Addition polymerization

} Addition polymerization,also called polyaddition or chain growth polymerization, is a polymerization technique where monomer molecules add on to a growing polymer chain one at a time.
 * nM (monomer) --> -(-M-)n- (polymer)

The main characteristics are:


 * polymerization process takes place in three distinct steps:
 * 1) chain initiation, usually by means of an initiator which starts the chemical process.  Typical initiators include any organic compound with a labile group: e.g. azo (-N=N-), disulphide (-S-S-), or peroxide (-O-O-).  Two examples are benzoyl peroxide and AIBN.
 * 2) chain propagation
 * 3) chain termination, which occurs either by combination or disproportionation. Termination, in radical polymerization, is when the free radicals combine and is the end of the polymerisation process.
 * some side reactions may occur, such as: chain transfer to monomer, chain transfer to solvent, and chain transfer to polymer.


 * unlike condensation polymerization (also known as step-growth polymerization):
 * high molecular weight polymer is formed at low conversion
 * no small molecules are eliminated in this process
 * new monomer adds on the growing polymer chain via the reactive active centre which can be a
 * free radical in free radical addition polymerization
 * carbocation in cationic addition polymerization
 * carbanion in anionic addition polymerization
 * organometallic complex in coordination polymerization
 * the monomer molecule can be a
 * unsaturated compound like ethylene or acetylene which make them reactive.
 * Alicyclic compound see ring-opening polymerization
 * given special reactants and reaction conditions an addition polymerization can be considered a living polymerization.
 * above a certain ceiling temperature, no polymerization occurs.

Some Examples

 * benzoyl peroxide is an initiator for the free radical addition polymerization of styrene to produce polystyrene.
 * Aluminium chloride is an initiator for the cationic addition polymerization of isobutylene to form isobutyl synthetic rubber.

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