Slides - Unit 18

Unit 18

Polymers

18.1
Introducing Polymers

Learning objective: polymer,
synthetic
■ Explain the terms of monomer,
polymerisation, natural polymer and
polymer.

What are Polymers:

1. Polymers are large molecules built up from
small units called monomers.

polymer

2. Monomers are linked together by strong
covalent bonds to form polymers.

3. Polymers can be:
i. synthetic (e.g. polyethene, PVC) or
ii. natural (e.g. protein, carbohydrate).

4. Polymers are made by two kinds of
polymerisation reactions:

i. addition polymerisation

ii. condensation polymerisation

Synthetic polymers:

Monomer Polymer Form by … Use

ethene poly(ethene) addition polymerisation plastic shopping bags and drink
propene poly(propene) addition polymerisation bottles

buckets, crates and ropes

phenylethene / poly(phenylethene) / addition polymerisation insulation and protective packaging
styrene poly(styrene) addition polymerisation
water pipes and insulation on
chloroethene poly(chloroethene) / electric cables
polyvinyl chloride
1,6- (PVC) condensation polymerisation nylon fibres are woven into fabric
diaminohexan for clothing
and hexan-1,6- polyamide,
dioyl chloride e.g. nylon condensation polymerisation polyester fibres are woven into
benzene-1,4- fabric for clothing
polyester,
dicarboxylic e.g. Terylene
acid and

ethane-1,2-diol

18.2
Addition Polymerisation

Learning objectives:
■ Describe addition polymerisation.
■ Name at least three polymers formed by addition

polymerisation, and give uses for them.
■ Draw a labelled diagram to show the addition

polymerisation of ethene to make polyethene.

Addition polymerisation:

1. In addition polymerisation, the monomers are
identical to each other.

2. The identical monomers are linked next to one
another by the breaking of the C=C double
bonds in the monomers.

3. The monomers can be repeated any number
of times and added together to form only one
product (the polymer).

4. The polymers formed has single bonds.

Addition polymerisation:

double
bond

(m(ponlyommeerr))

Example 1: 1. Poly(ethene) is the most common type of
synthetic polymers.
Poly(ethene)
2. Properties of polyethene:
■ light
■ bends without breaking
■ tough
■ water-resistant

3. Plastic bags and cups are made from
poly(ethene).

4. Poly(ethene) is made up of many ethene
monomers.

Formation of poly(ethene) by addition polymerisation:

++ +

(ethene) (ethene) (ethene)

(polymer)

The ethene monomers link together to form a long chain poly(ethene).
They do this by opening up their double C=C bonds.

A simple way of writing the polymer structure for polyethene is:

(repeat unit)

Example 2: 1. Poly(chloroethene) is also known as
polyvinyl chloride (PVC).
Poly(chloroethene)
2. Properties of poly(chloroethene):
■ flexible
■ good insulator
■ easily moulded
■ water-resistant

3. Waterproof clothing, covering for
electrical wiring, dustbins, table, chairs
are made from poly(chloroethene).

4. Poly(chloroethene) is made up of many
chloroethene monomers.



A simple way of writing the polymer structure for poly(chloroethene) is:

Drawing the polymers:

Example:
Monomer: phenylethene (or styrene)
1. Draw three monomer units (arranged

vertically) with their double bonds next to
each other.

C6H5 H C6H5 H C6H5 H

CCCCCC

HHHHHH

Drawing the polymers:

Example:
Monomer: phenylethene (or styrene)
2. Change the C=C double bonds to C-C single

bonds.

C6H5 H C6H5 H C6H5 H

CCCCCC

Polymer: H H H H H H
Poly(phenylethene) or poly(styrene)

Drawing the polymers:

Example:
Monomer: phenylethene (or styrene)
3. Draw a C-C single bond between the

repeat units.

C6H5 H C6H5 H C6H5 H

CCCCCC

Polymer: H H H H H H
Poly(phenylethene) or poly(styrene)

Drawing the polymers:

Example:
Monomer: phenylethene (or styrene)
4. Put ‘continuation bonds’ at both ends of

the chain.

C6H5 H C6H5 H C6H5 H

CCCCCC

Polymer: H H H H H H
Poly(phenylethene) or poly(styrene)

Alternative way:

1. Draw the structure of a monomer.
2. Change the C=C double bond to a C-C single bond.
3. Put ‘continuation bonds’ at both ends of the repeat unit.
4. Put square brackets through the continuation bonds.
5. Put an ‘n’ at the bottom right to show a large number of repeat units.

The ‘n’ in front C6H5 H C6H5 H
of the monomer nC C CC
shows that there
HH
are a large
number of them. monomer

HH n

polymer

Identify the monomers from the polymers:

Example:
Polymer: poly(propene)
1. Identify the repeating unit in the polymer.

