Preparation of novel, high-modulus, swollen- or jungle-gym-type polyimide gels end-crosslinked with 1,3,5-tris(4-aminophenyl)benzene

A novel preparation approach for high-performance polyimide gels that are swollen or have a jungle-gym-type structure is proposed. A new rigid and symmetric trifunctional amine, 1,3,5-tris(4-aminophenyl)benzene (TAPB), was synthesized as a crosslinker. Three different kinds of amic acid oligomers derived from pyromellitic dianhydride (PMDA), 4,4'-oxydiphthalic anhydride (ODPA), p-phenylenediamine (PDA), and 4,4'-oxydianiline (ODA) were end-crosslinked with TAPB at a high temperature to make polyimide networks with different structures. Transparent polyimide gels were obtained from the ODPA-ODA/TAPB series with high compression moduli of about 1 MPa at their equilibrium swollen states in N-methylpyrrolidone. Microscopic phase separation occurred during the gelation-imidization process when polyimide networks were generated from PMDA-PDA/TAPB and PMDA-ODA/TAPB. After these opaque polyimide networks were dried, a jungle-gym-like structure was obtained for the PMDA-PDA/TAPB and PMDA-ODA/TAPB series; that is, there was a high void content inside the networks (up to 70%) and little volume shrinkage. These polyimide networks did not expand but absorbed the solvent and showed moduli as high as those of solids. Therefore, using the highly rigid crosslinker TAPB combined with the flexible monomers ODPA and ODA and the rigid monomers PMDA and PDA, we prepared swollen, high-performance polyimide gels and jungle-gym-type polyimide networks, respectively. (C) 2002 Wiley Periodicals, Inc.