Synthesis and properties of polyimides derived from isomeric biphenyltetracarboxylic dianhydrides

2,2',3,3'-Biphenyltetracarboxylic dianhydride (i-BPDA) was suggested as a monomer for the synthesis of soluble polyimides with high thermal stability, and an efficient method of its preparation has been developed. Polyimides derived from i-BPDA and aromatic diamines (i.e. 4,4'-oxydianiline, 2,2'-bis(trifluoromethyl)benzidine and 9,9'-fluorenylidene-4,4'-dianiline) showed high glass transition (T-g > 330 degrees C) and degradation (T-d5 > 550 degrees C) temperatures, and were soluble in organic solvents (i.e. NMP, DMF, gamma-butyrolacton, CHCl3), although their mechanical properties were inferior to those of polyimides composed of semirigid 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA). Random copolymers, derived from i-BPDA and s-BPDA, retained superior mechanical properties of s-BPDA-based polyimides and showed improved solubilities, depending on the i-BPDA content. A regular increase of glass transition temperatures and a decrease of inherent viscosities of copolymers with increasing content of i-BPDA was observed, whereas the dielectric constants and degradation temperatures were found to be independent of the ratios of dianhydride units. (C) 2000 Elsevier Science Ltd. All rights reserved.