Patent ID: 9676915
Date: 2017-06-13
CPC Classifications: C08G,C08J

Claim:
1. A process for preparing a foam comprising a porous polyimide network or porous particles comprising a polyimide network, the process comprising: reacting a polyisocyariate having on average at least two isocyanate groups per molecule and a polycarboxylic acid comprising a polycarboxylic acid having at least three COOH groups per molecule or anhydride thereof and optionally, comprising a polycarboxylic acid having two COOH groups per molecule or anhydride thereof, in the presence of a solvent and a catalyst to obtain a reaction mixture comprising a hyperbranched polyimide; continuing the reaction until at least one hyperbranched polyimide having a molecular weight such that precipitation of the at least one polyimide in the form of porous particles from the solvent results and a suspension of porous particles in the solvent is obtained; separating the porous particles from the solvent and drying the separated porous particles to obtain the porous particles comprising a polyimide network: or evaporating the solvent from the suspension to form the foam comprising the porous polyimide network; and drying the foam; wherein the polyimide of the separated porous particles and the polyimide of the porous polyimide network have residual carboxylic acid and isocyanate functional groups, crosslinking of the residual functional groups produces a porous network of crosslinked polyimide, and wherein the catalyst is water.