The term “step-growth polymerization” remains in widespread use despite a 1994 document from the Subcommittee on Polymer Terminology deprecating it because all polymerizations are a series of steps. The term “chain-growth polymerization” was also deprecated at this time, but it is still also widely used. The lack of adherence to IUPAC terms suggested in the 1994 document is likely because no alternative to “step-growth” was suggested. The term “non-chain polymerization” now appears in documents of the Subcommittee on Polymer Terminology, but this is a poor term because it defines something based on what it is not. This project aims to update the 1994 BASIC CLASSIFICATION AND DEFINITIONS OF POLYMERIZATION REACTIONS* document to address these concerns in the context of existing trends in polymer synthesis.
*Pure Appl. Chem., 1994, 66, 2483-2486; https://doi.org/10.1351/pac199466122483
The project encompasses several issues related to basic terminology in polymer synthesis:
There exist several dilemmas with current IUPAC terminology and current usage of terms in the polymer community:
1. The 1994 document seeks a clear distinction in terminology between the chain or non-chain nature of the growth reaction, but use of the term ‘non-chain’ for non-chain polymerizations where reactions can take place between chains of any degree of polymerization has not taken off. Furthermore, the term ‘non-chain’, while comprehensive, privileges the chain polymerization point of view and it would be better to have a more neutral term. In short, there is no IUPAC-approved term for “step-growth polymerization.”
2. “Step-growth polymerization” was deprecated because both chain and non-chain polymerizations require steps of some kind. The 1994 document clearly points out that both have steps.
3. The term “step-growth” creates problems in languages where it is translated as “stair-growth”, which is even more confusing than the English term.
4. The terms introduced in the 1994 document, polyaddition and polycondensation (the two types of “step-growth polymerization”), call to mind addition polymerization (i.e., chain polymerization) and condensation polymerization (i.e., step-growth polymerization).
5. The term “chain polymerization” creates confusion between “chain reaction” and “polymer chain”.
6. No polymerization terms were provided for polymers that are made one unit at a time, such as in peptide synthesis, DNA synthesis, single-unit monomer insertion sequences, or other sequence-defined polymers. While these types of compounds are clearly polymers, there is no term describing the iterative process used to make them.
7. ‘Polycondensation’ and ‘polyaddition’ do not exhaust the possibilities of non-chain polymerizations, in that polymerization via biradicals (e. g., Gilch polymerization, Macromolecules, 2017, 50(13), 4952–4961; DOI) may proceed to a large degree by reactions between molecules of any degree of polymerization in which bonds are formed by radical combination [‘colligation’, according to PAC 66(5), 1077-1184, 1994; https://doi.org/10.1351/pac199466051077].
1. We will publish a “dilemma document” in Polym. Chem., an RSC publication read widely by polymer chemists, outlining these problems to the polymer community. In this paper we will discuss historical terms for polymerization methods, the deprecation of step-growth in 1994 by IUPAC, the problems with various terms in languages other than English, include a survey of current terms used in textbooks, discuss the question of whether making a polymer one unit at a time is indeed a “polymerization”, and propose possible solutions to these terminological dilemmas. Possible solutions include making an effort to enforce current IUPAC terminology, reintroducing step-growth and chain-growth despite their issues, or coming up with new terms. We will ask for readers to send responses to Polym. Chem., which the journal has agreed to collect into a Reply article.
2. Based on responses to our dilemma document, we will consider whether a new term is needed to capture both polycondensation and polyaddition, in other words, an umbrella term to replace “step-growth” polymerization.
3. In addition to replacing step-growth and chain-growth, it may be necessary to introduce a new term which includes everything where the stoichiometric conditions [1994, note 1.4] are met but where the reaction does not proceed by a series of steps that would be recognized as a chain reaction in non-polymerization contexts (e.g., single unit monomer insertion, solid-supported peptide synthesis). We need to determine whether something that is clearly a polymer (i.e., a peptide) can be made without a polymerization reaction, or whether a new term is needed to describe these polymerizations.
4. To further support our efforts, we will consult informally with prominent polymer scientists, both with and without IUPAC experience, in academia and industry, working on a variety of polymerization methodologies.
Project announcement published in Chem Int Jan 2020, p. 29
Page last update 12 Feb 2020