How Can Multi-Detector SEC Inform our Knowledge …...Striegel, Yau, Kirkland, Bly, Modern...

How Can Multi-Detector SEC

Inform our Knowledge of

Mechanochemical Polymer

Degradation?

André M. Striegel

National Institute of Standards & Technology

Objectives

• Use size-exclusion chromatography with multi-angle static light scattering and viscometricdetection to study effects of polymer architecture on transient elongational flow degradation.

• Attempt to isolate effects of long-chain branching(LCB) and conformation on degradation.

• Use ultrasonication as representative transient elongational flow degradation technique.

• Combine multi-detector SEC and ultrasonicationto examine consequences for Mlim.

The Rayleigh-Plesset Equation

RR

RtPPpRRR g

24)(

1

2

30

2

2

2

dt

RdR

dt

dRR

bubbleradius of R

liquid ofdensity

liquid of tension surface

liquid ofviscosity kinematic

ressureexternal p dependenttimetP

essureambient prP

bubblere inside gas pressupg

)(

0

Adapted from K. S. Suslick, in Encyclopedia of Physical

Science and Technology, 3rd ed., R. A. Meyers, ed. (2001)

Ultrasonication

Temporal Evolution of Bubble Radius and Strain Rate

During Cavitational Bubble Collapse

Adapted from TQ Nguyen, H-H Kausch, Int. J. Polym. Anal. Charact., 4 (1998) 447

Interest in Ultrasonic Degradation

• Bubble collapse gives rise to large shear gradients responsible for ultrasound-induced bond scission.

• Collapse of cavitation bubble creates transient elongational flow.

• Two general types of flow fields:

– Shear

– Extensional

• Two types of extensional flow

– Steady state

– Transient elongational (a.k.a. fast transient)

• Note that shear field polymer degradation is extremely rare.

Interest in Ultrasonic Degradation

• Collapse of cavitation bubble creates transient elongational flow.

• In transient elongational flow, “dwell time” of fluid element very short compared to relaxation time of macromolecule.

• Results in non-random, near-midchain scission of linear polymers.

• Laboratory-created flow fields strictly analogous to those found in many real world scenarios.

Advantages of Ultrasonication

• Fluid mechanics and kinetics:

Comparable to other means of

generating transient elongational flows.a

• Relatively simple to isolate individual

experimental variables.

• Minimal sample consumption.

aTQ Nguyen, QZ Liang, H-H Kausch. Polymer, 38 (1997) 3783

TQ Nguyen, H-H Kausch. Adv. Poly. Sci., 100 (1992) 73

ULTRASONIC DEGRADATION

“Contrary to all chemical or thermal decomposition reactions, ultrasonic

depolymerization is a nonrandom process that produces fragments of definite molecular size.

Cavitation provides the most effective source of mechanical energy capable of causing the

specific degradation of macromolecules”

AM Basedow, KH Ebert, “Ultrasonic degradation of polymers in solution,”

Adv. Polym. Sci., 22 (1977) 83-148

Our Lab: The Last 15 Years

• AM Striegel, J. Biochem. Biophys. Methods 56 (2003) 117-139.

• AM Striegel, Biomacromolecules 8 (2007) 3944-3949.

• SG Ostlund, AM Striegel, Polym. Degrad. Stab. 93 (2008) 1510-1514.

• AM Striegel, J. Liq. Chromatogr. Rel. Technol. 31 (2008) 3105-3114.

• MJ Morris, AM Striegel, Polym. Degrad. Stab. 97 (2012) 2185-2194.

• AM Striegel, J. Chromatogr. A 1359 (2014) 147-155.

