Time resolved WAXS study of the role of mesophase in oriented crystallisation of poly(ethylene terephthalate-co-isophthalate) copolymers

Poly(ethylene terephthalate-co-isophthalate) copolymers containing up to 18 mol% isophalate have been drawn at 90 °C at a deformation rate of ∼15 s−1 while recording two dimensional wide angle X-ray scattering patterns. All polymers, including homopolymer controls, show the development of an oriented smectic mesophase during the last stages of deformation. After the end of deformation, the mesophase decays and is replaced by oriented triclinic crystals which increase according to first order transformation kinetics. The characteristic meridional spacing of the smectic mesophase reduces systematically with increasing isophthalate comonomer and indicates that the comonomer participates in the smectic structure. Unlike isotropic crystallisation from the melt, the crystallinity and crystallisation rate show little variation with comonomer content. This is attributed to the fact that both monomers participate in the intermediate smectic mesophase.