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, w hich is based on an ether diamine (TPER or 1,3(4)APB) and BTDA dianhydride, both bring commercially available. Phthalic anhydride is used as an endcap for improving thermal stability. The polyimide displays a T-g at ca. 230 d egreesC and two prominent melting endotherms at 360 and 416 degreesC, respe ctively, with a sharp recrystallization exotherm following the lower meltin g endotherm. Significant recrystallization ability from the melt (at 450 de greesC for 1 min) is observed with cooling rates faster than 200 degreesC/m in necessary to quench the polymer into an amorphous state. The effect of s mall variations in the melt crystallization temperature on the morphology a nd the melting behavior is discussed. DSC, hot stage polarized optical micr oscopy 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 degreesC, an i sothermal lamellar thickening phenomenon occurs with significant increases in the peak melting point (10-14 degreesC) observed for longer crystallizat ion times. (C) 2001 Elsevier Science Ltd. All rights reserved.