3-Alkoxyphthalides as Nonhomopolymerizable, Highly Reactive Comonomers for ABC Pseudo-Periodic Terpolymers and Degradable Polymers via Cationic Co- and Terpolymerizations with Oxiranes and/or Vinyl Ethers

Abstract

3-Alkoxyphthalides (ROPTs) are promising candidate monomers that react with a cationic species at the carbonyl group and subsequently undergo ring-opening to generate a carbocation adjacent to both aryl and alkoxy groups (oxocarbenium ion). In this study, cationic polymerizations of ROPTs bearing methoxy, isopropoxy, tertbutoxy, or phenoxy groups were investigated with a particular focus on the copolymerizations with oxiranes. Cationic homopolymerization of ROPTs did not occur under any of the examined conditions. In contrast, cationic copolymerizations of ROPT with oxiranes, such as 4vinyl-1-cyclohexene-1,2-epoxide (VCHO), proceeded smoothly via very frequent crossover reactions. The copolymers could be degraded under acidic conditions due to the cleavage of the acetal moieties generated by the crossover reactions from ROPT to VCHO. Cationic copolymerizations of ROPT with most of the examined vinyl ethers (VEs) and styrene derivatives did not proceed, likely due to inefficient crossover reactions from the vinyl monomers to ROPT. However, cationic terpolymerizations of VE, oxirane, and ROPT successfully proceeded via highly selective crossover reactions, resulting in ABC-type pseudo-periodic terpolymers under optimized conditions.

Sugar-Derived Cyclic Acetals as Comonomers for Cationic Copolymerization with Vinyl Ethers

“…The aryl substituents and/or fused ring structures of X-4 units in copolymer chains are likely responsible for the higher T g s of the CEVE–X-4 copolymers than those of the CEVE–E-1 copolymers and CEVE homopolymer. The VCHO–G-1 copolymer exhibited a lower T g (2 °C; entry 6) than that of a VCHO homopolymer (50 °C; entry 7). In TGA analysis, the copolymers began to degrade at around 200 °C (Figure S27).…”

Organoboron-mediated polymerizations

“…162 In 2023, the same group produced ABC pseudo-periodic terpolymers using 3-alkoxyphthalides as nonhomopolymerizable and highly reactive comonomers. 163 In this terpolymerization process, 3-alkoxyphthalides reacted with a cationic species at the carbonyl group and then underwent a ring-opening process to deliver a carbocation adjacent to both aryl and alkoxy groups. The introduction of the acetal moieties conferred degradability to the polymers under acidic conditions.…”

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

“…ROPTs have a cyclic hemiacetal ester structure and do not exhibit homopolymerizability, which is similar to DOLOs. In our previous study, oxiranes were demonstrated to undergo cationic copolymerizations with ROPTs . In particular, ROPTs exhibited superior copolymerizability to that of DOLOs in terms of polymer MWs and the frequency of crossover reactions.…”

“…In addition, both VAc and IPOPT did not undergo cationic homopolymerization under the conditions suitable for the copolymerization (Table S1). , …”

“…This carbocation (oxocarbenium ion) is stabilized by the electron-donation effects of the adjacent alkoxy and aryl groups. The subsequent reaction of the ROPT-derived carbocation with VAc selectively occurs because ROPTs do not exhibit homopolymerizability . VAc also does not exhibit cationic homopolymerizability; hence, alternating copolymers are produced through continuous crossover reactions.…”