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

Abstract

Several crystallization-based techniques are used to measure the chemical-composition distribution of polyolefi ns, but they are limited to semicrystalline polyolefi ns. Recently, high-temperature thermal gradient interaction chromatography (HT-TGIC) has been developed to quantify the chemical-composition distribution of semicrystalline and amorphous polyolefi ns, thus broadening the range of techniques available for the analysis of polyolefi n chemical-composition distribution. In HT-TGIC, the fractionation mechanism relies on the interaction of polyolefi n 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 infl uence the HT-TGIC peak shape and position. The cooling rate has no signifi cant effect on the desorption temperature and the broadness of the HT-TGIC chromatograms. On the other hand, the heating rate and the elution fl ow rate substantially infl uence the peak temperature and breadth. crystallization elution fractionation (CEF) [11][12][13][14] are crystallization-based techniques used extensively to measure the chemical-composition distribution (CCD) of polyolefi ns. In these techniques, chains with higher α-olefi n fractions crystallize at lower temperatures than chains with lower comonomer content. Differences in crystallizability are then expressed as differences in comonomer content using a calibration curve. The fractionation takes place by slowly decreasing the temperature of a dilute polymer solution, either in a stirred vessel (CRYSTAF) or in a packed column (TREF and CEF). However, these techniques are limited to semicrystalline polyolefi ns and may be affected by co-crystallization effects that reduce their resolution.High-temperature solvent gradient interaction chromatography (HT-SGIC) [ 15,16 ] has been used to fractionate polyolefi ns via an adsorption-desorption mechanism in porous graphitic carbon supports. The polyolefi n sample is adsorbed on a porous graphite column at 160 °C, and the retained polymer chains are then desorbed and eluted from the column using a solvent gradient. [17][18][19][20][21] HT-SGIC Macromol. Chem. Phys. 2014, 215, 465−475

Chemical Composition Fractionation of Olefin Plastomers/Elastomers by Solvent and Thermal Gradient Interaction Chromatography

“…For EP rubbers as well as for PP‐EPR reactor blends, TGIC remains insensitive for some compositions even if improved experimental protocols are applied. It will be interesting to see if a change in mobile phase broadens the accessible ethylene content range . This will be the subject of forthcoming investigations and will be of significant interest due to the fact that all industrially relevant EP rubbers have comonomer contents below 60 mol% ethylene.…”

“…As an alternative, thermal gradient interaction chromatography (TGIC) has been introduced where a single solvent is used as mobile phase enabling the usage of various detectors such as infrared (IR), light scattering (LS), and online viscometer . This method has been used extensively for the chemical composition analysis of LLDPE . While SGIC operates at temperatures above melting, and thus, sample crystallinity does not influence the fractionation process, TGIC uses a temperature gradient starting at ambient temperature.…”

“…While SGIC operates at temperatures above melting, and thus, sample crystallinity does not influence the fractionation process, TGIC uses a temperature gradient starting at ambient temperature. At this temperature, most sample components have crystallized or precipitated onto the stationary phase, and a mixed fractionation mechanism may take place in the elution process during the heating ramp . To determine the application ranges for both methods, it would have been necessary to fractionate the same sample set by SGIC and TGIC, which has never been done and it is addressed in this study.…”

Molecular Dynamics Simulation of Ethylene/Hexene Copolymer Adsorption onto Graphene: New Insight into Thermal Gradient Interaction Chromatography

“…Increasing heating rate leads to higher elution temperature (the temperature of the column will rise faster between the moment the polymer is desorbed and the moment it reaches the detector). Decreasing the elution rate results in higher elution temperature and broaden the TGIC profile probably due to an increased residence time in the column …”

“…Decreasing the elution rate results in higher elution temperature and broaden the TGIC profile probably due to an increased residence time in the column. [34][35][36] One of the key features of the TGIC profile is the broadening of the peaks at high α-olefins content. A similar feature was observed with TREF and it was attributed to the Stockmayer bivariate distribution of the copolymer chemical composition.…”