Thermal Stability, Crystallization Kinetics and Morphology of a New Semicrystalline Polyimide based on 1,3-bis (4- aminophenoxy) benzene (TPER) and 3,3’, 4,4’- biphenyltetracarboxylic dianhydride (BPDA)

This work investigates the crystallization kinetics and thermal stability of a new melt processable semicrystalline polyimide (Tg= ca. 210°C, Tm= ca. 395°C) based on 1,3bis(4-aminophenoxy) benzene (TPER) and 3,3’,4,4’-biphenyltetracarboxylic dianhydride (BPDA), and endcapped with phthalic anhydride (PA). Earlier studies have demonstrated that this polymer is a strong candidate as a structural adhesive for high temperature and high performance applications. This study deals with the thermal stability, the effect on crystallization kinetics, and the crystalline morphology of the polymer when exposed to melt temperatures in excess of 410°C for various residence times. In the present study, an Avrami analysis was utilized to study the overall bulk crystallization kinetics after a specific thermal history. The Avrami exponent (n) slightly increased and the parameter ‘K’ decreased with increasing supercooling. Also, Avrami analysis (at 355°C) was utilized to evaluate the effect of melt temperature (from 410°C to 450°C) and effect of melt residence time (2 min to 30 min at 430°C) on the crystallization kinetics. The increase in melt temperature led to an increase in the value of Avrami exponent while the value of parameter ‘K’ dropped significantly. Although the melt residence time did not have much effect on the Avrami exponent, a significant drop in the value of parameter ‘K’ was observed with increasing residence time in the melt. To evaluate the thermal stability, melt viscosity was followed at 430°C as a function of frequency. The melt displayed shearthinning behavior with a significant drop in viscosity with increasing frequency. Also, the isothermal viscosity at lower frequencies increased by nearly an order of magnitude after ca. 20 minutes at 430°C. Isothermal time sweeps of the melt viscosity were carried out at