Influence of Long-Chain Branching

on

Transient Elongational Flow

Degradation

Ultrasonication of Branched Polymers

• Dextran (Lorimer et al. 1995, Côté & Willett 1999)

• Guar galactomannan (Tayal & Khan 2000)

• Xanthan (Sohn et al. 2001)

• Poly(vinyl acetate) (Madras et al. 2000, 2001…)

• Cellulose derivatives (Schittenhelm & Kulicke 2000)

• Starch derivatives (Schittenhelm & Kulicke 2000)

• Other long-chain branched glucans (Zhan et al. 2001)

POLYSTYRENE: Linear vs. Star

• 65,000 g/mol linear vs. 78,000 g/mol 8-arm star

(ea. arm: 9,800)


(ea. arm: 85,000)

vs. 202,000 g/mol 8-arm star

(ea. arm: 25,300)


(ea. arm: 45,500)

SG Ostlund, AM Striegel. Polym. Degrad. Stab., 93 (2008) 1510

AM Striegel. J. Biochem. Biophys. Methods, 56 (2003) 117

SEC/MALS/VISC/DRI

Solvent

Reservoir

(DMAc/0.5% LiCl)

Pump Injector Thermostatted

SEC columns

MALS

DRI VISC

Fluid connection

Electronic connection

47 kHz, 185 W

Comparison 1: PS-L 65 vs. PS-St8 9.8/78

• PS-L 65: Linear PS ~65,000 g/mol

• PS-St8 9.8/78: 8-arm star PS ~78,000 g/mol,

each arm ~9,800 g/mol

Results

• Sonicated for 4 hrs (240 min)

• PS-L 65:

– ~2% decrease in molar mass

– Increase in Mw/Mn from 1.001 to 1.004

– Decrease in []w from 0.22 to 0.21 dL/g

• PS-St8 9.8/78:

– No changes in MMD, polydispersities, etc.

• Conclusion:

“Limiting molar mass” 65,000 g/mol

Limiting Molar Mass, Mlim

• Molar mass beyond which macromolecules show no or negligible transient elongational flow-induced (ultrasonic) degradation

• Known to depend on chemical identity of polymer

• Also depends on physicochemical factors:

– Ultrasonic intensity

– Analyte concentration

– Solvent parameters: Ionic strength, temperature, viscosity, heat of vaporization, etc.

• Very limited information on architectural effects


Definition #1

A given polymer will not degrade in transient elongational

flow if M Mlim

or

Given two polymers of the same chemistry,

if M1 > Mlim and M2 Mlim,

Polymer 1 will degrade, but Polymer 2 will not.

For a given set of experimental conditions

Comparison 2: PS-L 257 vs. PS-St3 85/255

vs. PS-St8 25.3/202


• PS-St3 85/255: 3-arm star PS ~255,000

g/mol, each arm ~85,000 g/mol

• PS-St8 25.3/202: 8-arm star PS ~202,000


20 22 24 26 28 30 32 34

0

1

2

3

1.298.90.35

1.449.20.36

1.9410.90.45

2.3011.90.51

2.4412.50.54

2.5112.80.56

2.5713.20.57

Mw x 105

(g/mol)

R

(nm)

[]w

(dL/g)

1.298.90.35

1.449.20.36

1.9410.90.45

2.3011.90.51

2.4412.50.54

2.5112.80.56

2.5713.20.57

Mw x 105

(g/mol)

R

(nm)

[]w

(dL/g)

0 min

10 min

20 min

40 min

120 min

DR

I R

es

po

ns

e (

arb

itra

ry u

nit

s)

Retention volume (mL)

PS-L 257

360 min

240 min

20 22 24 26 28 30 32 34

0

1

2

3

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

1.358.60.33

1.8510.20.39

2.1611.10.42

2.4612.10.46

2.4912.30.47

2.5212.30.47

2.5312.40.48

Mw x 105

(g/mol)

R

(nm)

[]w

(dL/g)

1.358.60.33

1.8510.20.39

2.1611.10.42

2.4612.10.46

2.4912.30.47

2.5212.30.47

2.5312.40.48

Mw x 105

(g/mol)

R

(nm)

[]w

(dL/g)

0 min

5 min

10 min

20 min

40 min

120 min

DR

I R

es

po

ns

e (

arb

itra

ry u

nit

s)


PS-St3 85/255

240 min

20 22 24 26 28 30 32 34

0

1

2

3

4

1.827.10.20

1.908.10.21

1.998.40.22

2.018.40.22

2.038.50.22

2.048.50.22

Mw x 105

(g/mol)

