Transmission electron microscopy analysis of multiblock ethylene/1-octene copolymers

Abstract The crystalline morphology of ethylene/1-octene (EO-BC) statistical multiblock copolymers is investigated by transmission electron microscopy (TEM). EO-BCs are an important class of thermoplastic elastomers characterized by alternating crystalline, octene-poor, hard blocks and amorphous, octene-rich, soft blocks and statistical distribution of block length (BL) and number of blocks/chain (NB). Adopting similar crystallization conditions, samples with only subtle differences in the chain microstructure, are shown to display different solid-state morphology as probed by TEM and different melt rheology. In particular, the homogeneous or heterogeneous lamellar morphology which develops in the solid state reflects the tendency of the samples to show homogeneous or heterogeneous melt-rheology, respectively. As EO-BCs are a reactor blend of non-uniform chains, it is argued that the solid state and melt phase behavior of EO-BCs is controlled by differences in the relative abundance of chains including a prevalence of hard blocks of short and/or high length.