Polymers

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[link] summarises the formulae, properties and uses of some of the most common plastics.

A summary of the formulae, properties and uses of some common plastics

Name	Formula	Monomer	Properties	Uses
Polyethene (low density)	-(CH $_{2}$ -CH $_{2}$ ) $_{n}$ -	CH $_{2}$ =CH $_{2}$	soft, waxy solid	film wrap and plastic bags
Polyethene (high density)	-(CH $_{2}$ -CH $_{2}$ ) $_{n}$ -	CH $_{2}$ =CH $_{2}$	rigid	electrical insulation, bottles and toys
Polypropene	-[CH $_{2}$ -CH(CH $_{3}$ )] $_{n}$ -	CH $_{2}$ =CHCH $_{3}$	different grades: some are soft and others hard	carpets and upholstery
Polyvinylchloride (PVC)	-(CH $_{2}$ -CHCl) $_{n}$ -	CH $_{2}$ =CHCl	strong, rigid	pipes, flooring
Polystyrene	-[CH $_{2}$ -CH(C $_{6}$ H $_{5}$ )] $_{n}$	CH $_{2}$ =CHC $_{6}$ H $_{5}$	hard, rigid	toys, packaging
Polytetrafluoroethylene	-(CF $_{2}$ -CF $_{2}$ ) $_{n}$ -	CF $_{2}$ =CF $_{2}$	resistant, smooth, solid	non-stick surfaces, electrical insulation

Plastics

It is possible for macromolecules to be composed of more than one type of repeating monomer. The resulting polymer is called a copolymer . Varying the monomers that combine to form a polymer, is one way of controlling the properties of the resulting material. Refer to the table below which shows a number of different copolymers of rubber, and answer the questions that follow:

Monomer A	Monomer B	Copolymer	Uses
H $_{2}$ C=CHCl	H $_{2}$ C=CCl $_{2}$	Saran	films and fibres
H $_{2}$ C=CHC $_{6}$ H $_{5}$	H $_{2}$ C=C-CH=CH $_{2}$	SBR (styrene butadiene rubber)	tyres
H $_{2}$ C=CHCN	H $_{2}$ C=C-CH=CH $_{2}$	Nitrile rubber	adhesives and hoses
H $_{2}$ C=C(CH $_{3}$ ) $_{2}$	H $_{2}$ C=C-CH=CH $_{2}$	Butyl rubber	inner tubes
F $_{2}$ C=CF(CF $_{3}$ )	H $_{2}$ C=CHF	Viton	gaskets

Give the structural formula for each of the monomers of nitrile rubber.
Give the structural formula of the copolymer viton.
In what ways would you expect the properties of SBR to be different from nitrile rubber?
Suggest a reason why the properties of these polymers are different.

In your home, find as many examples of different types of plastics that you can. Bring them to school and show them to your group. Together, use your examples to complete the following table:

Object Type of plastic Properties Uses

Thermoplastics and thermosetting plastics

A thermoplastic is a plastic that can be melted to a liquid when it is heated and freezes to a brittle, glassy state when it is cooled enough. These properties of thermoplastics are mostly due to the fact that the forces between chains are weak. This also means that these plastics can be easily stretched or moulded into any shape. Examples of thermoplastics include nylon, polystyrene, polyethylene, polypropylene and PVC. Thermoplastics are more easily recyclable than some other plastics.

Thermosetting plastics differ from thermoplastics because once they have been formed, they cannot be remelted or remoulded. Examples include bakelite, vulcanised rubber, melanine (used to make furniture), and many glues. Thermosetting plastics are generally stronger than thermoplastics and are better suited to being used in situations where there are high temperatures. They are not able to be recycled. Thermosetting plastics have strong covalent bonds between chains and this makes them very strong.

Case study : biodegradable plastics

Read the article below and then answer the questions that follow.

Our whole world seems to be wrapped in plastic. Almost every product we buy, most of the food we eat and many of the liquids we drink come encased in plastic. Plastic packaging provides excellent protection for the product, it is cheap to manufacture and seems to last forever. Lasting forever, however, is proving to be a major environmental problem. Another problem is that traditional plastics are manufactured from non-renewable resources - oil, coal and natural gas. In an effort to overcome these problems, researchers and engineers have been trying to develop biodegradable plastics that are made from renewable resources, such as plants.

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Source: OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2

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Object	Type of plastic	Properties	Uses