions of PSLi

to the reactor are attended by a steady decrease in the

unimer content to less than 5%, whereas the high-MW

shoulders of the later eluograms show no evidence of

the formation of (PS)3SiCl trimer.

The titration is stopped when it is judged that there is

no further progress in the shift of the SEC profile. Usu-

ally there remains a small quantity of unlinked material

in the reactor. Often there will be a visual cue that the

solution in the linking reactor remains more colored.

Occasionally there will be evidence of overtitration (a

small and unwanted high-MW shoulder grows), at which

point the titration should generally be stopped.

Final Linking Manipulations

We make final linking manipulations by collecting solu-

tions of macromolecular electrophiles and nucleophiles

together in a certain stoichiometry, sealing them in a

convenient storage flask, and waiting for the linking to

occur (see Fig. 64 to visualize a final assembly of macro-

molecular reagents).

Notice that the final collection flask is equipped with

a constricted break-seal exit. After the solutions are

mixed, they are collected back into this new flask and

reampulized.

The final macromolecular organolithium is often end-

capped with several units of butadiene to relieve steric

barriers. It is generally used in excess over the remaining

Si��Cl bonds (�1.2 equiv). The final linking reaction is

usually permitted several weeks. A small amount of

THF may be added (�0.5 v/v %); this breaks up the

aggregations and expedites linking events. Often 1 week

in the presence of THF is sufficient for all linking to

progress.

The final linking is monitored by the removal of

small aliquots and their analysis with SEC. When no fur-

Figure 64. Final all-glass encapsulation to permit long-term linking completion.

HIGHLIGHT 6221

ther shift toward a higher MW is discerned according to

the SEC profile, the linking is judged to be complete.

CONCLUSIONS

In this compilation, we have attempted to collect and

provide thorough, easy-to-follow, step-by-step instruc-

tions for performing the key manipulations that are

required to accomplish syntheses of complex macromo-

lecules through controlled anionic polymerization under

high-vacuum conditions in all-glass reactors. We have

placed special emphasis on technique, instilling an

appreciation of the requirements of a vacuum system

and the behavior of compounds within it, and also on

safety because of the hazardous nature of certain manip-

ulations. We sincerely hope that this work will be useful

to workers in this field, especially to novices as they

seek to master these highly specialized techniques.

The authors acknowledge current sponsorship by the

Division of Materials Sciences and Engineering, Office of

Basic Energy Sciences, U.S. Department of Energy, under

contract DE-AC05-00OR22725 with Oak Ridge National

Laboratory, which is managed and operated by UT-Bat-

telle, LLC. D. Uhrig is supported by an appointment to

the Oak Ridge National Laboratory Postdoctoral Research

Associate Program, which is administrated jointly by the

Oak Ridge Institute for Science and Education and Oak

Ridge National Laboratory.

The authors are grateful to the referees for their many

excellent criticisms and suggestions for improving this article.

The authors are also grateful to the editors for bringing the

work to fruition. J. W. Mays thanks Lew Fetters, Cheong

Kow, and Barry Hostetter for introducing him to the joys of

high-vacuum anionic polymerization. D. Uhrig thanks Mari-

nos Pitsikalis, Yiannis Poulos, and Kunlun Hong: Real living

polymers.

REFERENCES AND NOTES

1. Fetters, L. J. J Res Natl Bur Stand Part A: PhysChem 1966, 70, 421.

2. Morton, M.; Fetters, L. J. Rubber Chem Technol

1975, 48, 359.3. Hadjichristidis, N.; Iatrou, H.; Pispas, S.; Pitsikalis,

M. J Polym Sci Part A: Polym Chem 2000, 38, 3211.4. Morton, M. Anionic Polymerization: Principles and

Practice; Academic: New York, 1983.5. Hsieh, H.; Quirk, R. Anionic Polymerization: Princi-

ples and Practice; Marcel Dekker: New York, 1996.

