Polymer Chemistry Blog

An international group of polymer scientists from the International Union of Pure and Applied Chemistry (IUPAC) Subcommittee on Polymer Terminology (SPT) convey concerns with the basic terms typically used for classifying methods of polymer synthesis and initiate a dialogue with the broader polymer community to resolve terminology shortcomings.

In 1994 the IUPAC SPT highlighted long-standing problems with the widely used terms “step-growth polymerization” and “chain-growth polymerization,” which describe two discrete mechanisms of polymer growth, and depreciated their use since they do not describe the fundamental differences in the growth of polymers by these methods and are often confusing. To address this, the 1994 SPT members recommended the terms polycondensation and polyaddition for the two variants of “step-growth polymerization”, and similarly chain polymerization and condensative chain polymerization for the two variants of “chain-growth polymerization”. However, these terms have not been widely adopted by the community, and have also created confusion.

In this contribution, current IUPAC SPT members provide detailed descriptions of these two processes and outline concerns associated with the terms “step-growth,” “chain-growth,” and related terms. By discussing in detail the historical development of these terms and analyzing their use in current textbooks, the authors underline the lack of consensus in the terminology used within the polymer community. Interestingly, they demonstrate how the similarity of these terms leads to further confusion when translating into languages other than English. Finally, examples of polymerizations that cannot be classified under the umbrella of the existing definitions and have no designated terminology are discussed.

In 2019, IUPAC recognized the need to resolve these polymer terminology shortcomings and approved a project aimed to propose new terminologies. The authors, as members of the IUPAC SPT task group studying this issue, aim to clarify the naming of polymerisation processes and invite all members of the community to contribute by emailing to polymer.terminology@iupac.org.

Tips/comments directly from the authors:

• We, the subcommittee of polymer nomenclature (SPT), want to raise attention to a long-standing dilemma in the terms that many of us use every day: “step-growth” and “chain-growth” polymerization.
• A number of terms have been used over the past century to describe these two fundamental mechanisms of polymer growth, and many prominent polymer chemists have noted their shortcomings in textbooks.
• We detail here the history of the terms, current usage in textbooks, and our specific concerns.
• In particular, we invite feedback from the broader polymer community, including from students, lecturers, researchers, and anyone who uses polymer science regularly.

Reconsidering terms for mechanisms of polymer growth: the “step-growth” and “chain-growth” dilemma, Polym. Chem., 2022, 13, 2262-2270.

Link to the paper: https://pubs.rsc.org/en/content/articlelanding/2022/py/d2py00086e

You can follow the authors on twitter: @IUPACPolymer

Dr. Kelly Velonia is an Advisory Board Member and a Web Writer for Polymer Chemistry. She joined the Department of Materials Science and Technology in 2007. Research in her group focuses on the synthesis and applications of bioconjugates and biopolymers.

Lehnen et al. highlight the role of reversible deactivation as a key difference between photo-iniferter and conventional RAFT polymerization.

The use of light has become increasingly widespread in diverse polymerization approaches including reversible-addition fragmentation chain-transfer (RAFT) strategies. Among these, the photo-iniferter (PI)-RAFT polymerization in which light directly activates the chain transfer agent (CTA), has been shown to overcome several of the restrictions of conventional RAFT resulting in increased chain end fidelity. In this context, reversible deactivation is accepted to determine the fate of the growing radical via pathways that need to be understood to offer the means to further push the limits of PI-RAFT polymerization.  

To address this, Hartlieb and collaborators studied the PI-RAFT using an acrylamide (N-acryloyl morpholine) and a xanthate ((2-((ethoxycarbonothioyl)thio)propionic acid)). This monomer-CTA pair combination was selected on the basis of the low chain transfer capabilities (C_tr < 1) expected to result in high dispersities (>1.5). When targeting different degrees of polymerization (DP), the control over the molecular weight distribution was not found to significantly increase. However, control could be achieved through slow monomer addition that results in increasing the numbers of activation-deactivation events per monomer addition. Importantly, the high livingness associated with PI-RAFT proved to be invaluable in chain extension experiments since it was found to enable the straightforward, easy and rapid synthesis of very high molecular weight multiblock copolymers with up to 20 blocks and a high number of repeating units per block (DP = 25-100) with impressive precision.  

