1. 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

2. The plastic age

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

4. 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?

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

6. Usually transparent
Can be dyed
36.1 What are plastics?

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

8. 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

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

10. 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.

11. 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.

12. 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

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

14. 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.

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

16. Fig. 24. 4 A flexible paper-clip chain representing a polymer molecule
Fig 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

17. polyethene or polythene
Polyethene [polythene]
ethene
polyethene or polythene

18. 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.

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

20. Some polyethene products

21. Toys made of low-density polyethene
Example 24.3

22. Polypropene [polypropylene]

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

24. Uses
Some polypropene products

25. 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

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

27. Uses
PVC pipes

28. Some PVC products
Class practice 24.4

29. 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

30. Fig. 24.10 Styrene is a colourless liquid.

31. 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

32. Some polystyrene products
Uses
Some polystyrene products

33. Foam cups and food boxes made of expanded polystyrene

34. 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

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

36. Uses
This aquarium is made of Perspex

37. 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

38. 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.

39. 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

40. 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.

41. 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

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

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

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

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