Heterophasic ethylene-propylene copolymers: New insights on complex microstructure by combined molar mass fractionation and high temperature liquid chromatography

The present study investigates the changes in the microstructure of heterophasic ethylene propylene copolymers (HEPCs) with increasing ethylene content, before and after visbreaking. Three samples obtained from commercial gas process reactors at Sasol Polymers at varying times after the addition of the ethylene comonomer are further visbroken to produce three more samples. Bulk sample analyses indicate that the ethylene-rich rubber phase which is essential in aiding peroxide mobility during visbreaking as observed in narrower dispersities and lower peak molar masses with increasing ethylene content. Further investigations of the microstructure via offline coupling of preparative molar mass fractionation (pMMF) to advanced analytical techniques such as solvent gradient interaction chromatography (SGIC) reveal that ethylene-rich copolymer chains are not significantly affected by the peroxide as the polypropylene homopolymer. Consequently, the polypropylene (PP) homopolymer and polypropylene-rich fractions with high molar mass diminish after visbreaking. Furthermore, the increase in ethylene content was observed to reduce the impact of the peroxide on the fraction quantities before and after visbreaking implying that visbreaking affects more the polyolefin chains with more PP segments and less those with more ethylene comonomer. •High temperature interaction chromatography is used to separate components of heterophasic ethylene-propylene copolymers.•Two-dimensional liquid chromatography is used to track the changes in the alloy components before and after visbreaking.•There is evidence that the rubber phase may promote mobility of peroxide in the polypropylene matrix during degradation.•Fractionation and analysis of fractions confirms peroxide impact on polypropylene rather than ethylene-rich components.