Chapter 24 Addition polymers 24.1 Plastics as important materials in the modern world 24.2 What are plastics? 24.3 Addition polymerization 24.4 Properties and uses of some addition polymers 24.5 Thermal properties and structures of thermoplastics 24.6 Plastics and economy 24.7 Environmental issues related to the use of plastics Key terms Experiment 24.1 Check your progress Experiment 24.1 — Solution

The plastic age

Where do plastics come from? Petroleum (raw materials) Plastics fractional distillation manufacture Oil fractions (e.g. gas oil, fuel oil) alkenes cracking

WHY ARE PLASTICS SO USEFUL? Plastics have properties which make them very useful: Usually strong but light Inert: No reactions with air, water, acids, alkalis and most other chemicals 36.1 What are plastics?

Good insulators of heat and electricity Can be moulded easily into any shape 36.1 What are plastics?

Usually transparent Can be dyed 36.1 What are plastics?

Can be tailor-made to suit special requirements Usually flexible Can be tailor-made to suit special requirements 36.1 What are plastics?

Defining plastics Plastics are polymers which are made up of very large molecules. A polymer Polymerization monomer molecules large polymer molecule At some stage during processing, they can be turned into any desired shape by heating.  moulding

Wool Polymers and plastics All plastics are polymers. On the other hand, not all polymers are plastics. Wool is Polymer is not Plastic

What is addition polymerization? Addition polymerization is a reaction in which monomer molecules join together repeatedly to form polymer molecules, without the elimination of small molecules (such a H2O or HCl). The monomer molecules involved must contain carbon-carbon double bonds.

In most cases, the monomers can be represented by a general formula: where −X stands for an atom or a group of atoms such as −H, −CH3, , −Cl and so on.

By breaking open the carbon-carbon double bond, a monomer molecule will have two ‘free electrons’ which can join to other molecules: ‘free electrons’ that can join to other molecules

Each polymer chain consists of at least several hundred monomers joined together. A section of a polymer chain

Repeating unit A repeating unit is the group of atoms inside a polymer chain coming from a monomer (or set of monomers), which repeats to give the whole polymer structure.

The general equation for addition polymerization is: n molecules of monomer General formula to represent the polymer molecule (n usually varies from 1000 to 30 000)

Fig. 24. 4 A flexible paper-clip chain representing a polymer molecule Fig. 24.4 A flexible paper-clip chain representing a polymer molecule. Each clip represents a monomer molecule. Example 24.1 Class practice 24.3 Example 24.2

polyethene or polythene Polyethene [polythene] ethene polyethene or polythene

General properties: Low Density PE has a melting point of about 105°C. It softens in boiling water. It is flexible. High Density PE has a melting point of about 135°C. It is quite rigid.

Low-density polythene (straws) and high-density polythene (cup).

Some polyethene products

Toys made of low-density polyethene Example 24.3

Polypropene [polypropylene]

Properties: melting point: 165°C resistant to many chemical solvents, alkalis and acids.

Uses Some polypropene products

Polyvinyl chloride (polychloroethene) Polyvinyl chloride (PVC) is manufactured by heating chloroethene at about 60°C, in the presence of a catalyst (e.g. hydrogen peroxide H2O2). IUPAC name: chloroethene polychloroethene common name: vinyl chloride polyvinyl chloride

Properties: stiff brittle more flexible when mixed with a plasticiser properties can be varied by the addition of different amounts of plasticiser

Uses PVC pipes

Some PVC products Class practice 24.4

polystyrene or polyphenylethene Polystyrene is manufactured by heating styrene at about 100°C, in the presence of an organic peroxide as catalyst. styrene or phenylethene polystyrene or polyphenylethene

Fig. 24.10 Styrene is a colourless liquid.

Properties (Polystyrene): Properties (Expanded polystyrene): transparent hard brittle Properties (Expanded polystyrene): white solid foam very light quite rigid excellent heat insulator good shock-absorbent non-toxic

Some polystyrene products Uses Some polystyrene products

Foam cups and food boxes made of expanded polystyrene

polymethyl 2-methylpropenoate Perspex [Acrylic] Perspex is made by heating methyl 2-methylpropenoate at about 60°C, in the presence of an organic peroxide. methyl 2-methylpropenoate Perspex or polymethyl 2-methylpropenoate

Properties: highly transparent tough, but does not break easily but quite easily scratched

Uses This aquarium is made of Perspex

Do Question 22 on p. E56 Lenses of exterior lights of automobiles are made of Perspex Class practice 24.5 Activity 24.1 Activity 24.2

Thermoplastic and Thermoset A thermoplastic is a plastic which can be softened by heating and hardened by cooling, the process being repeatable any number of times. A thermoset is a plastic which once set hard cannot be softened by heating.

Do Question 15 on p. E59 weak intermolecular forces the weak intermolecular forces are overcome by heat or external force warm or pull Do Question 15 on p. E59 Experiment 24.1 Class practice 24.6

Poisonous plastic articles Problems associated with the use of plastics Problems Poisonous plastic articles E.g. PVC contains toxic substances Fire risk Burning of plastics produces harmful fumes.

Disposal of plastic waste Problems Disposal of plastic waste Non-biodegradable Burning plastic waste in incinerators would lead to air pollution. E.g. Burning PVC produces hydrogen chloride, chlorine gases, dioxins Activity 24.4 Activity 24.5

1. Reduce the use of plastics Solving plastic waste disposal problem 1. Reduce the use of plastics Fig. 24.19 Reducing use of plastic bags − Bring Your Own Bag (BYOB).

2. Reuse plastic articles Fig. 24.21 Many so-called ‘disposable’ plastic articles can in fact be used many times.

3. Recycle plastic waste Fig. 24.22 The international plastic coding system for recycling.

4. Make biodegradable plastics Do Question 19 on p. E64