ISOMERIC COMPOSITIONS IN AMIDE ACIDS AND POLY(AMIC ACID)S DERIVED FROM 1-(TRIFLUOUOMETHYL)-2,3,5,6-BENZENETETRACARBOXYLIC DIANHYDRIDE

Two different poly(amic acid)s were synthesized by the polycondensatio ns of 1-(trifluoromethyl)-2,3,5,6-benzenetetracarboxylic dianhydride ( CF3DAN) with p-phenylene diamine and benzidine. In addition, an amide acid model compound was prepared from CF3DAN and aniline. Isomeric uni ts in the poly(amic acid)s as well as the amide acid were investigated by H-1 and C-13-nuclear magnetic resonance (NMR) spectroscopies. Spec troscopic results indicate that the major isomeric component was a CF3 -meta-isomeric unit centered on the aromatic carbon substituted with t he trifluoromethyl group. In particular, the amide acid compound was d etermined to be composed of 80 mol % CFS-meta-isomer and 20 mol % H-me ta-isomer. Therefore, for the poly(amic acid)s, the minor isomeric com ponent is speculated to be a H-meta-isomeric unit rather than a para-i someric unit. The result might result mainly from the strong electron- withdrawable and bulky trifluoromethyl substituent in the CF3DAN monom er. The strong electron withdrawability might significantly enhance th e reactivities of the adjacent carbons in the monomer to the nucleophi lic attack of the amino nitrogen in the aniline and diamines, and cons equently overcome the role of the bulkyness, ultimately leading to the amide acid and poly(amic acid)s rich with the CF3-meta-isomeric unit. In addition, a portion of the imide form was detected in the dried AN -CF3DAM-AN amide acid. Thus, the formation of imide linkage might be i nvolved in a small portion for the dried poly(amic acid)s. (C) 1998 Jo hn Wiley & Sons, Inc.