Addition polymerization
From Wikipedia, the free encyclopedia
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:
- 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.
- chain propagation
- 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
- 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.
[edit] 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.ja:付加重合
