1. Polymers

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The Structure and Properties of

Polymers

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What is a polymer?

A long molecule made

up from lots of smallmolecules called

monomers.

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The Structure and Properties of

Polymers

monomerpolymer

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All the same monomer

Homopolymers Monomers all same

type (A)

A + A + A + A -A-A-A-A-

eg poly(ethene)

polychloroethene PVC

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Different monomers to form

Copolymers Monomers of two

different types A + B

A + B + A + B -A-B-A-B-

eg polyamides

polyesters

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Copolymerisation

when more than one monomer is used.

An irregular chain structure will result eg

propene/ethene/propene/propene/ethene

Why might polymers designers want to design

a polymer in this way?

(Hint) Intermolecular bonds!

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The Structure of Polymers (plastics)

Polymers are created by the chemical bonding

of many identical units . These polymers are

specifically made of small units bonded into

long chains. Carbon makes up the backbone of

the molecule and hydrogen atoms are bonded

along the carbon backbone.

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Polymers that contain primarily carbon and hydrogen are

classified as organic polymers. Polypropylene and

polystyrene are examples of these.

Even though the basic makeup of many polymers iscarbon and hydrogen, other elements can also be

involved. Oxygen, chlorine, fluorine, nitrogen, silicon,

phosphorous and sulfur are other elements that are found

in the molecular makeup of polymers. Polyvinyl chloride (PVC) contains chlorine.

Nylon contains nitrogen. Teflon contains fluorine.

Polyester and polycarbonates contain oxygen.

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There are also some polymers that, instead of

having a carbon backbone, have a silicon or

phosphorous backbone and these are

considered inorganic polymers.

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Natural Polymers

Wool, cotton, linen, hair, skin, nails, rubber,

and flesh are all naturally occurring polymers

Most naturally polymers are made of protein

or cellulose

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Synthetic Polymers

Commonly referred to as plastics pliable,

able to be moulded

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The bonding process.

When thermoplastic polymers are heated they becomeflexible. There are no cross-links and the molecules can slideover each other.

Thermosetting polymers do not soften when heated becausemolecules are crosslinked together and remain rigid.

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Thermoplastics (80%)

No cross links between chains.

Weak attractive forces between chains broken bywarming.

Change shape - can be remoulded.

Weak forces reform in new shape when cold.

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Thermoplastics

Those which soften on heating and then hardenagain on cooling

These are called thermoplastic polymers because they keep their plastic

properties

These polymer molecules consist of long chains which have only weak

bonds between the chains

The bonds between the chains are so weak that they can be broken when

the plastic is heated

The chains can then move around to form a different shape

The weak bonds reform when it is cooled and the

thermoplastic material keeps its new shape

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Thermosets

Extensive cross-linking formed by covalent bonds.

Bonds prevent chains moving relative to eachother.

What will the properties of this type of plastic belike?

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Thermosetting

Those which never soften once they havebeen moulded

These are called thermosetting polymers because once set

into a shape, that shape cannot be altered

These polymer molecules consist of long chains which have

many strong chemical bonds between the chains

The bonds between the chains are so strong that they cannot

be broken when the plastic is heated

This means that the thermosetting material always keeps its

shape

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Addition Polymerisation

When ethene is subjected to high pressure it changes from a

gas to a liquid

Liquid ethene (still under high pressure) is heated in the

presence of a catalyst (O2), an addition reaction takes place.

For addition polymerisation to occur, the monomer must have

a double C bond.

This bond breaks to allow the long chains to form.

Modifying ethene, substituting different functional groups for

hydrogen atoms produces other monomers that can be

polymerised to make polymers with different properties.

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Addition polymerisation

Monomers contain C=C bonds

Double bond opens to (link) bond to next

monomer molecule

Chain forms when same basic unit is repeated

over and over.

Modern polymers also developed based on

alkynes R-C C - R

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A carbon carbon double bond is needed in the

monomer

A monomer is the small molecule that makes up

the polymer

C CH

H

H

H

n

ethene

high pressure/trace O2catalyst

C CH

H

H

Hn

poly(ethene)

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The polymer is the onlyproduct

Involves the opening out of a double bond

The conditions of the reaction can alter theproperties of the polymer

Reaction proceeds by a free radical

mechanism

Oxygen often used as the initiator

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C CH

H

HC

H

C C C

H H

H H H

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Conditions are high pressure and an oxygen

initiator (to provide the initial free radical).

Monomer = phenylethene

Polymer = poly(phenylethene)

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Prediction the repeating unit

This is easy, basically open out the

double bond.

C C

H

H

Cl

H

chloroethene

C C C C

H H H H

H HCl Cl

poly(chloroethene) aka

polyvinylchloride (pvc)

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Linear polymers with side branches

Linear polymers are those in which the main

backbone is unbranched.

The way in which side branches are arranged

on linear polymers (polypropylene) can affect

the properties of the polymer.

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Linear polymers with side branches

Isotactic Same side of the linear

polymer

Greater effect ofdispersion forces thereforehigh density, rigid andtough and a high softeningtemp.

Atactic Irregular points on both sides

of the linear polymer

Chains of molecules cannotget close together, thereforelow density.

