Multidimensional high-temperature liquid chromatography: A new technique to characterize the chemical heterogeneity of Ziegler-Natta-based bimodal HDPE

Abstract

High temperature two-dimensional liquid chromatography (HT 2D-LC) was recently introduced as a new technique to analyze the heterogeneities with regard to composition and molar mass present in model blends of polyolefins and various olefin copolymers. The method uses graphite as stationary phase and solvent gradients of 1-decanol → 1,2,4-trichlorobenzene as mobile phase for the compositional separation. With the aim to maximize the chromatographic resolution, the influence of the separation's temperature in the first dimension was evaluated: approaching the θ-temperature of polyethylene (PE) in 1-decanol selectively enhances the retention of higher molar mass PE standards while that of the lower molar mass ones is hardly affected. A bimodal ethylene/1-butene copolymer and its temperature rising elution fraction (TREF) fractions were separated by HT 2D-LC. For the first time, both axes of the contour plot were calibrated with regard to chemical composition and molar mass, respectively. Prefractionation of the bulk sample by TREF enhances the detectability of separated components of the 2D separation. The influence of the separation temperature, that is, working around the θ-temperature of PE in 1-decanol, can be used to enhance the chromatographic resolution of the 2D chromatography. © 2012 Wiley Periodicals, Inc.