The joining of two or more simple molecules or monomers, to form a new compound, a polymer which has the same empirical formula.
             Mechanism of the Polymerisation of Ethene
             Thousands of ethene molecules join up to form a type of poly(ethene) known as low density polythene.
             [CH2=CH2]n [ CH2-CH2 ]n number of joining molecules can vary from 200-2000
             The mechanism is known as a free radical reaction as it is the radicals which initiate the three stage process of polymerisation.
             Stage 1: Initiation by free radicals
             R l + H2C=CH2 R CH2 CH2 l where r is the radical
             Each time a radical hits an ethene molecule a new, longer radical is formed.
             R CH2 CH2 l + H2C=CH2 R CH2 CH2 CH2 CH2 l
             R H2 CH2 CH2 CH2 l + H2C=CH2 R CH2 CH2 CH2 CH2 CH2 CH2 l
             Eventually two radicals combine and the process stops as no new radicals are formed (1)
             As the chains grow by radical mechanism, it is possible for a radial exchange to occur to give a radical within the chain (2)
             By this mechanism the chains can become more branched, the higher the temperature and pressure the greater the degree of branching. It is difficult for the branched chains to fit closely together, hence the name low density poly(ethene).
             There are two types Hdpe and ldpe with different structures and properties:
             Branched nature makes it difficult for chains to come together. As a result intermolecular forces are much weaker than the would be in a packed structure.
             Low softening temperature (can be melted by boiling water)
             Suitable only for a limited range of applications
             This can be produced by combining ethene with various metal compounds like trimethylaluminium.
             Al (CH2)2 C2H5 + H2C=CH2
             The chains are able...