THE POLYMER INDUSTRY (1)

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Polyvinyl chloride Other addition polymers Additional questions	The petroleum industry The chloralkali and Solvay processes The polymer industry (2) The fertiliser industry Ammonia - Nitric acid - Sulphuric acid Electrochemical cells	Data Glossary
Learning Outcomes
After studying this section, you will be familiar with (a) the chemical principles underlying the manufacture of polyvinyl chloride and (b) the composition of some other commonly-used addition polymers.

Polyvinyl chloride:

Polyvinyl chloride is a polymer that has found widespread use in the building industry. It is commonly used for the manufacture of gutters and down pipes (above, left), plumbing (above, center), and conduit piping for electrical installations (above, right). It is also used to make credit cards, electrical cable insulation, upholstery and waterproof clothing.

PVC is a hard and relatively brittle THERMOPLASTIC material, which means that it softens on heating. THERMOSETTING polymers, on the other hand, do not soften on heating. In order to make PVC more pliable, for uses such as motor car upholstery and waterproof clothing, certain substances called PLASTICISERS are added during the final manufacturing process.

The manufacture of PVC starts off with ethylene (a by-product of petroleum cracking) and chlorine (obtained from the chloralkali process). These two gases react in the presence of the catalyst iron(III) chloride, FeCl₃, producing 1,2-dichloroethane (ethylene dichloride). When this substance is heated to 500 ºC at 1.5-3.0 MPa, it loses hydrogen chloride by an elimination reaction, to form vinyl chloride monomer, CH₂=CHCl:

Vinyl chloride is polymerised to form polyvinyl chloride. Note that this is an ADDITION POLYMERISATION.

The hydrogen chloride that is formed in the reaction that produces vinyl chloride is not allowed to go to waste! After all, it represents half the chlorine invested in the overall process. In the chemical industry, every effort is made to recycle unwanted products of reactions. In this case, the hydrogen chloride is reacted with oxygen (from the air) and ethylene in the presence of copper(II) chloride, CuCl₂, to form 1,2-dichloroethane. In this way, the net production of HCl is zero, and chlorine is not wasted:

Concern has been voiced about the possible toxicity of PVC, which may at times contain small quantities of the toxic monomer, as well as the possible toxicity of plasticiser that are used. For this reason, the use of PVC in the food industry (for wrapping, for example) is banned in certain countries. The stability of PVC also means that it survives in the environment for a very long time.

Other addition polymers:

Addition polymers of various types find numerous applications in industry and the home. They are produced by polymerising a MONOMER until molecules of a certain size, the POLYMER, are obtained. These molecules make up materials with diverse useful properties, illustrated in the table below.

Additional questions