Soft, waxy little use

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Poly(propene)

This varying degree of randomness will affectthe strength and melting point of the polymer.

The less random, the stronger the polymer

and the higher the melting point This is because in a more ordered polymer

they chains can get closer together and hence

the van der Waals forces will be greater.

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Linear polymers with cross links

Cross links are covalent bonds that can formbetween polymer chains.

If the number of crosslinks is small an elastomer

(vulcanised rubber) will result. If the number of crosslinks is large a hard

inflexible thermosetting polymer will beproduced.

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Linear polymers with cross links

To make a thermosetting polymer, the linearchains are produced first

The cross linking is brought about either by

heat or by adding a chemical to react betweenthe lateral functional groups linking the chainstogether.

Araldite is a good example of a two part gluethe 2nd method of producing a thermosettingpolymer.

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Condensation Polymers Condensation polymerisation uses monomers

that have two functional groups per molecule.

These are said to be difunctional.

Polymerisation occurs when these monomersreact head-to-tail to form a new bond that will

eventually join the monomers together

A small molecule (often water) is eliminated

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Condensation Polymers

Suitable functional groups

-NH2 amine -OH alcohol

O O

-C carboxyl -C acid chloride

OH Cl

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Condensation Polymers Involves 2 monomers that have different functional

groups. They also involve the elimination of water or another

small molecule. Hence the term condensation polymer. Monomer A + Monomer B Polymer + small

molecule (normally water). Common condensation polymers include polyesters

(the ester linkage) and polyamides (the amide linkageas in proteins).

May be natural (protein, starch, cotton, wool, silk) or

synthetic (viscose, nylon, polyester)

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Polyesters

The OCR example here is terylene, a polymer ofbenzene-1,4-dicarboxylic acid and ethane-1,2-diol.

The ester linkage is formed between the monomers

C

O

O

the ester linkage

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Polyesters

The structures of other polyesters

HO C

O

C

O

OHn + HO CH2 CH2 OHn

heat withan acid

catalyst

C

O

C

O

O CH2 CH2 O

poly(ethan-1,2-diyl benzene-1,4-dicarboxylate)

n

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Polyamides

These involve the linkage of two monomers through

the amide linkage as in proteins (e.g. silk)

C

O

N

H

the amide linkage

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Nylon 6,6 a polyamide

N (CH2)6 N

H

H

H

H

C

O

OH

(CH2)4HO

O

C

1,6-diaminohexane hexanedioic acid

N (CH2)6

H

N

H

C

O

(CH2)4 C

O

part of a nylon polymer chain

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Kevlar a polyamide

NH2H2N C

O

HO

(CH2)4 C

O

OH

N N C (CH2)4 C

OO

H H

part of the kevlar polymer chain

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Uses of polyamides

The main use of polyesters and polyamides is asfibres in clothing.

Most clothing now has a degree of manufacturedfibres woven into the natural material (such as

cotton). This gives the material more desirable

characteristics, such as stretchiness, and betterwashability.

Dont forget that proteins are also polyamides, youmust know how the linkage works with naturalpolymers such as proteins.

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Addition Polymers

PVC, Teflon, Polystyrene

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Addition Polymers

Ethene can be polymerised to produce bothlow and high density polyethene

(commonly known as polyethylene)

LDPE produced with high temp and high pressure long

side chains low density (plastic bags) Soft, flexible and translucent with a waxy surface that repels

water.

HDPE produced with lower temp and pressure very few

short branches dispersion forces more effective highdensity (plastic bottles)

Rigid, stronger and more opaque than LDPE

Slightly flexible, waxy surface that repels water

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Addition Polymers

Rubber is an addition polymer that occurs

naturally

The monomer in natural rubber is isoprene.

It polymerises to form long chains.

Molecular formula (C5H8)n

Rubber still contains double bonds which

can be attacked by oxygen and can perish

(unlike polythene)

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Addition Polymers

Rubber

not elastic long chains straighten out when stretched

and remain this way

Susceptible to temperature changes brittle when cold

and sticky when hot.

Vulcanisation improved durability and elasticity of

rubber.

The linear chains are cross linked using heat and sulfur

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Nylon

Can be extruded when molten to form fibres or

sheets of strong, durable and elastic material

Its invention had a great impact on the textile andclothing industries.

C d i l

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Nylon 6 : 6

Nylon is a linear chain containing up to 100

repeated units.

The name nylon 6 : 6 refers to the existence of

6 carbon atoms on each of the units

C d i P l

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Condensation Polymers PET plastic Polyethene terephthalate.

Soft drink bottles An example of a polyester

Note the removal of H2O (condensation polymer)

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Polymer Selection

Due to their versatility, polymers can beproduced for almost any imagined purpose.

A huge range of polymers exist today and are

used for many different applications. Their versatility has made them one of them

one of the most useful classes of substancesthat we rely on in todays society.

This versatility can be attributed to the manydifferent ways that they can be modified

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Recycling

Most plastics areproduced from crudeoil, coal or gas.

Many of them are notbiodegradable and

have become a visiblepart of ourenvironmental litter.

Documents

1. Polymers