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 H 2 N-PEG-NH 2, 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 MAB x-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/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.