Radical Ring-Opening Polymerization : A tool for plastic’s degradation

Low weight, low price and excellent stability over time are the main advantages of polymers (also known as "plastics"), which explain their massive use in a wide range of applications, including packaging, construction and the automotive industry. In 2019, global plastics production is estimated at 370 million tonnes. Among the various families of organic materials, vinyl polymers occupy an important place. These polymers are obtained by chain polymerization processes leading to carbon skeletons of the C-C type, which are therefore non-(bio)degradable. However, their high post-use stability and poor waste management pose major environmental problems today. Microplastics, resulting from the partial fragmentation of certain polymers, are a major source of ocean pollution. Given that it is very difficult and costly to design entirely new materials that can have both the desired properties (mechanical, thermal, solvent resistance, etc.) and be recyclable and/or biodegradable at the end of their life cycle, it seems worthwhile to transform already known materials into biodegradable/recyclable equivalents. This approach is based on the introduction of cleavable bonds into the polymer backbone so that degradation (by hydrolysis, for example) produces oligomers which can then be recycled and/or bioassimilated by micro-organisms.

An effective method for incorporating weak bonds randomly into the C-C backbone of a vinyl polymer is the copolymerization of vinyl monomers with cyclic monomers by ring-opening radical polymerization (rROP). This method combines the advantages of ring-opening and radical polymerization, i.e. the production of polymers with heteroatoms and/or functional groups in the main chain, with the robustness, ease of use and gentle polymerization conditions of a radical process. Polymerization takes place through the addition of radicals to cyclic monomers bearing exo-methylene functions or equivalent groups, followed by fragmentation of the intermediate cyclic radical to give a new radical and incorporation of heteroatoms into the C-C backbone. The introduction of these cleavable functions will enable post-use degradation of plastics.

This article presents the rROP principle, the main families of cyclic monomers copolymerizable with vinyl monomers, and the main applications of the resulting (bio)degradable materials (polymers for packaging, latex and degradable surfaces, 3D printing, biomaterials and water-soluble polymers).