Crystallization kinetics of copoly(ester imide)s derived from PBT, trimellitic anhydride, and aliphatic diamines

Abstract

The crystallization kinetics of copoly(ester imide)s based on poly(butylene terephthalate) (PBT), trimellitic anhydride, and diaminobutane (PEI-4), resp. diaminohexane (PEI-6) or diaminoethane (PEI-2) are investigated by means of time-resolved x-ray scattering employing synchrotron radiation. The PEI-4 and PEI-6 copolymers exhibit a remarkably high degree of crystallinity, which can be attributed to the formation of mixed crystals in the co-PEI-4 and to blockiness in the case of co-PEI-6. Whereas the pure PEI-4 forms large negatively birefringent spherulites, the co-PEI-4 and the PEI-6 homo- and copolymers form much smaller superstructures like axialites or ellipsoids. In the co-PEI-4 and co-PEI-6, the rate of crystallization is slower compared to the homopolymers due to the incorporation of the respective comonomer unit. The PEI-4 forms a second crystal modification upon drawing and subsequent crystallization, probably with a monoclinic unit cell. The PEI-6 crystallizes faster than PEI-4 due to the improved flexibility of the longer diamine component. In contrast, the crystallization of PEI-2 and its copolymers takes several hours and the equimolar co-PEI-2 remains completely amorphous.