Chapter 14Polymers

Introduction

Polymers are composed of enormous molecules containing anywhere from

thousands to heptillions (1024) of atoms per molecule. Molecules which are this large are

called "macromolecules."

Some macromolecules have a variety of different types of atoms connected together

willy-nilly without much apparent order (coal).

Some macromolecules made of only one or two types of atoms which are bonded

together in simple exact 3-D crystalline structures (diamond or quartz).

Polymers are macromolecules which have situation in between simple crystals and

haphazard structures.

Although they may contain millions of atoms, these millions of atoms are typically

organized as repeating patterns of smaller groups of atoms, known as "monomer units," which are all covalently bonded together one

after another like railroad cars in a train.

Monomer units themselves typically contain a group of from two to fifty atoms bonded to

one another in well-defined covalent structures.

If you look at the structural formula for a molecule and notice same pattern of atoms

and bonds repeats itself over and over again, then you are looking at the structural

formula for a polymer.

Plastic, hair, wood, muscle, rubber, starch, DNA, nylon, cotton, and dacron are all

polymers; some are man-made and some are "natural."

Organic Chemistry

In order to understand polymers (both natural and man-made) it is first necessary to

understand a little more about organic chemistry. Most polymers are organic

chemicals (especially natural ones).

Organic chemicals are chemicals with molecules (or macromolecules) which are

made of carbon atoms covalently bonded to other carbon atoms (catenation) and/or several other kinds of atoms. The atoms

which are found in organic (macro)molecules live in the upper right portion of the Periodic

Table (the "nonmetals"), plus hydrogen.

Fossil fuels are all organic chemicals.

Almost all organic chemicals made from fossil fuels (exceptions: small quantities

complicated drugs sometimes obtained from plants or bacteria).

In recent past virtually all manmade organic chemicals obtained from petroleum

("petrochemicals"). Today, however, technology exists for making complete set of

organic chemicals from coal (via gateway chemical methanol).

Fossil fuel first broken down with catalysts and heat ("cracked"), then converted to

alkenes & alkynes (petroleum), or aromatics (coal or petroleum) with appropriate

catalysts.

These "feedstocks" then turned into blistering array of different organic

chemicals by techniques known as "organic synthesis."

In past light alkene & alkyne feedstocks only made from petroleum. Now make from coal via methanol or methane (coal gasification).

VALENCES

The valences (number of attached bonds) of each of the common organic atoms are given

in table below.

Atom Attached BondsB 3Al 3C 4Si 4N 3P 3 or 5O 2S 2, 4, or 6F 1Cl 1Br 1I 1H 1

FUNCTIONAL GROUPS

Certain particular combinations of atoms are found so often in organic chemicals that they are given special names. The structures of

these "functional groups" and names of classes of molecules containing them given in

Table 14.3 on pg. 415.

The beauty of functional groups is that over the centuries organic chemists have figured out how to use inorganic chemicals (don't

need to obtain from fossil fuels) to interconvert them into one another.

Double bonds, triple bonds, and aromatic rings (not shown on table) are functional

groups. Once you have created these from fossil fuels you can go wild and make

anything you want. The science of interconverting functional groups into one

another is known as organic synthesis.

ALPHA CARBON

Any organic molecule is simply a hydrocarbon chain (linear, branched, or containing rings) with functional groups

attached at various places. The carbon atom of a hydrocarbon chain to which functional group is attached is called an alpha carbon. Alpha carbon is not part of functional group

(ie. carboxylic acid or alkene carbons).

Hydrogens attached to an alpha carbon are called alpha hydrogens.

Functional groups often classified according to how many hydrocarbon branches are attached to their alpha carbon. If alpha

carbon is attached to one other carbon (not including functional group carbons),

functional group and alpha carbon called primary (1). If alpha carbon has two carbon

neighbors term secondary (2) used; three neighbors called tertiary (3).

