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This work details a novel polyurethane liquid crystal elastomer (PULCE) with exchangeable carbamate functional groups that enable programming of a uniformly aligned monodomain sample through the application of external stress and simultaneous activation of dynamic bond exchange of the carbamate. PULCEs were synthesized using a thiol-Michael addition reaction, and the reversion of the carbamate group was observed by real-time FT-IR and mechanical analysis. Two independent phase transitions (isotropic–nematic and nematic–smectic) were employed to actuate two-way autonomous strains and multiple shape memory effects in a single system. In addition, thermally activated bond exchange engineered into the network transformed the permanent configuration of the material into various complex shapes. The programmed network topology and bond exchange conditions controlled the two-way autonomous shape changes. Coupling the shape memory effect of the polymer network with the plasticity induced by the thermally activated dynamic covalent chemistry in shape changing and shape memory materials will expand their applications and capabilities in emerging multifunctional devices.
Wen et al. (Wed,) studied this question.