Preparation and Properties of Molecular Composite Films of Block Copolyimides Based on Rigid Rod and Semi-Flexible Segments

Abstract

Molecular composite films of block copolyimides consisting of semi-flexible poly-N,N′-(oxydi-p-phenylene)pyromellitimide (PIOD) and rigid-rod poly-N,N′-(p-phenylene)-pyromellitimide were prepared by the usual two step ring-opening polyaddition and subsequent thermal imidization method, starting from pyromellitic dianhydride and either the aromatic diamines or their N-trimethylsilyl-substituted derivatives. The block copolyimide films were transparent and yellow in color over the whole composition ranges, and changed from brittle to ductile films with increasing PIOD content. As the PIOD content increased, the tensile modulus decreased monotonically, while the elongation at break and fracture energy increased in a similar fashion. The behavior of the tensile strength, however, was rather complicated.