PROPERTIES & REACTIONS OF SOME FUNCTIONAL GROUPS

Reactions of Hydrocarbons

Addition. Must have multiple bonds. Two molecules combine to make one molecule.

Triple forms double and double forms single bond.

C CHH

H

HH

Cl

+ HClC CH

H H

H

C CHH

Cl

HH

Cl+ ClClC C

H

H H

H

C CHH

H

HH

H+ HHC C

H

H H

H

CH CH CH2 CH2 CH3 CH3

H2 H2

Substitution. Two molecules react, rearrange fragments, and form two different molecules. Parts of original molecules "swap partners."

C CHH

H

HH

ClCl2+C CH

H

H

HH

HHCl+UV

light

Combustion. Hydrocarbon molecule reacts completely with oxygen during combustion

(burning) to make several molecules of carbon dioxide and water.

7 O2+C CHH

H

HH

H2 4 CO2 + 6 H2O

Properties & Reactions of Alcohols

Alcohols classified as primary, secondary, or tertiary according to how many carbon

neighbors their alpha carbon has. Methanol (CH

3OH) is a 0 alcohol because its alpha

carbon has no carbon neighbors. Ethanol (CH

3CH

2OH) is a primary alcohol.

Idiosyncratic terminology involving alcohols: "proof" ratings, "denaturing," and

commonly-used names of ordinary every-day alcohols. Other issues: hydrogen bonding (very important) and organic chemistry of

alcohols.

Proof Ratings.

Ethanol and water mixture (booze) will burn if the amount of ethanol in the mixture is

higher than 50%. Back before turn of

century flammability used as "proof" of strength of booze.

Pure ethanol is what proof?Since 50% ethanol will burn, it is said to be "100 proof." Therefore the proof rating is simply double the purity. 100% ethanol is

200 proof.

Denaturing Alcohol.

During prohibition in the US ethanol could not be made completely illegal because it was useful as a solvent for industrial and research purposes. In order to discourage people from

drinking lab alcohol back then the government required that all lab alcohol be

contaminated with enough methanol to make people go blind if they drank it (the origin of

the phrase "blind drunk"). Since it is the "nature" of ethanol to make you drunk

without losing your eyesight, the process of contaminating lab ethanol with methanol was called "denaturing" it. "Denatured" ethanol can still be found but not very common now.

Common Names of Alcohols.

CH3OHmethanolmethyl alcoholwood alcohol

2-propanolisopropyl alcoholrubbing alcohol

CH2CH2OH OH

CH3CHCH3OH

1,2-ethanediolethylene glycol

CH2CHCH2OH OH OH1,2,3-propanetriolglycerolglycerin

CH3CH2OHethanolethyl alcoholgrain alcohol

Origins of common names: Wood alcohol (methanol) originally distilled from

hardwood, ethylene glycol (1,2-ethanediol) alcohol made from ethylene which tastes sweet ("glyco" usually refers to sugar, ie.

"glycolysis), grain alcohol (ethanol) originally distilled from fermented grain, rubbing

alcohol (2-propanol) rubbed on body to kill bacteria and ease fever, glycerol (1,2,3-

propanetriol) like (ethylene) "glycol" but needed modified word.

Hydrogen Bonding in Alcohols.

A hydrogen bond is a weak temporary bond formed between a hydrogen atom attached to nitrogen, oxygen, or fluorine (electronegative

atom which sucks away electron material from hydrogen leaving it positive charged

and hungry for electrons) and a nonbonding pair of electrons belonging to a different

nitrogen or oxygen atom.

::H H

O

::CH3 H

O::

H CH3

O

donor

acceptors

A water molecule can form two hydrogen bonds because it has two hydrogen atoms

capable of participating in this type of bonding.

