Poly(amide-ether) Thermoplastic Elastomers Based on Monodisperse Aromatic Amide Hard Segments as Shape-Memory and Moisture-Responsive Materials

A series of high-molecular-weight (M-n up to 29000) multiblock poly(N-methylbenzamide)-b-poly-(ethylene glycol) polymers [poly(MAB(x-x)-b-PEG)], utilizing monodisperse telechelic aromatic N-methylbenzamide-based molecules (MAB(x-x)) (molar mass distribution M-w/M-n = 1.02-1.04) with H2N-PEG-NH2, were successfully prepared via conventional solution polycondensation; their shape memory and moisture-responsive properties were thoroughly investigated. The resultant multiblock copolymers showed three thermal transitions: the glass transition (T-g) and melting (T-m) of the PEG segment at -35 and 55 degrees C, respectively, and T-g of the MAB(x-x) segment at 215 degrees C. Hard opaque pale-yellow films were successfully prepared using the solution-cast method, and several films showed good shape-memory properties, i.e., a shape fixity of 91% and a shape recovery of 97%. These properties were only observed for multiblock copolymer films having both crystalline PEG (degrees of crystallinity from 34.8% to 43.7% were observed) and aggregated monodisperse MAB(x-x) phases. The existence of this cocrystalline structure is critical for the retention of temporary shape at ambient temperature and the recovery of original shape above T-m for the PEG phase in the copolymer film. Upon soaking the film in water for 5 days, it swelled by approximate to 660 vol % (590 wt %) with a density change from 1.15 to 1.02 g/cm(3). Furthermore, we demonstrated that the film exhibits moisture-responsive behavior within just 10 s upon exposing only one of its surfaces to humid air.