Thermal stability, crystallization kinetics and morphology of a new semicrystalline polyimide based on 1,3-bis(4-aminophenoxy) benzene and 3,3′,4,4′-biphenyltetracarboxylic dianhydride

Abstract

This work investigates the crystallization kinetics and thermal stability of a new melt processable semicrystalline polyimide (T g =210° C, T m =395° C) based on 1,3-bis(4-aminophenoxy) benzene and 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and endcapped with phthalic anhydride. Earlier studies have demonstrated that this polymer is a strong candidate as a structural adhesive for high-temperature and high-performance applications. In this study, an Avrami Analysis was utilized to study the bulk crystallization kinetics as a function of crystallization temperature, melt time and melt temperature. For the crystallization temperatures studied, the Avrami parameter K increased substantially for small increases in undercooling or small decreases in melt temperature and residence time. Spherulitic growth rates were measured microscopically at different crystallization temperatures. The effect of varying the melt time and temperature on the growth rate at a particular temperature was determined. The variation in the Avrami parameters is correlated with independent microscopic observations of the nucleation density and the spherulitic growth rates. Melt viscosity was followed as a function of melt temperature, residence time in the melt and deformation rate. Higher melt temperatures result in a faster increase in the isothermal melt viscosity indicating chemical changes in the polymer at such high melt temperatures. Followed rheologically, onset of crystallization requires greater undercooling when cooling from higher melt temperatures. Non-isothermal crystallization was followed using DSC and optical microscopy, both of which gave evidence of a distinct ‘catastrophic nucleation’ process at temperatures in the vicinity of 330°C during cooling from the melt.