Radical Ring-Opening (Co)Polymerization of Vinyl Oxiranes: Toward Acid-Degradable Backbone Oxygenated-Polystyrene and Polybutadienes.
Abstract
Acid-degradable vinyl polymers prepared by free-radical polymerization (FRP) remain rare despite their potential applications in photoresists, responsive materials, and drug delivery systems. Herein, a series of vinyl oxirane (VO) monomers were designed for radical ring-opening polymerization (rROP) to afford acid-degradable polymers. Among the monomers investigated, VO-1, which features a phenyl substituent at the α-position of the vinyl group, showed superior polymerization behavior, producing polymers with molecular weights up to 31.2 kDa. Density functional theory (DFT) reveals that the significantly enhanced polymerization efficiency arises from the phenyl substitution stabilizing the propagating radical intermediate and promoting epoxide ring-opening. Structural characterization confirmed efficient formation of enol ether linkages along the polymer backbone. VO-1 was also compatible with nitroxide-mediated polymerization. Catalytic hydrogenation of poly(VO-1) yielded an oxygen-containing polystyrene analogue, which can undergo complete depolymerization to give defined small molecules. Copolymerization of VO-1 with 1,3-diene monomers successfully incorporated degradable units into the polymer backbone, and the resulting polymers underwent efficient acid-triggered degradation. The incorporation of VO‑1 also successfully endows the 1,3-dienes-derived elastomer network with acid‑triggered dissolution. This work expands the scope of acid-degradable materials accessible through radical polymerization.