The basic units of the long chain polymers are called monomers, which join, by two polymerization processes for producing resins known as addition and condensation reactions. Addition PolymerizationThe monomers contain at least one double bond between a pair of carbon atoms. During this process, unsaturated or cyclic molecules add together without elimination of a portion of the monomer molecule. This form of polymerization produces only specific polymer chain lengths, and a repeating unit derived from simple organic molecules (monomers) is apparently common throughout the chain. (Matthew, 2001)The average molecular weights for the addition polymers are generally by comparison larger than those of condensation polymers. For example, polymers involving the addition reactions include: Polyethylene (PE), commonly produced by the cracking of ethane gas, forms the basis for the largest single class of plastics, the polyethylenes. Ethylene monomer has the chemical composition; CH2=CH2. Branched versions are known as low-density polyethylene (LDPE) or linear
low-density polyethylene (LLDPE); the linear versions are known as high-density
polyethylene (HDPE) and ultrahigh molecular weight polyethylene (UHMWPE).
The overall chemical reaction: catalystnCH2 = CH2 CH2 CH2 CH2 CH2
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