Most alcohols can form only one hydrogen bond. Important exceptions:

OH

CH2 CH2

OH OH

CH2 CH

OH

CH2

OHethylene glycol:two hydrogenbonds per molecule

glycerol: threehydrogen bondsper molecule

When we talk about how many hydrogen bonds a molecule can form we are talking

about how many hydrogens it has capable of being "donors."

The more hydrogen bonds a molecule can form the more strongly it sticks to water &

other molecules like itself.

Alcohols having less than 4 carbons are all totally water-soluble because the alcohol molecules stick well to water molecules.

Alcohols with 4 or more carbons become less and less water-soluble because their hydrocarbon parts are "oily" (oil is

hydrocarbon and oil and water don't mix).

Balancing act between "hydrophobic" carbon fragment and "hydrophilic"

hydrogen-bonding OH piece determines water solubility. Soluble as long as there are

at least 1/3 as many OH's as C atoms.

Sucrose (table sugar) is water-soluble even though it has 12 carbons because it has 8 OH groups capable of forming hydrogen bonds.

The more hydrogen bonds a molecule can form the stronger this hydrogen bonding is

and the harder it is to separate these molecules from one another. More heat has

to be added to change substance whose molecules stick together tenaciously from

liquid into gas (high boiling point).

Hydrogen bonding in alcohols makes alcohols good anti-freeze agents. Liquids

contaminated with very soluble impurities are hard to boil or freeze. The most effective

anti-freeze agents are nonvolatile (ie. salt) and have low molecular weights.

Although table salt is better at keeping water from freezing or boiling than most alcohols

(low molecular weight and completely nonvolatile), brine solutions are corrosive to

metal surfaces (engines) whereas alcohol solutions are not.

Ethylene glycol (1,2-ethanediol) is the best compromise for an alcohol antifreeze. It can

form two hydrogen bonds which gives it a high boiling point (nonvolatile) and it has a reasonably low molecular weight (62 g/mol vs. average molecular weight of about 29

g/mol for the ions in table salt).

Organic Chemistry of Alcohols.

For this course need to know oxidation of alcohols, hydration of alkenes to make alcohols, and reaction of alcohols with

carboxylic acids to make esters.

CH2 CH2

CH2 CH2

OHHheatpressurecatalystethylene ethanol

Hydration of an alkene to make an alcohol. An addition reaction.

H OH+water

CH3CH2OH CH3 CH

O

CH3 C OH

O

LAD enzyme

ethanoic acid"acetic" acid (vinegar)

Oxidation of ethanol to ethanal (commonname acetaldehyde) by liver enzyme or to acetic acid by Cr(VI) in breathalyzer test.

+ Cr(III)

Cr(VI)

or Cr(VI)ethanol ethanal

(an aldehyde)

CH3CH2 OH O C

O

CH3H+

CH3CH2 O CO

CH3

ethanol(ethyl alcohol) acetic acid

ethyl acetate

ethyl alcohol + acetic acid = ethyl acetate

Ester naming: drop "alcohol" fromalcohol name, drop "ic acid" fromcarboxylic acid name, then add"ate" ester suffix.

HOH +

Water (HOH) is byproduct of this substitution reaction. The majority of substitution reactions you will see in remainder of this course involve two

molecules coming together to form a third molecule after a molecule of water is

removed. Esterification reaction is merely one example of this.

Aldehydes and Ketones

Aldehydes and ketones not as important as alcohols in fuel chemistry, making polymers,

and biochemistry. Important thing to understand is difference between them.

Both aldehyde and ketone molecules contain a molecular fragment called a "carbonyl

group" which made from an oxygen atom connected to a carbon atom with two bonds.

C

O

carbonyl group

Remember that oxygen likes two bonds and carbon likes four bonds. Oxygen is satisfied here but carbon needs two more neighbors.

If both neighbors are carbons, molecule is a "ketone." If neighbors are C & H or H & H,

molecule is an "aldehyde."

Carboxylic Acids

Like aldehydes and ketones carboxylic acid molecules also have carbonyl groups. If one of carbonyl carbon's two other neighbors is

hydroxide (OH) then molecule called "carboxylic acid."

