Sequence-Controlled Terpolymers with Multistep Degradability by Cationic Terpolymerization of Vinyl Ethers, Styrene Derivatives, and Aldehydes

Abstract Devising strategies to control multiple factors of polymer chains, such as molecular weight, monomer sequence, and degradable moieties, is essential for the creation of polymers with precisely tailored properties. In this study, we investigated cationic terpolymerization of vinyl ethers (VEs), styrene derivatives, and conjugated aldehydes toward the synthesis of acidically degradable terpolymers with controlled monomer sequences. Many conjugated aldehydes, such as benzaldehyde derivatives, are nonhomopolymerizable due to the very low ceiling temperatures. In the terpolymerization of 2-chloroethyl VE, p-methoxystyrene, and p-methylbenzaldehyde, terpolymers with statistical-type sequences containing isolated aldehyde units were obtained due to comparable reactivities of 2-chloroethyl VE and p-methoxystyrene. Molecular weights of the terpolymers were also controlled because the polymerization proceeded in a living manner. When isobutyl VE and p-methoxystyrene were used, a block-type terpolymer consisting of an isobutyl VE–aldehyde alternating block and a p-methoxystyrene–aldehyde block was obtained due to the much higher reactivity of isobutyl VE relative to p-methoxystyrene. These terpolymers exhibited acid-dependent degradability arising from the different stabilities of acetal moieties and secondary benzylic ether moieties in the main chains. Terpolymers exhibiting temperature-dependent degradability, derived from acyclic and cyclic acetal moieties, were also synthesized by terpolymerization of VE, cyclic enol ether, and aldehyde.