Selective TREF Fraction Removal: A Method to Enhance Crystallinity and Microhardness in Propylene–1-Pentene Copolymers

Abstract

Innovative advancements in polyolefin chemistries are critically important to develop industrial applications that require an ability of either superior performance levels or minimal expense. While temperature rising elution fractionation (TREF) is a well-established analytical technique for characterising polyolefin heterogeneity, its use as a preparative tool for actively engineering properties remains underexplored. This research investigated the effects of continual extraction of fractions of copolymers, through either molecular fractioning or selective fractions, for propylene–1-pentene copolymers, on structure–property relationships. Moving beyond the established correlation between elution temperature and comonomer content, this study demonstrates how the strategic subtraction of amorphous-rich or crystalline-rich fractions can systematically tune the bulk material’s properties. Conditions were created to allow for systematic removal of selected fractions while characterising the remaining polymer by density-based fractional crystallinity, differential scanning calorimetry (DSC), ¹³C NMR, micro-hardness testing and positron annihilation lifetime spectroscopy (PALS). This study has demonstrated the potential to directly enhance the crystallinity and microhardness of the copolymer by selectively removing amorphous-rich fractions. More importantly, it establishes ‘selective fraction removal’ as a proof-of-concept for a new materials design strategy. In contrast, it is not very likely that removing fractions of highly crystalline-based polymer will create improvements to properties. In addition, this study has shown that selectable fractions provide an effective means to tune polymer properties at the laboratory scale. While the method demonstrates potential, its industrial scalability would require further research and methodological adaptation.