Umpolung Isomerization in Radical Copolymerization of Benzyl Vinyl Ether with Pentafluorophenylacrylate Leading to Degradable AAB Periodic Copolymers

Abstract

This study revealed benzyl vinyl ether (BnVE) shows the peculiar isomerization propagation in radical copolymerization with an electron‐deficient acrylate carrying pentafluorophenyl group (PFA). The comonomer pair inherently exhibits the cross‐over propagation feature due to the large difference in electron density. However, the radical species of PFA was found to undergo a backward isomerization to the penultimate BnVE pendant giving benzyl radical species prior to the propagation with BnVE. The isomerization brings a drastic change in the character of growing radical species from electrophilic to nucleophilic, and thus the isomerized benzyl radial species propagates with PFA. Consequently, the two monomers were consumed in the order of AAB (A: PFA; B: BnVE) and the unique periodic consumption was confirmed by the pseudo‐reactivity ratios calculated by the penultimate model: r11 = 0.174 and r21 = 6600 for PFA (M1) with BnVE (M2). The pentafluorophenyl ester groups of the resulting copolymers are transformed into ester and amide groups via alcoholysis and aminolysis post‐polymerization modifications. The unique isomerization in AAB sequence allowed the periodic introduction of benzyl ether structure in the backbone leading to efficient degradation under acid conditions.