The Structure and Properties of Polymers

monomerpolymer

What is a polymer?

• A long molecule made up from lots of small molecules called monomers.

All the same monomer

• Monomers all same type (A)

• A + A + A + A • -A-A-A-A-• eg poly(ethene)

polychloroethene PVC

Different monomers – to form Copolymers

• Monomers of two different types A + B

• A + B + A + B -A-B-A-B-• eg polyamides • polyesters

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!

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.

The Structure of Polymers (plastics)

• 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 is carbon 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.

The Structure of Polymers (plastics)

• There are also some polymers that, instead of having a carbon backbone, have a silicon or phosphorous backbone and these are considered inorganic polymers.

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

Synthetic Polymers

• Commonly referred to as plastics – pliable, able to be moulded

• The bonding process. – When thermoplastic polymers are heated they become flexible.

There are no cross-links and the molecules can slide over each other.

– Thermosetting polymers do not soften when heated because molecules are crosslinked together and remain rigid.

Thermoplastics (80%)

• No cross links between chains.• Weak attractive forces between chains broken by

warming.• Change shape - can be remoulded.• Weak forces reform in new shape when cold.

Thermoplastics

• Those which soften on heating and then harden again 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

Thermosets

• Extensive cross-linking formed by covalent bonds.• Bonds prevent chains moving relative to each other. • What will the properties of this type of plastic be like?

Thermosetting

• Those which never soften once they have been 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

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.

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’

Addition Polymerisation

• 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

Hn

ethene

high pressure/trace O2

catalyst C C

H

H

H

H npoly(ethene)

Addition Polymerisation

• The polymer is the only product

• Involves the opening out of a double bond

• The conditions of the reaction can alter the properties of the polymer

• Reaction proceeds by a free radical mechanism

• Oxygen often used as the initiator

Addition polymerisation

C CH

H

H C

H

C C C

H H

H H H

Addition polymerisation

• Conditions are high pressure and an oxygen initiator (to provide the initial free radical).

• Monomer = phenylethene

• Polymer = poly(phenylethene)

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)

Review

• Work through the sample problem page 200

• Complete the revision questions page 200 (1 - 2)

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.

Linear polymers with side branches

• Isotactic– Same side of the linear

polymer– Greater effect of

dispersion forces therefore high density, rigid and tough and a high softening temp.

• Atactic– Irregular points on both

sides of the linear polymer– Chains of molecules cannot

get close together, therefore low density.

– Soft, waxy – little use

Poly(propene)

• This varying degree of randomness will affect the 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 Waal’s forces will be greater.

Linear polymers with cross links

• Cross links are covalent bonds that can form between 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 be produced.

Linear polymers with cross links

• To make a thermosetting polymer, the linear chains are produced first

• The cross linking is brought about either by heat or by adding a chemical to react between the lateral functional groups linking the chains together.

• Araldite is a good example of a two part glue – the 2nd method of producing a thermosetting polymer.

Condensation Polymers• Condensation polymerisation uses monomers that

have two functional groups per molecule.• These are said to be difunctional.• Polymerisation occurs when these monomers react

‘head-to-tail’ to form a new bond that will eventually join the monomers together

• A small molecule (often water) is eliminated

• condensation polymerisation simulation

Condensation Polymers

• Suitable functional groups

• -NH2 amine -OH alcohol

O O

• -C carboxyl -C acid chloride

OH Cl

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 linkage as in proteins).

• May be natural (protein, starch, cotton, wool, silk) or synthetic (viscose, nylon, polyester)

Polyesters

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

• The ester linkage is formed between the monomers

C

O

Othe ester linkage

Polyesters

• The structures of other polyesters

HO C

O

C

O

OHn + HO CH2 CH2 OHn

heat with an acid catalyst

C

O

C

O

O CH2 CH2 O

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

n

Polyamides

• These involve the linkage of two monomers through the amide linkage as in proteins (e.g. silk)

C

O

N

Hthe amide linkage

Nylon 6,6 a polyamide

N (CH2)6 NH

H

H

HC

O

OH(CH2)4

HO

OC

1,6-diaminohexane hexanedioic acid

N (CH2)6

H

N

H

C

O

(CH2)4 C

O

part of a nylon polymer chain

Kevlar a polyamide

NH2H2N CO

HO(CH2)4 C

O

OH

N N C (CH2)4 C

OO

H H

part of the kevlar polymer chain

Uses of polyamides

• The main use of polyesters and polyamides is as fibres in clothing.

• Most clothing now has a degree of manufactured fibres woven into the natural material (such as cotton).

• This gives the material more desirable characteristics, such as stretchiness, and better washability.

• Don’t forget that proteins are also polyamides, you must know how the linkage works with natural polymers such as proteins.

Review

• Complete the revision questions page 202 (3 – 5)

Commonly used polymersCommonly used polymers

• What would life be without polymers?• What would life be without polymers?

Addition PolymersAddition Polymers

• PVC, Teflon, Polystyrene – check table 9.1 page 198

• PVC, Teflon, Polystyrene – check table 9.1 page 198

Addition PolymersAddition Polymers• Ethene can be polymerised to produce

both low 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 – high density (plastic bottles)– Rigid, stronger and more opaque than LDPE– Slightly flexible, waxy surface that repels water

• Ethene can be polymerised to produce both low 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 – high density (plastic bottles)– Rigid, stronger and more opaque than LDPE– Slightly flexible, waxy surface that repels water

Addition PolymersAddition 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)

• 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)

Addition PolymersAddition 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

• 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

Condensation Polymers

• 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 and clothing industries.

Condensation Polymers• 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

Condensation Polymers• PET plastic Polyethene terephthalate.

– Soft drink bottles– An example of a polyester

– Note the removal of H2O (condensation polymer)

Polymer SelectionDue to their versatility, polymers can be

produced 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 substances that we rely on in today’s society.

This versatility can be attributed to the many different ways that they can be modified

Recycling Most plastics are

produced from crude oil, coal or gas.

Many of them are not biodegradable and have become a visible part of our environmental litter.

ReviewPolymers on line multiple choicePolymers quiz on lineComplete the multiple choice questions

pages 212, 213 (1 – 12)Complete the review questions 3, 6, 7, 9, 11,

13, 16, 19, 21