Crystallization and multiple melting behavior of a new semicrystalline polyimide based on 1,3-bis(4-aminophenoxy)benzene (TPER) and 3,3′,4,4′-biphenonetetracarboxylic dianhydride (BTDA)

This study introduces a novel high-temperature semicrystalline polyimide, which is based on an ether diamine (TPER or 1,3(4)APB) and BTDA dianhydride, both being commercially available. Phthalic anhydride is used as an endcap for improving thermal stability. The polyimide displays a Tg at ca. 230°C and two prominent melting endotherms at 360 and 416°C, respectively, with a sharp recrystallization exotherm following the lower melting endotherm. Significant recrystallization ability from the melt (at 450°C for 1 min) is observed with cooling rates faster than 200°C/min necessary to quench the polymer into an amorphous state. The effect of small variations in the melt crystallization temperature on the morphology and the melting behavior is discussed. DSC, hot stage polarized optical microscopy and WAXD experiments are utilized to interpret the melting behavior with respect to different causes. Some indirect evidence suggests that the two prominent melting endotherms may be due to different crystal unit cell structures. For crystallization temperatures higher than 350°C, an isothermal lamellar thickening phenomenon occurs with significant increases in the peak melting point (10–14°C) observed for longer crystallization times.