New soluble aromatic polyimides

2,2′-Bis (trifluoromethyl)-4,4′-diaminobiphenyl has been polymerized with pyromellitic dianhydride (PMDA), 3,3′, 4,4′-benzophenometetracarboxylic dianhydride (BPDA), biphenyl-3,3′, 4,4′-tetracarboxylic dianhydride (BPDA), diphenylsulfone-3,3′, 4,4′-tetracarboxylic dianhydride (DSDA), 4,4′-oxydiphthalic anhydride (ODPA), and 4,4′-perfluoroieopropylidinediphthalic anhydride (6FDA) in refluxing m-cresol containing isoquinoline. The polymer prepared from PMDA precipitated during the polymerization. The other polyimides either formed gel-like structures upon cooling to room temperature (BTDA- and BPDA-based) or remained in solution and were precipitated in methanol. The gels formed by the BTDA- and BPDA-based polymers displayed optical properties typical of lyotropic liquid-crystalline solutions. The polymers' intrinsic viscosities ranged from 0.6 to 4.8 dl/g. The Tg's of the polymers prepared from PMDA, BTDA and BPDA could not be detected, while the Tg's of the polymers prepared from DSDA, ODPA and 6FDA ranged from 270 to 320°C. The TGA thermograms of the polymers showed 5% weight losses between 540 and 590°C in air. Fibers have been spun from m-cresol solutions of the BPDA-based polymer that display properties similar to those of aromatic polyamides.