Synthesis and properties of AB-Type semicrystalline polyimides prepared from polyamic acid ethyl ester precursors

Three AB-type polyimides with para-, meta- and ortho-linked main chain unit s based on hydroquinone, resorcinol and catechol, were synthesized and char acterized. The polyimides were prepared in two steps by the direct polycond ensation reactions of isomeric monomers, 4-(4-aminophenoxy)diphenyl ether-3 ',4'-dicarboxylic acid monoethyl ester (I-p), 3-(4-aminophenoxy)diphenyl et her-3',4'-dicarboxylic acid monoethyl eater (I-m) and 2-(4-amiaophenoxy)dip henyl ether-3',4'-dicarboxylic acid monoethyl ester (I,), to form poly(amic acid ethyl ester)s followed by thermal or chemical imidization. The result ant polyimides were analyzed by tensile tests, thermogravimetry (TG), diffe rential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and wide-angle X-ray diffraction measurements. It was shown that these AB-type polyimides were semicrystalline and the crystallinities were estimated to b e 19-24%. These polyimides showed glass transition temperatures in the rang e of 178-198 degreesC and melting transition temperatures of 308-393 degree sC. DSC measurements suggested that the polyimide based on hydroquinone uni ts crystallizes much Easter than those based on resorcinol and catechol. Th e polyimide based on the fully para-ether linkages showed a single melting endotherm, whereas the polyimides containing meta-and ortho-ether linkages exhibited bimodal melting behavior.