Joint Effect of Poly(ethyhlene-co-1-octene) Chain Length and 1-Octene Fraction on High-Temperature Thermal Gradient Interaction Chromatography

High-temperature thermal gradient interaction chromatography (HT-TGIC) fractionates polyolefins based on an adsorption-desorption mechanism. Several factors influence the shape and position of HT-TGIC chromatograms, notably polymer microstructure, analytical conditions, and, to a lesser extent, solvent type. This article investigates the joint influence of chain length and comonomer content of a series of polyethylene and ethylene/1-octene copolymers having similar 1-octene fractions (0-13 mol%) and a wide range of molecular weights on HT-TGIC fractionation. For each series of copolymers having similar 1-octene fraction, the elution peak temperature decreases exponentially and the profiles become increasingly broader below a critical number average chain length value. The authors use Monte Carlo simulation and Stockmayer distribution to explain the observed behavior, finding that no simple correlation exists between ethylene sequences in the copolymers and peak elution temperature, but that there is strong evidence that axial dispersion is responsible for symmetrical broadening of the HT-TGIC profiles. The authors also study the HT-TGIC of binary blends, finding that components with similar 1-octene contents and dissimilar chain lengths tend to increase co-adsorption/co-desorption effects.