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 polymerization consists of initiation and propagation reactions, and may also include termination and chain transfer reactions.
- The adjective 'chain' in 'chain polymerization' denotes a 'chain reaction' rather than a 'polymer chain'.
- Propagation in chain polymerization usually occurs without the formation of small molecules. However, cases exist where a low-molar-mass by-product is formed, as in the polymerization of oxazolidine-2,5-diones derived from amino acids (commonly termed amino-acid N-carboxy anhydrides). 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: \[\rm{P}_{x} + \rm{M}\rightarrow \rm{P}_{x + 1}\hspace{5pt}(+\ \rm{L}) \hspace{35pt} \{x\}\in \{1,2,\ \dots \infty\};\] where \(P_{x}\) denotes the growing chain of degree of polymerization \(x\), \(M\) a monomer and \(L\) 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 chain polymerization, cationic chain polymerization.
- 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 radical chain reaction with intermolecular transfer of the radical centre. The growth step, however, involves reactions between molecules of all degrees of polymerization and, hence, the polymerization is classified as a polyaddition. If required, the classification can be made more precise and the polymerization described as a chain-reaction polyaddition.