Unlike aldehydes and ketones carboxylic acids very important in polymer chemistry

and biochemistry.Two most important reactions to learn

involving carboxylic acids are conversion of carboxylic acids into esters and amides.

Reactions which make esters and amides from carboxylic acids are substitution

reactions which involve creation of water molecules as byproducts.

Substitution reactions used to make polymers called "condensation" reactions

("condensed" milk is milk which has had water removed from it).

CH3 C

O

OH O CH3H

CH3 C

O

O CH3

+

+ HOH

carboxylic acid alcohol

ester water

CH3 C

O

OH N CH3H

H

+

+ HOH

carboxylic acid amine

amide waterN

H

CH3 C

OCH3

Esters, Amides, and Anhydrides

These are three more classes of organic compounds which contain the carbonyl group. They have the atom connection

patterns shown below.

ORGANIC CHEMICALS FROM COAL

Show Fig. 14.3

Polymers

Remember that polymers are made of repeating "monomer units" (small molecular fragments) linked together one after another

like railroad cars in a train.

CATEGORIZING POLYMERS

there are three different ways of categorizing polymers: The kind of chemical reaction used

to make them, the manufacturer (man or nature), and the kind of structure the

polymer has.

Chemistry.

Polymers can be made by three general types of chemical reactions.

"Addition" polymers are made by combining monomer molecules via addition reactions.

All of the atoms originally present in the monomer molecules retained in polymer

(2+2=4).

"Condensation" polymers (involves reduction of total number of atoms) are made

by substitution reactions.

When a monomer molecule reacts with a developing polymer molecule a removable

fragment attached to monomer leaves along with a removable fragment attached to

growing polymer. This leaves both monomer and growing polymer bereft of partners; they

attach to one another.

Condensation polymers give small-molecule byproducts (two removed functional groups

combined) when synthesized (8+12=17 polymer atoms).

"Rearrangment" polymers are made when a monomer molecule attaches to a growing polymer molecule and then one or more

atoms attached to the polymer decide they are unhappy where they are and have to jump around to different locations on the polymer before the situation can stabilize.

PROBLEM 41.What common to all condensation rxns?

@ A small molecule is eliminated.

Manufacturer

Polymers are called "synthetic" if they are made by man and "natural" if they are made

by nature. Man often makes identical polymers to nature. In this case the synthetic

polymers are indistinguishable from the natural polymers. Nature uses the same

three basic kinds of chemical rxns outlined above to make polymers that man does.

Structure

Polymers are categorized according to structure by two different criteria, molecular

shape and arrangement of monomer units

Molecular Shape.

Polymers whose monomer units are attached to one another like railroad cars have a shape

like very long strands of spaghetti, or like string. Polymers with this kind of structure

called "linear" polymers.

Another kind of architecture exists for polymers. Many polymers built like lots of separate strands of string laid side by side and then connected together at multiple

places to give structures looking like fishing nets. These polymers said to be

"crosslinked." Connections between strands = "crosslinks."

Arrangement of Monomer Units.

Polymers made of only one kind of monomer unit called "homopolymers" ("homo" means

same).

Polymers made up of two or more different kinds of monomer units called "copolymers"

("co" means in collaboration with).

ADDITION POLYMERS

"Addition" polymers made by addition reactions. Monomers are alkenes (double bond necessary). Total number atoms in

polymer can be calculated by simple addition of atoms in monomers.

PROBLEM 24.What structural feature do all addition

monomers share?@ They are all alkenes

Show Table 14.10

In general a monomer must have at least two reactive sites (places where covalent bonds

can form) in order to be able to become part of a polymer. This because each monomer must attach to two other monomers (one in

front and one behind) to become part of polymer. Polymers have monomer units

arranged like railroad cars in a train.