R

(nm)

[]w

(dL/g)

1.827.10.20

1.908.10.21

1.998.40.22

2.018.40.22

2.038.50.22

2.048.50.22

Mw x 105

(g/mol)

R

(nm)

[]w

(dL/g)

0 min

10 min

20 min

40 min

120 min

240 min

DR

I R

es

po

ns

e (

arb

itra

ry u

nit

s)


PS-St8 25.3/202

AM Striegel, J. Biochem. Biophys. Methods 56 (2003) 117-139

Comparison 3: PS-L 447 vs. PS-St8 45.5/364


• PS-St8 45.5/364: 8-arm star PS ~364,000


0

1

2

3

4

5

20 22 24 26 28 30 32 34 36 38 40 42

0 min

5 min

10 min

360 min

20 min

DR

I R

es

po

ns

e (

arb

itra

ry u

nit

s)

40 min

120 min

240 min

600 min

PS-St8 45.5/364


[]w

(dL/g)

R

(nm)

Mw x 105

(g/mol)

0.38 13.0 3.81

0.36 12.6 3.58

0.36 12.3 3.40

0.34 11.5 2.97

0.33 11.1 2.84

0.31 9.9 2.24

0.27 8.4 1.66

0.24 7.2 1.11

0.22 6.2 0.73

20 22 24 26 28 30 32 34

0

1

2

3

0.887.10.26

1.348.70.32

3.0713.60.56

3.4814.80.62

4.0516.10.70

4.3216.40.73

4.4716.70.76

Mw x 105

(g/mol)

R

(nm)

[]w

(dL/g)

0.887.10.26

1.348.70.32

3.0713.60.56

3.4814.80.62

4.0516.10.70

4.3216.40.73

4.4716.70.76

Mw x 105

(g/mol)

R

(nm)

[]w

(dL/g)

0 min

5 min

10 min

20 min

40 min

DR

I R

es

po

ns

e (

arb

itra

ry u

nit

s)


120 min240 min

PS-L 447


Degradation of Linear vs. Star PS

• LCB appears to affect mechanism of degradation.

• Mechanism of degradation of high-M 8-arm star:

– Resembles degradation of intermediate-M 3-arm star more than it does degradation of intermediate-M 8-arm star.

• LCB effect on Mlim.

Revising the Definition of Mlim

• Need to include LCB effects on Mlim

• Propose (initially) that Mpath > Mlim

for ultrasonic degradation to occur.

“core”

“arm”

Marm » Mcore

If Marm > Mlim,

then degradation will occur

If Marm < Mlim, but 2Marm > Mlim,

then degradation will occur

But, if 2Marm < Mlim,

then no degradation occurs,

regardless of Mstar

Marm » Mcore

Marm < Mlim

Mlim 65 Kg/mol Marm 25.3 Kg/mol

2Marm Mlim

Mlim 65 Kg/mol 2Marm 50.6 Kg/mol

8Marm » Mlim

8Marm 202 Kg/molMlim 65 Kg/mol

Marm = 85.5 Kg/mol

2Marm = 171 Kg/mol » Mlim

20 22 24 26 28 30 32 34

0

1

2

3

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

0 min

5 min

10 min

20 min

40 min

120 min

DR

I Res

po

nse

(ar

bit

rary

un

its)


PS-St3 85/255

240 min

20 22 24 26 28 30 32 34

0

1

2

3

4

0 min

10 min

20 min

40 min

120 min

240 min

DR

I R

es

po

ns

e (

arb

itra

ry u

nit

s)


PS-St8 25.3/202



Definition #2

A continuous path of a given length must exist within a

polymer, such that, if Mpath > Mlim, the polymer will degrade

or

Given two polymers of the same chemistry and molar mass,

if Mpath1 > Mlim and Mpath 2 Mlim,

Polymer 1 will degrade, but Polymer 2 will not.


Monitoring Polymer Architecture

During Degradation

using

SEC/MALS/VISC/DRI

Polymer Conformation & Dimensionless Size

Radius of Gyration

31

10

3

AN

MR

i

cmiG Rrn

R2

1

1

.

