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 °C, respectively, and T g of the MABx‑x segment at 215 °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 ≈660 vol % (590 wt %) with a density change from 1.15 to 1.02 g/cm3. Furthermore, we demonstrated that the film exhibits moisture-responsive behavior within just 10 s upon exposing only one of its surfaces to humid air.