Unzipping and scrambling reaction‐induced sequence control of copolymer chains via temperature changes during cationic ring‐opening copolymerization of cyclic acetals and cyclic esters

Abstract

AbstractA temperature change‐dependent sequence transformation of copolymer chains was demonstrated by a method based on tandem depolymerization and transacetalization reactions during the cationic ring‐opening copolymerization of cyclic acetals and cyclic esters. In this study, the position of polymerization‐depolymerization equilibrium was controlled by the reaction temperature rather than by the decrease in monomer concentration under vacuum conditions, as in our previous study. First, the conditions for efficient copolymerization were optimized, with a particular focus on the structures of cyclic acetals and cyclic esters. Subsequently, sequence transformation induced by temperature change was examined during the copolymerization of 2‐methyl‐1,3‐dioxepane (generated in situ from 4‐hydroxybutyl vinyl ether) and δ‐valerolactone using EtSO3H. The homosequence length of cyclic acetals decreased during depolymerization (unzipping) at the oxonium chain ends upon increasing the temperature from 30 to 90 °C, while transacetalization (scrambling) of the main chain transferred midchain cyclic acetal homosequences to the oxonium chain ends. As a result of the cycle of unzipping and scrambling reactions, an alternating‐like copolymer was obtained. Interestingly, the possibility of reversible sequence transformation upon heating and cooling was also demonstrated.