Organo-soluble polyimides: synthesis and characterization of polyimides containing phenylated p-biphenyl and p-terphenyl units

4,4'-diamino-2,2'-diphenylbiphenyl (1), 4,4''-diamino-2',3',5'-triphenyl-p-terphenyl (2a) and 4,4''-diamino-2',3',5',6'-tetraphenyl-p-terphenyl (2b) have been polymerized with several aromatic dianhydrides in refluxing m-cresol containing isoquinoline to afford a series of phenylated polyimides. The polymerization mixtures of 1 and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 3,3'4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and of 2a and pyromellitic dianhydride (PMDA) set to gel-like structures upon cooling. The gels, which displayed optical anisotropy typical of a liquid crystalline-like phase, could be dissolved by heating and re-formed by cooling. Although the p-catenated, rigid-rod polymers obtained from the diamines and PMDA were only soluble in concentrated sulphuric acid, the polymers that were prepared from 1 and 2a and 3,3',4,4'-diphenylethertetracarboxylic dianhydride (ODPA), 3,3',4,4'-diphenylsulphonetetracarboxylic dianhydride (DSDA) and 2,2-bis[4(1 ,2-dicarboxyphenyl)]-1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA) were soluble in N-methyl-2-pyrrolidinone (NMP), m-cresol and chlorinated solvents. In general, polymers prepared from 2a were the most soluble, while polymers prepared from 2b were the least soluble. The intrinsic viscosities of the polymers ranged from 0.61 to 5.1 dl g(-1) in concentrated sulphuric acid or NMP at 30 degrees C. The glass transition temperatures of most of the polymers could not be detected with differential scanning calorimetry. The temperatures at which the polymers underwent 5% weight losses when subjected to thermal gravimetric analysis ranged from 500 to 600 degrees C in both air and nitrogen. Several of the polymers could be solution cast into thin, water-white flexible films.