Chain-growth 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.

The main characteristics are:

• polymerization process takes place in three distinct steps:
  • chain initiation
  • chain propagation
  • chain termination
• no small molecules are eliminated in this process like in condensation polymerization.
• new monomer adds on the growing polymer chain via the reactive active centre
• High molecular weight polymer is formed at low conversion (in contrast to condensation polymerization, also known as step-growth polymerization
• The active centre 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
• a monomer molecule can be a
  • unsaturated compound like ethylene or acetylene which make them reactive.
  • Alicyclic compound see ring-opening polymerization
• require an initiator to start the chemical process. Typical initiators include any organic compound with a labile group: e.g. azo (-N=N-), disulfiđde (-S-S-), or peroxide (-O-O-). Two examples are benzoyl peroxide and AIBN.
• Given special reactants and reaction conditions an addition polymerization can be considered a living polymerization.

Random 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.