Term: chain polymerization
https://doi.org/10.1351/goldbook.C00958

Definition:
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:
0) A chain @P04740@ consists of @I03042@ and @P04881-1@ reactions, and may also include @T06274@ and @C00963@ reactions.
1) The adjective 'chain' in 'chain @P04740@' denotes a '@C00960@' rather than a 'polymer chain'.
2) @P04881-2@ in chain @P04740@ usually occurs without the formation of small molecules. However, cases exist where a low-molar-mass by-product is formed, as in the @P04740@ of oxazolidine-2,5-diones derived from amino acids (commonly termed amino-acid N-carboxy @A00354@). When a low-molar-mass by-product is formed, the adjective 'condensative' is recommended to give the term condensative chain polymerization
3) The growth steps are expressed by: \[\text{P}_{x} + \text{M}\rightarrow \text{P}_{x + 1}\hspace{5pt}(+\ \text{L}) \hspace{35pt} \{x\}\in \{1,2,\ \dots \infty\};\] where Px denotes the growing chain of @D01569@ x, M a @M04017@ and L a low-molar-mass by-product formed in the case of condensative chain polymerization.
4) The term 'chain @P04740@' may be qualified further, if necessary, to specify the type of chemical reactions involved in the growth step, e.g. ring-opening chain @P04740@, cationic chain @P04740@.
5) There exist, exceptionally, some polymerizations that proceed via chain reactions that, according to the definition, are not chain polymerizations. For example, the @P04740@: C00958.png proceeds via a radical @C00960@ with @I03098@ transfer of the radical centre. The growth step, however, involves reactions between molecules of all degrees of @P04740@ and, hence, the @P04740@ is classified as a @P04720@. If required, the classification can be made more precise and the @P04740@ described as a chain-reaction @P04720@.

Related Terms:
1) polymerization (http://doi.org/10.1351/goldbook.P04740).
2) initiation (http://doi.org/10.1351/goldbook.I03042).
3) propagation (http://doi.org/10.1351/goldbook.P04881-1).
4) termination (http://doi.org/10.1351/goldbook.T06274).
5) chain reaction (http://doi.org/10.1351/goldbook.C00960).
6) propagation (http://doi.org/10.1351/goldbook.P04881-2).
7) anhydrides (http://doi.org/10.1351/goldbook.A00354).
8) degree of polymerization (http://doi.org/10.1351/goldbook.D01569).
9) monomer(s) (<em>in polymers</em>) (http://doi.org/10.1351/goldbook.M04017).
10) intermolecular (http://doi.org/10.1351/goldbook.I03098).
11) polyaddition (http://doi.org/10.1351/goldbook.P04720).
12) chain transfer (http://doi.org/10.1351/goldbook.C00963).
13) chain (<em>in polymers</em>) (http://doi.org/10.1351/goldbook.C00946).

Image: Polymerization Reaction (https://goldbook.iupac.org/img/inline/C00958.png) 

Source: PAC, 1996, 68, 2287. 'Glossary of basic terms in polymer science (IUPAC Recommendations 1996)' on page 2306 (https://doi.org/10.1351/pac199668122287)

Citation: 'chain polymerization' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C00958

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