In summary this study highlights the role of reversible deactivation and employs the high livingness of PI-RAFT to demonstrate its enormous potential for the synthesis of polymeric materials and more specifically segmented macromolecules.

Tips/comments directly from the authors:

• We want to emphasize how fast and easy polymerization reactions can be performed using this technique as the shown xanthate is an extremely powerful iniferter
• The shown multiblocks were produced in a very straight forward way; no rigorously clean or inert conditions or specialized equipment.
• The photo-iniferter process is older than RAFT polymerization but its full potential isn’t used yet.  

The difference between photo-iniferter and conventional RAFT polymerization: high livingness enables the straightforward synthesis of multiblock copolymers, Polym. Chem., 2022, 13, 1537-1546

Link to the paper: https://pubs.rsc.org/en/content/articlelanding/2022/py/d1py01530c

Link to Dr Matthias Hartlieb’s group website: https://www.uni-potsdam.de/polybio

You can follow Dr Matthias Hartlieb on Twitter: @PolyBioPotsdam. 

Dr. Kelly Velonia is an Advisory Board Member and a Web Writer for Polymer Chemistry. She joined the Department of Materials Science and Technology in 2007. Research in her group focuses on the synthesis and applications of bioconjugates and biopolymers.

Guan et al. develop iron-containing poly(ionic liquid) (Fe-PIL) membranes with anti-fouling properties enhanced by a heterogeneous Fenton reaction.

The life span of membranes used in various separation technologies is often limited by fouling causing decreased performance and large economic costs. Recently, poly(ionic liquid)s (PILs) have been employed to prepare membranes with a large range of applications due to their unique material properties including excellent stability, processability and flexibility. Although PIL membranes are less prone to fouling and easier to clean due to their charged nature, the problem of irreversible pollutant deposition can limit their efficiency.  

To address this, Zhang and collaborators developed iron-containing PIL (Fe-PIL) membranes and used them as catalysts for heterogenous Fenton reaction. Poly(4-vinylpyridine)-b-polysulfone-b-poly(4-vinylpyridine) (PSF-b-P4VP) blend membranes were synthesized via Cu(0)-RDRP. The pore size and hydrophilicity of the membranes fabricated via NIPS, were found to depend on the block ratio of the polymer. A quaternization reaction followed by coordination with Fe(II) bromide was employed to generate the Fe-PILs on the surface of the polysulfone blends.  The membranes were shown to possess low surface roughness, increased hydrophilicity, anti-fouling properties and scalability. The dispersibility of the catalyst and the catalytic efficiency in heterogeneous Fenton reactions were shown to be excellent in a broad pH range from acidic to neutral and basic conditions. More importantly, the Fe-PIL membranes exhibited superior synergistic performance with filtration in the dynamic heterogeneous Fenton reaction and excellent reusability as they could be maintained well after five cycles.

In summary this study combines PIL membrane technology with dynamic heterogeneous catalysis (Fenton reaction) to create reusable PILs that address the issue of membrane fouling.

Iron-containing poly(ionic liquid) membranes: a heterogeneous Fenton reaction and enhanced anti-fouling ability, Polym. Chem., 2022,13, 130-138

Link to the paper: https://pubs.rsc.org/en/content/articlelanding/2022/py/d1py01345a

Dr. Kelly Velonia is an Advisory Board Member and a Web Writer for Polymer Chemistry. She joined the Department of Materials Science and Technology in 2007. Research in her group focuses on the synthesis and applications of bioconjugates and biopolymers.