- Addition polymer
An addition polymer is a polymer which is formed by an
addition reaction , where manymonomer s bond together via rearrangement of bonds without the loss of any atom or molecule. This is in contrast to acondensation polymer which is formed by a condensation reaction where a molecule, usually water, is lost during the formation.Contrast with condensation polymers
With exception of
combustion , the backbone of addition polymers are generally chemicallyinert . This is due to the very strong C-C and C-H bonds and lack of polarisation within many addition polymers. For this reason they are non-biodegradable and hard to recycle. This is, again, in contrast to condensation polymers which are bio-degradable and can be recycled.Many exceptions to this rule are products of
ring-opening polymerization , which tends to produce condensation-like polymers even though it is an additive process. For example, poly [ethylene oxide] is chemically identical topolyethylene glycol except that it is formed by openingethylene oxide rings rather than eliminating water fromethylene glycol .Nylon 6 was developed to thwart thepatent on nylon 6,6, and while it does have a slightly different structure, its mechanical properties are remarkably similar to its condensation counterpart.One universal distinction between polymerization types is development of molecular weight by the different modes of propagation. Addition polymers form high molecular weight chains rapidly, with much monomer remaining. Since addition polymerization has rapidly growing chains and free monomer as its reactants, and condensation polymerization occurs in step-wise fashion between monomers, dimers, and other smaller growing chains, the effect of a polymer molecule's current size on a continuing reaction is profoundly different in these two cases. This has important effects on the distribution of molecular weights, or
polydispersity , in the finished polymer.History
The first useful addition polymer was made by accident in 1933 by ICI chemists
Reginald Gibson andEric Fawcett . They were carrying out a series of experiments which involved reacting organic compounds under high temperatures and high pressures. They set up an experiment to react ethene with benzaldehyde in the hope of producing aketone . They left the reaction vessel overnight, and the next morning they found a small amount of a white waxy solid. It was shown later that this solid was polyethene.Usage
Addition polymers are widely used today in the form of rubber.This includes
polyethene (polythene),polypropylene ,polystyrene , and PVC.
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