A polyester–polystyrene hybrid connected by dynamic covalent bonds prepared via radical polymerization of styrene in a “RAFT gel”

Abstract

We demonstrate a new method for hybridization of an aliphatic polyester-based gel with a vinyl polymer via dynamic covalent bonds. First, we synthesized poly[(butylene thiomalate)-co-(butylene adipate)] (M_n = 1.1 × 10⁴; M_w/M_n = 1.5) containing pendent mercapto groups by chemoselective dehydration polycondensation of 1,4-butanediol, thiomalic acid, and adipic acid. Next, we cross-linked the polyester chains with 1,1-thiocarbonyldiimidazole to form a reversible addition–fragmentation chain-transfer (RAFT) gel, in which the trithiocarbonate moiety acted as a cross-linker as well as a chain transfer agent. The “RAFT gel” was then swollen in vinyl monomers including styrene, methyl methacrylate, N-isopropylacrylamide, and methyl acrylate, and styrene was radically polymerized within the gel. A transparent hybrid film was thereby prepared after drying under reduced pressure. Differential scanning calorimetry and dynamic mechanical analysis measurements confirmed that the polyester and polystyrene segments were miscible at the segment level (50 μm level). Subsequent aminolysis of the trithiocarbonate moieties of the hybrid gel afforded poly[(butylene thiomalate)-co-(butylene adipate)]-graft-poly(styrene) (M_n = 5.7 × 10⁴, M_w/M_n = 5.2). We characterized the molecular weight of the branches (M_n = 0.57 × 10⁴, M_w/M_n = 1.6) after saponification of the polyester backbone, which was a narrower molecular-weight distribution than that in the absence of the RAFT gel (M_n = 3.4 × 10⁴, M_w/M_n = 3.8). The results indicate that the trithiocarbonate cross-links in the gel had acted as the chain-transfer agent.