One C-C double bond contains two reactive sites (one at each C atom). This because

when second C-C bond in alkene is broken each carbon can is now free to bond to

another alkene monomer unit (M).

C C C C

M M

2 M

Remember: carbon has 4 "sticks"!

Addition Polymerization Mechanism

First an unstable reactive molecular fragment is created which has one atom

which is devoid of a partner (doesn't have enough bonds to neighbors to be happy).

This fragment either a "free radical," "cation," or "anion" based on the charge

held by the unhappy atom.

Next the unhappy atom finds the alkene part of an addition monomer molecule. It breaks

the second bond of the C-C double bond, attaches itself to one of the two carbons, and leaves the other carbon devoid of a partner

(unhappy).

The unhappy carbon atom finds the alkene portion of a second monomer molecule,

breaks the second bond of the C-C double bond, attaches itself to one of the two alkene

carbons, and leaves the second carbon to fend for itself (unhappy). This process

repeats self indefinitely till polymer created.

Read text page 428.

Recognizing Addition Polymers

If main chain of polymer contains only catenated carbon atoms polymer was made by addition reaction. If main chain contains other atoms (O, N, Si, P) then polymer made by substitution reactions and is condensation

polymer.

CH CH2 CH CH2 CH CH2 CH

polystyrene

CH2 CH

CN

CH2 CH

CN

CH2 CH

CN

CH2 CH

CN

CH2 CHCl

CH2 CHCl

CH2 CH

Cl

CH2 CH

Cl

polyacrylonitrile

polyvinylchloride (PVC)

To figure out what monomer an addition polymer was made from first draw a box around any two carbon atoms in the main chain and include any functional groups attached to either of these carbons. Next

erase everything outside of the box you drew. Finally make a double bond between the two

main-chain carbons. Remove the prefix "poly" from the polymer name to make

monomer name.

CH CH2 CH CH2 CH CH2 CH

polystyreneCH2 CH

styrene

PROBLEM 34.Determine monomer Orlon made from.

@ "Orlon" is a trade name for polyacrylonitrile.

CH2 CH

CN

CH2 CH

CN

CH2 CH

CN

CH2 CH

CNpolyacrylonitrile

CH2 CH

CNacrylonitrile

CROSSLINKING

Polymers that have many crosslinks between linear chains result in a structure resembling

either a fishing net, or, more often, a 3-D crosslinked "honeycomb" structure which

more closely resembles a block of Swiss cheese.

Process of crosslinking polymers started with "vulcanizing" of rubber discovered

accidentally by Goodyear in 1839 (p. 434 of text).

In order for a polymer to form crosslinks at least one of the monomers used to make it

must have more than two reactive sites. Two reactive sites per monomer are needed like

couplers on railroad cars to produce an linear polymer with no crosslinks. Extra

reactive sites from different linear chains can be connected (forming crosslinks) bringing

many different linear chains together in crosslinked structure.

RUBBER

Rubber is an addition polymer made from a monomer called "isoprene."

CH2 C

CH3

CH CH2isoprene

Notice that isoprene has two double bonds and it only needs one to form a linear

polymer. When this monomer is polymerized the carbons on the left-hand side and the right-hand side become the reactive sites, both double bonds are broken, and a new

double bond forms between the two carbons in the center. The net result is that one double bond is used in making linear

polymer, and one double bond remains, but has moved to center of molecule.

Show rubber from isoprene.

Read text p. 434 - 436 about rubber.

Nature makes two different addition polymers out of isoprene which have a subtle

structure difference but different material properties.

Nature doesn't crosslink linear isoprene polymers via extra alkene carbons after

doing polymerization. Therefore the natural linear isoprene polymers still have extra C-C

double bonds (at every fourth position in polymer chain).

If these double bonds have polymer chain running through them in a cis fashion then the polyisoprene is called "natural rubber."

If the extra double bonds have polymer chain running through them in trans fashion then

the polyisoprene called "gutta-percha."

