Cationic ring-opening copolymerization of a cyclic acetal and γ-butyrolactone: monomer sequence transformation and polymerization–depolymerization control by vacuuming or temperature changes

Polymerization–depolymerization equilibrium is a promising strategy for the construction of polymerization systems through which sustainable polymers can undergo reversible polymer–monomer transformations. In this study, we perform monomer sequence transformation and copolymer depolymerization, which are based on transacetalization reactions and polymerization–depolymerization equilibrium, in the cationic ring-opening copolymerization of 2-methyl-1,3-dioxepane and γ-butyrolactone with a protonic acid. The removal of monomer molecules from the copolymerization solution by vacuuming with a vacuum pump caused monomer sequence to transform into pseudo-alternating copolymer chains and subsequently depolymerize into oligomers. Increasing the temperature during copolymerization also resulted in depolymerization, while copolymers were regenerated by the subsequent decrease in temperature.