Thermal behaviour and morphology of homogeneous ethylene-1-octene copolymers with high comonomer contents

The thermal behaviour and morphology of a series of homogeneous ethylene-1- octene copolymers, covering a wide range of 1-octene content up to 44 mole% , is studied using differential scanning calorimetry (DSC), time-resolved s mall-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). The influence of the comonomer (1-octene) content, as well as the influenc e of the comonomer type (branch length) are investigated by comparison with previous results on homogeneous ethylene-propylene and ethylene-l-butene c opolymers. Special emphasis is put on copolymers with high comonomer conten ts or low densities (<870 kg/m(3)) at room temperature. The thermal behavio ur and the morphology of the present copolymers reveal no discontinuities w ith increasing comonomer content and support a model in which the morpholog y changes gradually from a lamellar base morphology into a granular one con sisting of small blocky structures and, possibly via fringed-micelles, into a morphology consisting of loosely packed ethylene sequences. The latter s tructures are too small and/or too imperfect to be detected by WAXD. Howeve r, SAXS and DSC are sensitive to them and are useful techniques over the wh ole comonomer content range. (C) 2000 Published by Elsevier Science Ltd. Al l rights reserved.