https://doi.org/10.1351/goldbook.C00958
A
chain reaction
in which the growth of a polymer chain
proceeds exclusively by reaction(s) between monomer(s)
and reactive site(s) on the polymer chain with regeneration of the reactive site(s) at the end of each growth step.Notes:
- A chain polymerizationconsists ofinitiationandpropagationreactions, and may also includeterminationandchain transferreactions.
- The adjective 'chain' in 'chain polymerization' denotes a 'chain reaction' rather than a 'polymer chain'.
- Propagationin chainpolymerizationusually occurs without the formation of small molecules. However, cases exist where a low-molar-mass by-product is formed, as in thepolymerizationof oxazolidine-2,5-diones derived from amino acids (commonly termed amino-acid N-carboxyanhydrides). When a low-molar-mass by-product is formed, the adjective 'condensative' is recommended to give the term condensative chain polymerization
- The growth steps are expressed by:
where denotes the growing chain ofdegree of polymerization , amonomer(s)and a low-molar-mass by-product formed in the case of condensative chain polymerization. - The term 'chain polymerization' may be qualified further, if necessary, to specify the type of chemical reactions involved in the growth step, e.g. ring-opening chainpolymerization, cationic chainpolymerization.
- There exist, exceptionally, some polymerizations that proceed via chain reactions that, according to the definition, are not chain polymerizations. For example, the polymerization:proceeds via a radicalchain reactionwithintermoleculartransfer of the radical centre. The growth step, however, involves reactions between molecules of all degrees ofpolymerizationand, hence, thepolymerizationis classified as apolyaddition. If required, the classification can be made more precise and thepolymerizationdescribed as a chain-reactionpolyaddition.