SYNTHESIS, STRUCTURE, AND PROPERTIES OF HIGH-PERFORMANCE ALTERNATING COPOLYIMIDES

A new diamine monomer, 2,5-(diisopropoxycarbony)benzene-1,4-dicarboxam ide was synthesized. Using the diamine, several alternating copolyimid e precursors were successfully synthesized by its condensation polymer ization with dianhydrides. The structure and properties (mechanical pr operties and thermal expansivity) of alternating copolyimides imidized thermally were characterized, and compared with those of the correspo nding random copolyimides prepared from the copoly(amic acid)s. The al ternating copolyimides exhibited relatively higher chain order and in- plane orientation in films than the random copolyimides. The higher ch ain order and in-plane orientation led to the higher tensile modulus a nd lower thermal expansivity in the alternating copolyimides. Such eff ect of comonomer sequence was found to be highly pronounced in copolyi mides consisting of comonomers which have a large difference in the ch ain rigidity. It was demonstrated in this study that the formation of alternating copolyimides is a suitable route to improve the performanc e of properties.