Synthesis of High-performance Composites of Poly(4-vinylpyridine-co-styrene) Copolymer (P4VPy–St) and Polyimides (PI) Having Carboxyl Pendant Groups by in-situ Polymerization and Their Mechanical Properties

High-performance composites of poly(4-vinylpyridine-co-styrene) copolymer (P4VPy–St) and polyamic acids (PAA) were prepared by in-situ polymerization. High-performance composites could be obtained from a polymer pair that has an attractive interaction such as a hydrogen bonding interaction. The aggregation of the resulting polyimide (PI) took place easily in the P4VPy–St/PI composite film during the stepwise heat-treatment of the P4VPy–St/PAA composite film to convert PAA to PI. This was because of the disappearance of the carboxyl group due to the imidization of PAA. In this study, free carboxylic acid groups were introduced into the side chains of PI in order to improve the mechanical properties of P4Py–St/PI composites, and the carboxyl group content dependence of the tensile strength of the resulting composite films was investigated. The tensile strength of the resulting composite films increased with increasing carboxyl group content in PI. The hydrogen bonding interaction between the pyridine moiety in the P4VPy–St copolymer and the carboxyl group introduced into PI greatly enhanced both the compatibility and the tensile strength of the composite films.