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

The thermal behaviour and morphology of series of homogeneous ethylene-prop ylene and ethylene-l-butene copolymers, which cover wide ranges in comonome r content, are studied by differential scanning calorimetry (DSC), time-res olved small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WA XD) and transmission electron microscopy (TEM). The thermal behaviour and t he morphology of the copolymers change in a continuous way as the comonomer content is increased, supporting the model in which the morphology changes gradually from a lamellar base morphology into a granular one consisting o f small block-shaped structures. When the comonomer amount is raised furthe r to very high contents, possibly via fringed-micelles a morphology consist ing of loosely packed ethylene sequences is obtained. Although the granular structures, present in the very-low-density copolymers, are too small and/ or too imperfect to be detected by WAXD, the crystallisation and melting pr ocesses could still be readily measured by DSC and SAXS. Real-time SAXS measurements during a scan-iso temperature-time heating prog ram, as used in some temperature-modulated DSC (TMDSC) measurements, shows that in a homogeneous ethylene-l-butene copolymer (6.4 mole% l-butene) cons iderable instantaneous structural changes occur during dynamic (heating) an d static (isothermal) measurements, as is, for instance, reflected in the s ignificant increase of the SAXS invariant during the short isothermal stays . (C) 2000 Elsevier Science Ltd. All rights reserved.