Sequence-Controlled Cationic Terpolymerization of Styrene Derivatives, Oxiranes, and Aromatic Aldehydes: Synthesis of Acidically or Oxidatively Degradable Terpolymers

In this study, we investigated the cationic terpolymerization of styrene derivatives, oxiranes, and aromatic aldehydes to achieve precise sequence control. Cationic terpolymerization of p-methoxystyrene (pMOS), 1,2-epoxy-4-vinylcyclohexane (VCHO), and benzaldehyde (BzA) proceeded via crossover reactions, yielding terpolymers with high molecular weights (MWs). In addition, selective crossover reactions consisting of pMOS → VCHO, VCHO → BzA, and BzA → pMOS proceeded, resulting in terpolymers with controlled [(pMOS)x–(VCHO)y–BzA]n sequences. The BzA-derived propagating end, which has a structure similar to that of the styrene-derived propagating end, was important for effective terpolymerization as judged by inefficient crossover reactions using methyl ethyl ketone instead of benzaldehyde. By optimizing polymerization conditions, homopropagation reactions of styrene derivatives and oxiranes were almost suppressed in the terpolymerization of 4-tert-butoxystyrene, VCHO, and 2,4-dimethoxybenzaldehyde, resulting in terpolymers with ABC-type periodic sequences. The terpolymers were degraded into low-MW products by acid or oxidant via the cleavage of the crossover reaction-derived, secondary benzylic ether moieties in the main chain.