Robust monolithic multiscale nanoporous polyimides and conversion to isomorphic carbons

Abstract

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.

Density and shrinkage as guiding criteria for the optimization of the thermal conductivity of poly(urethane)-class aerogels

“…For all monomers, samples shrank up to 40% less as the monomer concentration increased, likely due to a higher degree of cross-linking between polymer strands. Overall, the shrinkage of our PUR-PIR aerogels is comparable or somewhat lower than reports on polymeric aerogels, where shrinkages of up to 46% have been reported [27][28][29][30]. We also note that freeze-drying did not induce a large difference in shrinkage compared with the literature reports (where aerogels were supercritically dried), indicating that shrinkage is mostly due to the interaction between polymer strands during processing and drying.…”

Synthesis and biomedical applications of aerogels: Possibilities and challenges

“…polyurea [144], polyimides [145], polyamide [146], polyacrylonitriles [127], polyurethanes [147], polystyrene [148], polybenzoxazine [149], poly(dicyclopentadiene) [150], etc.…”

Exceptionally High CO2 Adsorption at 273 K by Microporous Carbons from Phenolic Aerogels: The Role of Heteroatoms in Comparison with Carbons from Polybenzoxazine and Other Organic Aerogels

“…The most well‐known carbon aerogels have been obtained from pyrolysis of resorcinol‐formaldehyde (RF) aerogels . The backbone of RF aerogels is a phenolic resin; however, many other classes of polymeric aerogels yield carbon aerogels, including polyureas, polyamides, polyimides, polyurethanes, and polybenzoxazines (PBOs) . The latter are considered a sub‐class of phenolic aerogels with Mannich bridging between phenolic moieties rather than the typical methylene bridging of RF aerogels.…”