Hygromorphic Polymers: Synthesis, Retro-Michael Reaction, and Humidity-Driven Actuation of Ester–Sulfonyl Polyimides and Thermally Derived Copolyimides

With a view toward broadening the adaptive capability of polyimide-based systems that have been shown to be mechanically responsive to light, heat, and thermal-electrical stimuli, a simple diamine containing a highly polar ester–sulfonyl (ES) pendant was synthesized via a two-step route. It was polymerized with five common dianhydrides in N-methylpyrrolidinone to afford poly(amic acid), PAA, solutions, which were subsequently converted to a series of amorphous polyimides containing ester–sulfonyl (−CH2CH2SO2Me) pendants, generically designated as PI-ES, by either chemical imidization at room temperature in the same pot or heat treatment of PAA cast film at 175 °C. The chemically imidized polyimide films are tough and creasable, but the thermally imidized ones are brittle because of much lower molecular weights (GPC results). In addition, a series of thermally derived copolymers designated as PI-ES:A, which contains ES and carboxylic acid (A) pendants, were prepared from PI-ES via a retro-Michael reaction ...