Polyester‐polyether block copolymers. I. Wide‐angle X‐ray diffraction studies of poly(hexamethylene terephthalate)/poly(oxytetramethylene) and related block polymers

The crystallisation and orientation of the individual structural components of poly(hexamethylene terephthalate)/poly(oxytetramethylene) block copolymers have been studied by wide‐angle X‐ray diffraction. The crystallisation behaviour in the unstretched state is determined by the proportions and molecular weights of the polyether blocks. For copolymers containing less than 60 wt% of polyether of m. w. ≯ 2000, only the polyester segments crystallise spontaneously, but with polyether m. w > 2000 two crystalline phases are formed. Similar behaviour was found in block polymers from other readily crystallising polyesters, but with non‐crystallising polyesters the polyether segments crystallised spontaneously. Moderate tensile deformation of the block copolymers from polyether of m. w. 2000 leads to the stress‐reversible highly oriented crystallisation of the polyether whilst the polyester remains undeformed. At higher extensions, irreversible orientation of the polyester segments occurs. The observations suggest that the polyester and polyether segments form discrete regions since otherwise homogeneous crystallisation should occur.