Viscometric Radius

Random coil of homopolymers

Hard sphere

≈ 1.3

Rigid rod

0.3 – 0.4More extended

structure

More compact

structure

ri: location individual atom or group of atoms

Rcm: location of polymer center of mass

n: degree of polymerization

[]: intrinsic viscosity

M: molar mass

GR

R

Striegel, Yau, Kirkland, Bly, Modern Size-Exclusion Liquid Chromatography, 2nd ed. (Wiley, 2009)

Ultrasonic Degradation: Architectural Effects

0 60 120 180 240 300 360 420 480 540 600

0.6

0.7

0.8

0.9

zG

w

R

R

,

,

PS-L 65

PS-L 257

PS-L 447

Sonication time (min)


0 60 120 180 240 300 360 420 480 540 600

0.6

0.7

0.8

0.9

zG

w

R

R

,

,

PS-St3 85/255

PS-St8 25/202

PS-St8 46/364


Calculating Degradation Rate Constants

o

ntn

M

kk

tkMM

'

'11

0,,

Mn,t = Number-average molar mass (in g/mol) after

t min of sonication

Mn,0 = Number-average molar mass (in g/mol) of

unsonicated sample (i.e, at t = 0 min)

t = Sonication time (in min)

Mo = Molar mass of repeat unit (for PS, 104 g/mol)

k = Degradation rate constant (in min-1)

SL Malhotra, “Ultrasonic solution degradations of poly(alkyl methacrylates),”

J. Macromol. Sci.-Chem., A, 23 (1986) 729-748.

Plot 1/Mn,t vs. t to obtain k and, consequently, k

Effect of Molar Mass and

Architecture on Degradation Rate

Sample k (x 10-6 min-1)

PS-L 65 0.22 ± 0.00

PS-St8 9.8/78 No degradation observed

PS-L 257 2.12 ± 0.04

PS-St3 85/255 k1 = 0.87 ± 0.11 (0 - 20 min)

k2 = 2.36 ± 0.26 (40 - 240 min)

PS-St8 25.3/202 0.54 ± 0.02

PS-L 447 5.21 ± 0.30

PS-St8 45.5/364 k1 = 6.11 ± 1.07 (0 - 40 min)

k2 = 3.24 ± 0.19 (120 - 480 min)AM Striegel, J. Biochem. Biophys. Methods 56 (2003) 117-139

Influence of Chain Conformation on

Transient Elongational Flow

Degradation

SG Ostlund, AM Striegel. Polym. Degrad. Stab., 93 (2008) 1510

AM Striegel. Biomacromolecules, 8 (2007) 3944

Cellulose & Amylose

Structures

O

O

HO OH

O

HO

O

HO OH

HO

O

O

HO

O

OH

OH

O

HO

OH

OH( )n

mCellulose

-(14)

Amylose

-(14)

Ultrasonication of Cellulose & Amylose

Derivatives

• Hydroxypropyl cellulose in H2O, EtOH, & THF (Malhotra 1982).

• Nitrated cellulose in EtAc (Marx-Figini 1997).

• Hydroxyethylsulfoethyl cellulose, sulfoethyl cellulose, &

carboxymethylsulfoethyl cellulose and carboxymethyl starch in

H2O (Schittenhelm & Kulicke 2000).

• Hydroxyethyl cellulose in H2O (Xiuyuan et al. 2001).

• Methylhydroxyethyl cellulose in 0.1 M NaNO3 (Pfeferkorn et al.

2003).

• Carboxymethyl cellulose in H2O (Grönroos et al. 2004).

• No studies of non-derivatized cellulose or amylose.

Cellulose & Amylose

Molar Mass & Polydispersity

Sample Mn Mw Mz PDI

Cell 1 28,800 82,900 167,600 2.88

Cell 2 25,100 63,000 119,800 2.51

Cell 3 82,800 124,300 174,400 1.50

Cell 4 121,300 708,000 1,728,000 5.84

Amyl 1 83,400 148,300 245,600 1.78

Amyl 2 60,000 92,000 126,500 1.53

Data obtained using SEC/MALS, in DMAc/0.5% LiCl.

