Topic 6 - Polymers

INTRODUCING POLYMERS

• Polystyrene, nylon, terylene, PVC (polyvinyl chloride), formica, melamine and Teflon are all examples of synthetic polymers. 
• Plastics are materials which do not break down in normal use but which can be moulded by heat, pressure, or both.
• Most plastics are polymers, but not all polymers are plastics because sugars and starches can be classed as polymers.

ADDITION POLYMERS

• monomer= the starting molecule.
• Poly(ethene) - made by heating ethene under pressure with a catalyst. 
• Low density poly(ethene) is generally made from ethene at a pressure of about 1200 atmospheres and a temperature of 200°C in the presence of traces of oxygen - used for bags and wrappers. 
• High density poly(ethene) is made at lower temperatures and pressure (60°C and 1 atmosphere) in the presence of a catalyst - used for bottles and crates. 
• Poly(ethene) is cheap, waterproof, elastic and resistant to chemical attack. It melts at a low temperature and can easily be moulded and turned into a wide variety of products. It contains no free ions, so it is an excellent insulator – it does not conduct electricity at all. However like many synthetic polymers it is easily burnt, and this therefore restricts its use. It can also become a pollutant as discarded poly(ethene) resists attack…