The effect of liquid crystal fillers on structure and properties of liquid crystalline shape memory polyurethane composites II: 4-hexadecyloxybenzoic acid

In order to better understand the interrelation between liquid crystal fillers and functional polymers, a series of liquid crystalline shape memory polyurethane composites (LC-SMPUCs), named shape memory polyurethane (SMPU)–4-hexadecyloxybenzoic acid (HOBA) composites, are prepared by incorporating HOBA into SMPU based on a polyethylene glycol (PEG) soft segment. The results demonstrate that the dimerization structure of HOBA is maintained in the as-prepared SMPU–HOBA composites, facilitating liquid crystalline properties. Characterization results display smectic C phase upon heating, while the isotropic temperature shifts to a higher temperature, broadening the temperature range of the liquid crystalline phase. The SMPU–HOBA composites form a two-phase separated structure containing a SMPU phase and a HOBA phase; the incorporated HOBA can promote crystallizability of both soft and hard segments of SMPU, while crystalline hard phases are maintained within the high temperature range. Thus, SMPU–HOBA composites demonstrate a two-step modulus change upon heating that releases a triple-shape memory effect. The final shape fixing ratio is higher than 99%, and the final shape recovery ratio reaches 90%. Therefore, the SMPU–HOBA composites successfully provide a desirable combination of liquid crystalline properties and triple-shape memory properties, making them ideal candidates for smart sensor, smart labels, etc.