Poly(ethylene terephthalate-co-isophthalate) copolymers containing up to 18 mol% isophalate have been drawn at 90 degrees C at a deformation rate of similar to 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. (c) 2005 Elsevier Ltd. All rights reserved.