Solution and solid-state NMR characterization of heterophasic propylene–ethylene copolymers (HEPC) with increasing ethylene content

Abstract

Solid-state and solution 13C NMR were used as complementary techniques to investigate changes in the molecular dynamics and chemical composition of different semi-crystalline fractions obtained using temperature rising elution fractionation (TREF) from heterophasic ethylene/propylene copolymers (HEPCs). The HEPCs were selected during a transition from homopolymer to copolymer and represent a range of total ethylene contents between 2 and 12mol%. It was found that these techniques yielded complimentary information, further breaking down the complexity of these polymers and providing observations that have not yet been obtained for these polymers by other experimental techniques. Ethylene dependent changes in the methylene region of solid-state spectra obtained for the bulk HEPCs was observed. Solid-state analysis of the semi crystalline fractions of these polymers provided more insight on this observation as well as on the distribution of these components between fractions with different crystallinities. From the solution NMR results, the distribution of different ethylene sequences between the fractions was evaluated and a statistical model proposed for this evolution. Furthermore the development of longer ethylene sequences observed by solution NMR was found to correspond with an increase of ethylene within rigid areas in the higher temperature semi-crystalline fractions. Thus a clearer understanding was obtained of how the different semi-crystalline copolymers, responsible for phase interactions and ultimately final product properties, develop with increasing ethylene incorporation.