9.4 Synthetic Polymers

Polymers are large molecules made up of many smaller and identical repeating units joined together by covalent bonds . These molecules are called monomers .Polymerisation is the chemical process by which the monomers are joined together to form a big molecule known as a polymer . A polymer is a macromolecules (a very big molecules) . Hence , the relative molecular mass of a polymer is large .The properties of a polymer are different from its monomers .

POLYMERS CAN DIVIDED INTO 2 TYPES:a) Naturally occurring polymers

Polymers that exists in living things in nature (plants and animals)

b) Synthetic polymerPolymers that are man-made by chemical processes in the laboratories.

NATURALLY OCCURRING POLYMERS

1) Naturally occurring polymers exist in plants or animals.

2) Examples of naturally occurring polymers are

a) Protein : in muscles,skin,silk,hair,wool and fur

b) Carbohydrates : in starch and cellulose.c) Natural rubber : in latex.3) Protein is formed by the polymerisation of

monomers known as amino acids. amino acids polymerisation protein

(monomers) (polymers)

4) Carbohydrates such as starch and cellulose consist of monomers known as glucose joined together chemically.

5) Natural rubber found in latex consist of monomers known as isoprene (2-methylbuta-1,3-diene) joined together chemically.

glucose polymerisation carbohydrates (monomers) (polymers)

H CH3 H H H CH3 H H n C = C - C = C - C – C = C – C -

H H H H n

isoprene(monomer) natural rubber (polymer)

SYNTHETIC POLYMERS1. Synthetic polymers are polymers made in the

industry from chemical substances.

2. Through scientific research , scientist are able to copy the structures of natural polymers to produce synthetic polymers.

3. Many of the raw materials for synthetic polymers are obtained from petroleum , after the refining and cracking processes.

4. The types of synthetic polymers include

a) Plastics

b) Fibre

c) Elastomers

PLASTIC

SYNTHETIC FIBRE

ELASTOMER1. An elastomer is a polymer that can regain its original

shape after being stretched or pressed.

2. Both natural rubber and synthetic rubber are examples of elastomers.

3. Examples of synthetic rubber are neoprene and styrene-butadiene rubber (SBR).

4. SBR is used to make car tyres.

5. There are two types of polymerisation processes: Addition polymerisation Condensation polymerisation

6. Plastics such as polythene and PVC are produced by addition polymerisation,whereas synthetic fibres such as nylon and Terylene are made by condensation polymerisation

CLASSIFICATION OF POLYMERS

CHARACTERISTICS OF POLYMERS

PROPERTIES OF POLYMERS

STRENGTH OF POLYMERS

APPLICATIONS OF POLYMERS

POLLUTION PROBLEM CAUSED BY SYNTHETIC POLYMERS

1. Most polymers are non-biodegradable,that is they cannot be decomposed by bacteria or other microorganisms. This will cause disposal problems as the polymers will not decay like other organic garbage.

2. Dicarded plastic items may cause blockage of drainage systems and rivers thus causing flash floods.

3. Plastic bottles and containers that are not buried in the ground will become breeding grounds for mosquitoes which will cause diseases such as dengue.

4. Small plastic items that are thrown into the rivers,lakes and seas are sometimes swallowed by aquatic animals. These animals may die from choking.

5. The open burning of polymers may release harmful and poisonous gases that will cause air pollution. For example,the burning of PVC will release hydrogen chloride gas which contributes to the acid rain problem. The burning of some polymers will release toxic gas such as hydrogen cyanide.

6. The main source of raw materials for the making of synthetic polymers is petroleum. Petroleum is a non-renewable resource.

METHODS TO OVERCOME ENVIRONMENTAL PROBLEMS OF

POLYMERS REDUCE,REUSE AND RECYCLE SYNTHETIC

POLYMERS1. Reduce the use of non-biodegradable

polymers.2. Polymers are collected and reused or

reprocessed to make new items. The biggest problem is the collection and separation. Not only must the plastic be separated form other types of solid waste but the different type of polymers must be separated from each other.

DEVELOP BIODEGRADABLE POLYMERS The polymers can be decomposed by

bacteria,other microorganisms or simply by sunlight (photodegradable). One type of biodegradable polymer was developed by incorporating starch molecules into the plastic materials so that they can be decomposed by bacteria. However, biodegradable polymers are usually more expensive.