Shape memory hyperbranched polyurethanes via thiol-ene click chemistry

Hyperbranched poly(amine-ester) (Hyper OH) was synthesized from pentaerythritol tetraacrylate (PETTA) and diethanolamine (DEA) by Michael addition reactions. One-to-one stoichiometric reaction between diisocyanatodicyclohexylmethane (H12MDI) and 2-hydroxyethyl acrylate (HEA) produced dimmers carrying both NCO and vinyl groups at two chain termini, which were subsequently reacted with Hyper OH to form hyperbranched polymers (HBP, Hyper 8). Replacing HEA by trimethylolpropane diallyl ether (TMPDE) produced Hyper-16. On the other hand, polyurethane prepolymers were synthesized from H12MDI and polyol, end capped with 1,2-ethanedithiol, and UV cured to synthesize crosslinked polyurethanes via thiol-ene click chemistry. Hyperbranched polymers acted as multifunctional crosslinkers as well as reinforcing fillers and significantly enhanced mechanical, thermal and shape memory properties. Effects were more pronounced with thiol-ene click chemistry than ene-ene curing.