Crystallization and Multiple Melting Behavior of a New Semicrystalline Polyimide based on 1,3-bis (4-aminophenoxy) benzene (TPER) and 3,3’, 4,4’-benzophenonetetracarboxylic dianhydride (BTDA)

This study addresses the crystallization and multiple melting behavior of a new high temperature semicrystalline polyimide, which is based on an ether diamine (TPER or 1,3 (4) APB) and BTDA dianhydride, both of which are commercially available. It also uses phthalic anhydride to endcap the chains thus improving thermal stability. The polyimide displays a Tg at ca. 230°C and two prominent melting endotherms at 360°C and 416°C respectively, with a sharp recrystallization exotherm immediately after the lower melting endotherm. The polyimide is able to crystallize even after exposure to high melt temperatures of 450°C (for 1 min) and displays fast crystallization kinetics with cooling rates larger than 200°C/min necessary to quench the polymer into an amorphous state. Additionally, the melting behavior is tremendously influenced by small variations in the melt crystallization temperature. A small melting shoulder appears ca. 10-15°C above the crystallization temperature (for Tc ≤ 345°C), while only one prominent higher melting endotherm is observed for Tc ≥ 350°C. DSC, hot stage polarized optical microscopy and WAXD experiments are utilized to interpret the melting behavior. Indirect evidence suggests that the two prominent melting endotherms are due to different crystal unit cell structures. The prominent multiple melting endotherms represent the melting of primary crystals formed at the crystallization temperature and are not a consequence of a ‘continuous’ melting and recrystallization process. For temperatures