Influence of Chain Microstructure on Liquid–Liquid Phase Structure and Crystallization of Dual Reactor Ziegler–Natta Made Impact Propylene–Ethylene Copolymers

The relationship between ethylene content, phase structure, crystallization behavior, and the inferred mechanical performance has been studied in five impact copolymers with overall ethylene content between 8 and 11 mol %. Thermal characterization data and crystallization kinetics of impact polypropylene copolymers (IPC) do not scale with content of ethylene. Emphasis is given to understand the correlation between heterophasic morphology assessed by scanning electron microscopy and polarized optical microscopy and the properties of the crystalline propylene–ethylene copolymer component extracted via fractionation. As the mass fraction of the rubber component is equivalent for all IPC, the scaling between ethylene content and increased droplet size is explained by the observed differences in dynamics of the crystalline ethylene–propylene copolymer molecules during the liquid–liquid phase separation step. On this basis, a correlation is inferred between cocrystallization and compatibility of the components that make the observed multiphase morphologies and the IPC mechanical behavior.