Mn, Mw, Mz in g/mol. PDI = Mw/Mn AM Striegel, Biomacromolecules, 8 (2007) 3944

Cellulose vs. Amylosea

104

105

106

0.0

0.5

1.0

1.5

2.0

Dif

fere

nti

al w

eig

ht

fra

cti

on

Molar mass (g/mol)

0 min

20 min

40 min

60 min

120 min

180 min

240 min

300 min

360 min

420 min

480 min

Amylose 1

aAmylose courtesy of Dr. Randy Shogren (USDA)

104

105

106

107

0.0

0.2

0.4

0.6

0.8

1.0

Dif

fere

nti

al w

eig

ht

fra

cti

on

Molar mass (g/mol)

0 min

40 min

120 min

180 min

420 min

780 min

Cellulose 4

AM Striegel, Biomacromolecules, 8 (2007) 3944

Mlim: Cellulose vs. Amylose

Mlim (g/mol)

Cellulose ~200,000

Amylose ~40,000


Degradation of Cellulose vs. Amylose

• Cellulose & amylose are both linear polymers.

• Both are composed of D-anhydroglucose repeat

units.

• Both are (14)-linked polysaccharides.

• Anomeric configuration:

O

O

HO OH

O

HO

O

HO OH

HO

O

O

HO

O

OH

OH

O

HO

OH

OH

in amylose In cellulose


• -(14) linked cellulose known to be

a stiffer (more “rod-like”) polymer than

-(1 4) linked amylose.

•

• REM: Path length effect.

)(5 limlim

amylosecellulose MM

Persistence Length, Lp

Lpr

Î1

nl

Ln

i

p as ,ˆˆ

11

11 I

I

The chains of stiffer (“rod-like”)

polymers “persist” for longer

in the direction of the first statistical

repeat unit than do the chains of

more flexible (“coil-like”) polymers.

I.e., a stiff, rod-like polymer will have

a longer persistence length Lp

than will a flexible, coil-like polymer.

We can determine the persistence

length Lp using SEC/MALS.

Persistence Length, Lp

M

ML

L

M

R

M Lp

p

L

G2

31

32/12/1

2

Lpr

Î1

2/1

2

GR

M

1/M

2/1)3(2

3LpL MLM

2/1

3

p

L

L

M

Lpcellulose = 55 3 nm

Lpamylose = 11 2 nm



•

•

)(5 limlim

amylosecellulose MM

)(5amylose

p

cellulose

p LL



Definition #3

For a polymer to degrade, a continuous path of a given length

and flexibility must exist within the polymer.

This path can be characterized by the persistence length, Lp,

so that:

Given two polymers of the same chemistry,


2

1

2

1

lim

lim

M

M

L

L

p

p

Ultrasonic Degradation: Architectural Effects

aAM Striegel, Biomacromolecules, 8 (2007) 3944; J. Biochem. Biophys. Methods, 56 (2003) 117bSG Ostlund, AM Striegel, Polym. Degrad. Stab., 93 (2008) 1510

Amylose

Cellulose

To

wa

rd m

ore

co

mp

act

str

uctu

re

0 100 200 300 400 500 600 700 800

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Linear Random Coil Polystyrene (in DMAc/LiCl)a

R

,w/R

G,z


Theoretical hard-sphere limit

PBLG (in DMAc/LiCl)b

CONCLUSIONS

• Macromolecular architecture affects mechanism of polymer

degradation in transient elongational flows.

• Have proposed a revised definition of Mlim that includes effects

of LCB and conformation on degradation.

• Results for degradation of rod-like polymers and copolymers

(random, block, and alternating) agree with proposed

mechanism.

• Ultrasonic laboratory studies: Can control experimental

parameters; require very little sample.

• Multi-detector SEC yields wealth of data related to architectural

and conformational effects on polymer degradation and

stability.

How Can Multi-Detector SEC Inform our Knowledge …...Striegel, Yau, Kirkland, Bly, Modern...

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