New organosoluble and thermally stable poly(amide-imide)s with benzoxazole or benzothiazole pendent groups: Synthesis and characterization

Abstract

Two new benzoxazole or benzothiazole-containing diimide-dicarboxylic acid monomers, such as 2-[3,5-bis(N-trimellitimidoyl)phenyl]benzoxazole (2o) or 2-[3,5-bis(N-trimellitimidoyl)phenyl]benzothiazole (2s) were synthesized from the condensation reaction between 3,5-diaminobenzoic acid and 2-aminophenol or 2-aminothiophenol in polyphosphoric acid (PPA) with subsequent reaction of trimellitic anhydride in the presence of glacial acetic acid, respectively, and two new series of modified aromatic poly(amide-imide)s were prepared. This preparation was done with pendent benzoxazole or benzothiazole units from the newly synthesized diimide-dicarboxylic acid and various aromatic diamines by triphenyl phosphite-activated polycondensation. In addition, the corresponding unsubstituted poly(amide-imide)s were prepared under identical experimental conditions for comparative purposes. Characterization of polymers was accomplished by inherent viscosity measurements, FT-IR, UV-visible, 1H-NMR spectroscopy and thermogravimetry. The polymers were obtained in quantitative yields with inherent viscosities between 0.39 and 0.81dlg-1. The solubilities of modified poly(amide-imide)s in common organic solvents as well as their thermal stability were enhanced compared to those of the corresponding unmodified poly(amide-imide)s. The glass transition temperature, 10% weight loss temperature, and char yields at 800°C were, respectively, 7-26°C, 17-46°C and 2-5% higher than those of the unmodified polymers. © 2010 John Wiley & Sons, Ltd.