Synthesis and Evaluation of Thermally Curable Hyperbranched Polymers with Low Glass Transition Temperature

Abstract

Thermosetting hyperbranched polymers were synthesized by radical copolymerization of dodecyl methacrylate and ethyleneglycol dimethacrylate in the presence of an addition-fragmentation chain transfer agent, methyl 2-(bromomethyl) acrylate. The resulting polymers had a branched structure containing multiple end groups per one polymer chain. By changing the comonomer compositions and the stoichiometric ratio of the total comonomer to the addition-fragmentation chain transfer agent, the glass transition temperatures of the resulting hyperbranched polymers can be controlled in a wide range from -80 ℃ to 13 ℃. The hyperbranched polymer contains multiple vinyl groups, i.e., side-chain vinyl groups (methacryloyl group) derived from ethyleneglycol dimethacrylate unit and ω-end vinyl groups (2-methoxycarbonyl-2- propenyl group) generated by addition-fragmentation chain transfer. Therefore, the hyperbranched polymers underwent spontaneous polymerization above ca. 100 ℃, and exhibited thermosetting properties even in the absence of a radical curing agent. The glass transition temperatures of the hyperbranched polymers were significantly increased to 130 ℃ or higher by thermal curing at 180 ℃for 1 h.