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.