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

摘要

The thermal behaviour and morphology of series of homogeneous ethylene-propylene and ethylene-1-butene copolymers, which cover wide ranges in comonomer content, are studied by differential scanning calorimetry (DSC),time-resolved small-angle X-ray scattering (SAXS),wide-angle X-ray diffraction (WAXD)and transmission electron microscopy (TEM).The thermal behaviour and the 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 morpholgy into a granular one consisting of small block-shaped structures. When the comonomer amount is raised further to very high contents, possibly via fringed-micelles a morphology consisting 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 processes could still be readily measured by DSC and SAXS.Real-time SAXS measurements during a scan-iso temperature-time heating program, as used in some temperature-modulated DSC(TMDSC) measurements,shows that in a homogeneous ethylene-1-butene copolymer (6.4mole%1-butene) considerable instantaneous structural changes occur during dynamic (heating)and static (isothermal) measurements, as is, for instance, reflected in the signficant increase of the SAXS invariant during the short isothermal stays.