Melt-Processable Semicrystalline Polyimides Based on 1,4-Bis(3,4-dicarboxyphenoxy) benzene Dianhydride (HQDPA): Synthesis, Crystallization, and Melting Behavior

It is a great challenge to develop semicrystalline polyimides exhibited significant recrystallization ability and fast crystallization kinetics from the melt. A series of semicrystalline polyimides based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride HQDPA) and different diamines, including 1,3-bis(4-aminophenoxy) benzene (TPER), 1,4-bis(4-aminophenoxy) benzene (TPEQ), 4,4'-oxydianiline (4,4'-ODA) and 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), end capped with phthalic anhydride were synthesized. Crystallization and melting behaviors were investigated by differential scanning calorimetry (DSC). The polyimide derived from HQDPA/TPER (PI-1) exhibited a glass transition temperature (T-g) at 190 degrees C and double melting temperatures (T(m)s) at 331 degrees C and 350 degrees C, and the polyimide derived from HQDPA/TPEQ (PI-2) displayed a T-g at 214 degrees C and a T-m at 388 degrees C. PI-1 and PI-2 showed significant recrystallization ability from melt and high crystallization rate by isothermal crystallization kinetics study, while polyimides based on 4,4'-ODA and BAPB lost crystallizability once taken to the melt. These polyimides also exhibited excellent thermo-oxidative stability with 5% weight loss temperature higher than 500 degrees C and good mechanical properties with tensile moduli of 2.0-3.3 GPa, tensile strengths of 85-105 MPa and elongations at break of 5-18%. PI-1 also possessed outstanding melt flowability with less than 300 Pa .s around 370 degrees C by rheological measurements