Addition polymerization

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Addition polymerisation, also called polyaddition or chain growth polymerization, is a polymerisation technique where unsaturated monomer molecules add on to a growing polymer chain one at a time [1]. It can be represented with the chemical equation:

where n is the degree of polymerization.


The main characteristics are:

  • polymerisation 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-), disulfide (-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 polymerisation, 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.



  1. Introduction to Polymers 1987 R.J. Young Chapman & Hall ISBN 0-412-22170-5