Since 1839 (Charles Goodyear) natural rubber (cis) has had some of extra alkene

carbons crosslinked together with sulfur by melting rubber and sulfur together to make rubber for car tires, etc. Crosslinked gutta-percha used for golf ball covers & electrical

insulation.

PROBLEM 27.

Sketch & describe properties of cis & trans polyisoprene.

SSS S S

S

SSS

S S S

CH3

CH3

CH3

CH3CH3

CH3

CH3

CH3CH3

CH3

CH3

CH3

Vulcanized natural rubber

PROBLEM 28.Describe the role of sulfur in vulcanization.

@ Forms crosslinks.

PROBLEM 29.Effect of vulcanization on physical properties

of rubber?@ Makes rubber high melting, stretchable,

and tough rather than gooey.

PROBLEM 30.Describe nature of polymer which is

extensively crosslinked (small rings like diamond structure).@ Hard and brittle.

PROBLEM 35.Which monomers can undergo addition

polymerization and why?@ a. Styrene. Yes. Has alkene group.

b. Propene. Yes. Also is an alkene.

c. Ethane. No.Not an alkene.

THERMOSETTING POLYMERS

Because crosslinking a polymer holds its macromolecules together better, these

polymers are tougher, stiffer, more resilient, more heat resistant, harder to tear, higher melting, and longer lasting than ordinary

polymers.

If a polymer is an oily liquid before crosslinking, it will probably become a

rubbery stretchable solid afterwards. If a polymer is a low-melting solid plastic before crosslinking, it will probably become a rock-

hard, brittle ceramic-like material after crosslinking.

Some polymers become crosslinked while the monomer molecules are reacting with one another but most are formed in two steps.

First step in forming two-step crosslinked polymers involves making linear polymer

with excess unreacted reactive sites (removable fragments in condensation monomers or double bonds in addition

monomers).

Linear polymer formed in first step is solid; too stiff to enable excess reactive sites to be

able to find each other & make crosslinks till polymer is melted.

Second step: When a solid condensation polymer with excess reactive sites is heated, it

melts, enabling the excess reactive sites to move around and find each other, forming crosslinks. Once the crosslinks form the polymer solidifies and will not melt again

even when heated.

This crosslinking process is called "thermosetting" (thermo = heat, setting = stiffening). Ordinary linear polymers with

no excess reactive sites cannot be thermoset.

When they are heated they just melt and never stiffen up.

For this reason ordinary polymers are called "thermoplastic" rather than thermosetting

("plastic" means soft or workable; thermoplastics become soft or melt when

heated).

Addition polymers normally cannot be crosslinked without the help of added

vulcanizing agents (sulfur in rubber) which form the crosslinks.

Alkene carbons not reactive enough to form bonds to one another just by melting the

polymer (this is why an initiator needed to start addition polymerization rxns).

Special crosslinking agents (sulfur in rubber) need to be added to the melted addition polymer to connect together the excess

reactive sites (alkene carbons) and form crosslinks.

The more extensively crosslinked a polymer is (small ring sizes, tight weave or mesh) the

more brittle a polymer becomes.

Remember diamond is made of interlocking 6-membered rings, whereas in rubber the

ring sizes can be as large as several hundred atoms, depending on how thoroughly

vulcanized the rubber is.

CONDENSATION POLYMERS

Formed by removal of fragments of functional groups from two or more different kinds of monomers, which allows monomers to bond to one another and generates small-molecule byproducts composed of fragments

removed from monomer molecules.

If they can crosslink normally they are thermosetting; they generally solidify before

they can crosslink completely.

