The majority of today plastics are non-degradable and derived from fossil feedstock. Contamination of water bodies and the rest of the environment with these plastic wastes is a problem of concern that has been faced using different sustainable approaches. Synthesis of degradable plastics is one of the alternatives. However, polymerization reaction conditions and the corresponding monomers sequence control are hurdles that need to be overcome.
Biobased polyesters1 as poly(lactic acid) (PLA) are commercially successful sustainable polymers derives from renewable feedstocks such as corn. However, their use is limited due to its fragility. Therefore, selective copolymerization may improve their practical use.
Ring-opening polymerization (ROP) consists in using cyclic monomers instead of linear ones. The advantage of this polymerization is the mild reaction conditions involved that allows selectivity regarding the monomers addition to the polymerization chain.
ROP monomers are cyclic esters, epoxides combined with heteroallenes, cyclic anhydrides with epoxides and o-carboxyanhydrides. These cyclic monomers have been mentioned in reactivity order: o-carboxyanhydrides (O) are quite more reactive than cyclic esters (C).
A self-switchable synthesis protocol2 is based in this reactivity difference. For instance, if a target polymer consists on sequence of the last two monomers: O and C, one-pot/one-step equivalent molar combination of them might lead to: -(O-O-O)n-(C-C-C)n- , since O will react faster with itself than with C.
This strategy of polymerization can be applied also sequentially instead of in one-pot depending on the polymer characteristics required. Self-switchable strategy is still being developed and external factors on the polymer synthesis as solvent, catalyst, CO addition, reducing agents, electrochemical fields and light are fundamental to obtain the desired polymer characteristic.
Other monomers as cyclic carbonates, Isocyanates with epoxides, carbon monoxide and cyclic monomers containing sulfur are proposed2 to be tested in self-switchable polymerization.
1.- Q. Zhang, M. Song, Y. Xu, W. Wang, Z. Wang, L. .Zhang, Prog. Polym. Sci.,
120 (2021) 101430
2.- C. Hu, X. Pang, X. Chen Macromolecules. https://doi.org/10.1021/acs.macromol.2c00085