6. Hong, K.; Uhrig, D.; Mays, J. W. Curr Opin SolidState Mater Sci 2000, 4, 531.

7. Hadjichristidis, N.; Pispas, S.; Floudas, G. BlockCopolymers: Synthetic Strategies, Physical Properties,and Applications; Wiley: New York, 2003.

8. Alberty, K. A.; Tillman, E.; Carlotti, S.; King, K.;Bradforth, S. E.; Hogen-Esch, T. E.; Parker, D.;Feast, W. J. Macromolecules 2002, 35, 3856.

9. Chen, R.; Nossarev, G. C.; Hogen-Esch, T. E. JPolym Sci Part A: Polym Chem 2004, 42, 5488.

10. Pitsikalis, M.; Siakali-Kioulafa, E.; Hadjichristidis, N.Macromolecules 2000, 33, 5460.

11. Pitsikalis, M.; Siakali-Kioulafa, E.; Hadjichristidis, N.J Polym Sci Part A: Polym Chem 2004, 42, 4177.

12. Vazaios, A.; Pitsikalis, M.; Hadjichristidis, N. JPolym Sci Part A: Polym Chem 2003, 41, 3094.

13. Fragouli, P. G.; Iatrou, H.; Hadjichristidis, N. JPolym Sci Part A: Polym Chem 2004, 42, 514.

14. Nasser-Eddine, M.; Reutenauer, S.; Delaite, C.;Hurtrez, G.; Dumas, P. J Polym Sci Part A: PolymChem 2004, 42, 1745.

15. Higashihara, T.; Hirao, A. J Polym Sci Part A:Polym Chem 2004, 42, 4535.

16. Quirk, R. P.; Guo, Y.; Wesdemiotis, C.; Arnould, M.A. J Polym Sci Part A: Polym Chem 2003, 41, 2435.

17. Quirk,R. P.;Gomochak,D. L.;Wesdemiotis, C.; Arnould,M.A. J PolymSci PartA: PolymChem2003, 41, 947.

18. Shriver, D. F.; Drezdzon, M. A. The Manipulationof Air-Sensitive Compounds, 2nd ed.; Wiley-Inter-science: New York, 1986.

19. Pispas, S.; Pitsikalis, M.; Hadjichristidis, N.; Dardani,P.; Morandi, F. Polymer 1995, 36, 3005.

20. Gilman, H.; Cartledge, F. K. J Organomet Chem1964, 2, 447.

21. Tung, L.; Lo, G. Macromolecules 1994, 27, 1680.22. Ignatz-Hoover, F. Ph.D. Thesis, University of Akron,

1989.

23. Fetters, L. J. Science 1972, 176, 1041.24. Roovers, J.; Toporowski, P. M. Macromolecules

1983, 16, 843.25. Worsfold, D. J.; Bywater, S. Can J Chem 1960, 38, 1891.26. Gido, S. P.; Lee, C.; Pochan, D. J.; Pispas, S.; Mays,

J.W.; Hadjichristidis, N.Macromolecules 1996, 29, 7022.27. Jerome, R.; Teyssie, P.; Vuillemin, B.; Zundel, T.;

Zune, C. J Polym Sci Part A: Polym Chem 1999, 37, 1.28. Cook, D. C. Ph.D. Thesis, University of Alabama at

Birmingham, 1998.29. Iatrou, H.; Hadjichristidis, N. Macromolecules 1992,

25, 4649.30. Iatrou, H.; Hadjichristidis, N. Macromolecules 1993,

36, 2479.31. Hadjichristidis, N. J Polym Sci Part A: Polym Chem

1999, 37, 857.32. Iatrou, H.; Mays, J. W.; Hadjichristidis, N. Macro-

molecules 1998, 31, 6697.33. Uhrig, D.; Mays, J. W. Macromolecules 2002, 35, 7182.34. Pennisi, R. W.; Fetters, L. J. Macromolecules 1988,

21, 1094.35. Mays, J. W. Polym Bull 1990, 23, 247.


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