Robust monolithic multiscale nanoporous polyimides and conversion to isomorphic carbons†
This paper describes a generalizable approach to the synthesis of monolithic multiscale micro/meso/macro-porous polymers with potential use in catalysis, gas separations and gas storage. The model system is based on hyperbranched polyimides synthesized via an unconventional route from dianhydrides and triisocyanates. Simulations reproducing experimental observables (e.g., XRD, skeletal densities) indicate that relatively small hyperbranched oligomers pack into inherently microporous primary nanoparticles. The latter phase-separate, react through their dangling surface functionality and form robust, monolithic, meso/macro-porous networks. Macroporosity is controlled mainly by the concentration of the reactants; mesoporosity by the chemical identity of the monomers that directs the way particles fill space, e.g., as strings of beads versus globular clusters. Microporosity, being an inherent property of the molecular network, survives pyrolysis and is transferred along with meso and macroporosity to multiscale nanoporous carbons. The materials described herewith are classified as polyimide and carbon aerogels.