Terms for Mechanisms of Polymer Growth

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The Subcommittee on Polymer Terminology (SPT, Division IV) has recently published a paper in Polymer Chemistry (https:// doi.org/10.1039/d2py00086e) outlining their concerns with terms describing basic classification of mechanisms of polymer growth. The terms “step-growth” and “chain-growth,” and a variety of related terms, are used widely by the polymer community. In brief, “step-growth” typically refers to polymers that are synthesized from one (or more) type(s) of multifunctional monomer(s) where at least bifunctionality is required, with growth occurring between monomers, oligomers, or polymers of any length. An example is the synthesis of linear polyamides from diamines and dicarboxylic acids. “Chain-growth” generally describes polymers that increase in molar mass by a chain reaction process of monomers adding to polymeric active sites, which are typically created through inclusion of an external initiator in the polymerization reaction. An example is the synthesis of polystyrene from styrene and a radical initiator.

IUPAC has never endorsed the terms “step-growth” and “chain-growth,” in part because they do not clearly distinguish between these two mechanisms of polymer growth—all polymers grow in a series of steps to form polymer chains. SPT therefore recommended four terms in 1994: These included polyaddition and polycondensation for polymers that grow in a “step-growth” mechanism, and chain polymerization and condensative chain polymerization for polymers that grow following a “chain-growth” mechanism. An analysis of various textbooks in general chemistry, organic chemistry, and polymer chemistry and related field revealed that these recommended terms have not been taken up by the polymer community. In fact, there is no consensus among textbook authors to distinguish between these two fundamentally different mechanisms of polymer growth. The paper details several reasons for why this may be the case, including the lack of generic, umbrella terms covering the condensative and non-condensative versions of the mechanisms of polymer growth.

The paper also details a short history of various terms used, revealing the circuitous path that led to the position we are in today, where “step-growth” and “chain-growth” persist alongside the related terms polyaddition, which is different from the deprecated term “addition polymerization,” and polycondensation, which is different from the deprecated term “condensation polymerization.” This lack of clear and consistent terminology leads to confusion among practitioners of polymer science and students learning polymer science, as well as difficulties in translating these terms to other languages.

https://iupac.org/project/2019-027-1-400

This paper does not recommend new terms. Instead, the members of SPT working on this project seek suggestions from the community on how to provide clear, simple, and consistent terms to describe the two major mechanisms of polymer growth and their subclasses. They ask that ideas, concerns, and suggestions be sent to polymer.terminology@iupac.org.

For more information and comments, contact Task Group Chair John B. Matson <jbmatson@vt.edu> https://iupac.org/project/2019-027-1-400

CITE: "Terms for Mechanisms of Polymer Growth" Chemistry International, vol. 44, no. 3, 2022, pp. 30-30. https://doi.org/10.1515/ci-2022-0316