C C

OO

OHOH CH2 CH2 OHOH

C C

OO

OHOH CH2 CH2 NH2NH2

CO

OH

CO

OH

CH2

CH

CH2

OH

OH

OH

SiOH OH

CH3

CH3

SiOH OH

CH3

OH

+

+

+polyesters

polyamides

alkyd

silicone rubber

silicone oil

OH

C O

C O

OH

O

CH2

O

H

H

CH2

OH

C O

C O

OH

OH

C O

C O

OH

C O

C O

O

CH2

O

CH2

O

HOH

HOH

HOH

Polyester formation

OH

C O

C O

OH

N

CH2

N

H H

H HOH

C O

C O

OH

NHH

C O

C O

N

OH

C O

C O

N

CH2

H

H

N H

HOH

HOH

HOH

Polyamide (Nylon) formation

CO

O

C

O

OH

H

CO

O

C

O

O

H

H

CO

O

C

O

O

H

H

CO

O

CO

OH

H

CH2 CH CH2

OH OH

OH

CH2 CH CH2

OH OH

OH

CH2 CH CH2

OH OH

OH alkydformation

OH

Si

O

CH3CH3

H

OH

Si

O

CH3CH3

H

OH

Si

O

CH3CH3

H

OH

Si

O

CH3CH3

H

Si

O

CH3CH3

O

OH

Si CH3CH3

Si

O

CH3CH3

Si

O

CH3CH3

H siliconeformation

Polyesters

Usually made from diacids and dialcohols condensed together. Major uses: clothing

and plastic bottles.

Polyamides

Also called Nylons. Made from diamines and diacids. Extremely strong because hydrogen

bonding creates pseudocrosslinks. Most commonly known Nylon is Nylon 66 made

from adipic acid and hexanediamine. Called Nylon 66 because the diacid (adipic acid) and

the diamine each have 6 carbons.

PROBLEM 42Starting materials for Nylon 66?

@ adipic acid and hexanediamine

Show non-ball-and-stick version of Fig. 14.12 with H bonds acting like pseudocrosslinks in

Nylon 6.

Alkyds

Like polyesters except that glycerol (a triol) used rather than a diol. Since the alcohol

monomer has more than two (3) reactive sites (alcohol functional groups) a crosslinked

polymer is formed. Used for tough factory paint jobs for cars (Fact-O-Bake). Final step requires baking because the polymer needs to

be melted to allow it to make all of its crosslinks (thermosetting).

Silicones

Formed by reacting chlorosilanes (have chlorine atoms bonded to silicon atoms) with

water. Initially OH group from water replaces all chlorines attached to silicon.

SiOH groups not stable- SiOSiOSiOSiOSiOSiOSiOSi polymers

form by loss of waters. Each OH attached initially to a silicon is a reactive site.

If monomer starts with only two OH groups attached to silicon a linear polymer produced which is an oil. If monomer starts with three OH groups bonded to silicon crosslinks can

form, so resulting polymer is a thermosetting tough rubbery solid called silicone rubber. If

monomer starts with four OH groups attached to silicon sand is produced.

Generally this is only done to produce a superfine sand called silica gel.

Silly Putty is produced from a mixture of diclorosilanes (produces two OH groups attached to each Si) and trichlorosilanes (three OH groups per Si). The resulting

polymer has properties midway between oil (linear polymer) and silicone rubber

(crosslinked tough rubbery polymer). Not a liquid oil but you can pull it apart; mushy,

yet you can bounce it.

Silicone rubber much more heat-stable than isoprene rubber because Si-O bonds are

extremely strong.

PROBLEM 32.Show how polymers prepared from

monomers given.@:

a. CH3CH=CHCH

3 addition with self makes

poly-2-butene

b. HOOCCH2CH

2COOH condensation with

dialcohol makes polyester.

b. HOOCCH2CH

2COOH condensation with

diamine makes polyamide (or nylon).

c. H2NCH

2CH

2CH

2CH

2NH

2 condensation

with diacid makes polyamide (nylon).

d. (CH3)2Si(OH)

2 condensation with self

makes silicone oil (remember the rubber needs 3 OH groups attached to Si so crosslinking can happen).