CH3 H CH3 H CH3 H
CC CC CC

HHHHHH

Identify the monomers from the polymers:

Example:

Polymer: poly(propene)

2. Draw this repeating unit as a separate
molecule and remove the ‘continuation
bonds’.

CH3 H

CC

Monomer: HH
propene

Identify the monomers from the polymers:

Example:

Polymer: poly(propene)

3. Make the C-C single bond into a C=C
double bond.

Monomer: CH3 H
propene CC
HH

18.3
Condensation
Polymerisation

Learning objectives:
■ Describe condensation polymerisation.
■ Draw simple diagrams to show the monomers, and

part of the polymers molecule for nylon and Terylene.
■ Explain what the amide and ester linkages are, and

identify them on a drawing.
■ Give uses for nylon and Terylene.

Condensation Polymerisation:

1. Condensation polymerisation does not depend on
C=C bonds.

2. In condensation polymerisation, the monomers are
two different molecules. Each has two functional
groups (at both ends).

3. The two different monomers join at their
functional groups, by eliminating a small
molecule.

4. So, there are two products - a polymer and a
small molecule.

5. The small molecule removed is often water,
which is why the term condensation is used for
this type of polymerisation.

Example: functional groups

Example: functional groups

Example: functional groups

polymer water

Example 1: Making nylon

Properties of nylon:
■ can be drawn out into tough strong fibres that do not rot away

Uses to make:
■ thread
■ ropes
■ fishing nets
■ carpets

The reaction:

1. The two monomers used in making nylon are:
a. diamine (has -NH2 groups at both each ends)
b. dicarboxylic acid (has -COOH groups at both each end)

HO OH

diamine : OH
:
HO OH
HO
dicarboxylic acid

2. During the condensation reaction, the nitrogen atom at one end of
diamine has joined to the carbon atom at one end of dicarboxylic
acid, by eliminating a water molecule.

H2O is H2O
HO OH OH

3. The reaction continues at the other ends of the two monomers,
giving the polymer molecule nylon.

4. The group where the monomers joined is called the amide linkage.
So, nylon is called a polyamide.

Example 2: Making Terylene

Properties of Terylene:
■ can be drawn out into tough light, hard-wearing fibre that is easily

woven

Uses to make:
■ thread
■ fabric for shirts
■ bed linen

The reaction:

1. The two monomers used in making Terylene are:
a. dicarboxylic acid (has -COOH groups at both each end)
b. dialcohol (has -OH groups at both each end)

dicarboxylic acid :
dialcohol :

2. During the condensation reaction, the carbon atom at one end of
dicarboxylic acid has joined to the oxygen atom at one end of
dialcohol, by eliminating a water molecule.

3. The reaction continues at the other ends of the two monomers,
giving the polymer molecule Terylene.

4. The group where the monomers joined is called the ester linkage.
So, Terylene is called a polyester.

18.4
Making Use of Synthetic
Polymers

Learning objective:
■ Give at least five general properties of plastics.

Synthetic Polymers – Plastics:

1. All the materials we call plastics are
synthetic polymers, made by polymerisation
reactions in industry.

2. The starting compounds are very often
obtained from the refining of petroleum (e.g.
naphtha fraction of petroleum).

The Properties of Plastics:

▪ do not conduct electricity or heat
▪ unreactive – no affected by air, water, acids or other

chemicals

▪ light – low density
▪ strong – because their long chain molecules are

attracted to each other

▪ flexible – can be moulded
▪ waterproof
▪ not catch fire easily – but when you heat them, some

soften and melt, and some char (go black as if burned)

Changing the Properties:

1. The composition of plastic can be changed
to enhance its performance.

2. For example, we can use different
monomers or setup different reaction
conditions (e.g. temperature, pressure and
catalyst) to alter the properties of plastics.

Example 1: Poly(ethene)

Temperature : 50 oC Temperature : 200 oC
Pressure : 2000 atm
Pressure : 3 - 4 atm Additive : oxygen

The properties of plastics: The properties of plastics:
▪ The long chains of molecules are ▪ With a little oxygen present, the

packed close together. So, the chain will branch. The
plastic formed is dense. molecules can’t pack closely, so
the plastic is far less dense.

Example 2:

i. The strength of a plastics depends on the strength of the
intermolecular forces between the chains and how tangled the
chain becomes.

ii. The longer the chains the stronger they become. This is because
→ the longer the chains the more tangled they become.
→ the longer the chains the greater intermolecular forces.

18.5
Plastics: Here to Stay?

Learning objective:
■ Describe some of the environmental problems

caused by plastics.

Plastic Pollution:

1. Plastics are very useful materials, but they also pose
a big problem.

2. Plastics do not rot away.

3. They cannot be broken down by bacteria or other
natural organisms – they are non-biodegradable.

On the Land:

Plastic bags are
responsible for

much of the
litter seen
everywhere.

Plastic bottles the If burned, many
and other items problem plastics release

fill up landfill with toxic fumes
sites, when plastics together with
dumped in
household CO2.

rubbish.