Cationic Alternating Copolymerization of Vinyl Esters and 3-Alkoxyphthalides: Side Chain-Crosslinkable Polymers for Acid-Degradable Single-Chain Nanoparticles

Cationic copolymerization of vinyl acetate and 3-alkoxyphthalides (ROPTs) was demonstrated to proceed using GaCl3 as a Lewis acid catalyst. Both monomers did not undergo homopolymerization, while copolymerization smoothly occurred via the crossover reactions, resulting in alternating copolymers with molecular weights of over 104. The obtained copolymers could be degraded by acid due to the cleavage of the diacyloxymethine moieties, which were derived from the crossover reactions from vinyl acetate to ROPT, in the main chain. An advantage of not radical but cationic copolymerization of vinyl esters was exerted by copolymerizations of radically reactive group-containing vinyl esters with ROPTs. For example, vinyl cinnamate was successfully copolymerized with an ROPT by the cationic mechanism, while keeping the cinnamoyl groups intact. The obtained alternating copolymer was subjected to a photodimerization reaction of the cinnamoyl groups in the side chains, resulting in an acid-degradable single-chain nanoparticle via the intramolecular crosslinking reactions.