Polyolefin Characterization by High Temperature Solvent Gradient Interaction Chromatography: Transitioning Away from Chlorinated Desorption Promoting Solvents

Abstract

Abstract High temperature solvent gradient interaction chromatography (HT-SGIC) has been established as a cornerstone technique to elucidate the chemical composition (CC) and underlying chemical composition distribution (CCD). In HT-SGIC, the adsorption (adsorlis) and desorption (desorlis) promoting solvents play an integral role in identifying these molecular characteristics. However, until now only a few select chlorinated solvents have been used as desorlis for polyolefin separation in spite of their health and safety considerations. Towards the goal of identifying non-chlorinated desorlis, a recent approach integrating Structure Retention Relationship (SRR) with Relative Energy Density (RED) for identifying new desorlis was employed. The effectiveness of the SRR-RED plot as a tool for classifying solvents into adsorlis and desorlis in HT-SGIC of polyolefins was investigated. Non-chlorinated desorlis identified through this method were assessed using polyethylene samples of different molar mass (MM) followed by testing on polypropylene of different tacticity. Furthermore, ethylene propylene (EP) copolymers covering a wide range of CC were employed. At the same time, correlations between the retention factor of the desorli (from SRR study) and parameters such as MM, comonomer content and elution volume were studied to examine the desorption strength of the desorlis. The non-chlorinated desorlis were further used to separate linear low-density polyethylene and ethylene propylene diene copolymers to evaluate their potential across a broad range of polyolefins. Overall, non-chlorinated desorlis 1,2,4-TMB and tetralin were realized as alternative candidates to replace chlorinated solvents for polyethylene with moderate molar mass and EP copolymers higher comonomer content. Two strategies to increase the effective retention factor of the non-chlorinated desorlis by adding a strong-retention component were assessed based on their measured retention factors but their effect on the desorption behavior of polyolefins remains to be validated.