Characterization of Ethylene/α-Olefin Copolymers Using High-Temperature Thermal Gradient Interaction Chromatography

Several crystallization-based techniques are used to measure the chemical-composition distribution of polyolefins, but they are limited to semicrystalline polyolefins. Recently, high-temperature thermal gradient interaction chromatography (HT-TGIC) has been developed to quantify the chemical-composition distribution of semicrystalline and amorphous polyolefins, thus broadening the range of techniques available for the analysis of polyolefin chemical-composition distribution. In HT-TGIC, the fractionation mechanism relies on the interaction of polyolefin chains with a graphite surface upon temperature change in an isocratic solvent. In the present investigation, a series of ethylene/1-octene copolymers having approximately the same molecular weight average and different comonomer fractions (up to 25% of 1-octene) is synthesized using a metallocene catalyst to investigate the fractionation mechanism of HT-TGIC. Three copolymer samples and their blends are also studied to determine which operation parameters influence the HT-TGIC peak shape and position. The cooling rate has no significant effect on the desorption temperature and the broadness of the HT-TGIC chromatograms. On the other hand, the heating rate and the elution flow rate substantially influence the peak temperature and breadth.