Development of Comprehensive Two-Dimensional High Temperature Liquid Chromatography × Gel Permeation Chromatography for Characterization of Polyolefins

This work documents the development of the title system wherein the first dimension is a separation of polyolefins, according to composition, via an adsorption mechanism on a HYPERCARB stationary phase, and the second dimension is a separation of polyolefins on a gel permeation chromatography (GPC) column. Proper optimization of the experimental parameters including high temperature liquid chromatography (HTLC) flow rate, GPC flow rate, GPC column type, and solvent gradient program enabled successful operation of the two-dimensional (2D) system. Two angle light scattering at 90° and 15° and solution infrared absorbance detectors were used for qualitative and quantitative analysis of the 2D data. Apparent composition distribution, apparent molecular weight distribution, and the complete two-dimensional (composition × molecular weight) distribution were obtained for a given polymer. This system is an improvement over a prior two-dimensional system based on temperature rising elution fractionation (TREF)/GPC in that TREF has difficulty separating polyolefins by composition if the polyolefins contain more than approximately 8 mol percent comonomer. Polyolefins synthesized from different catalysts (Metallocene and Ziegler−Natta) showed differences in the molecular weight, composition and number of resolved species in their respective 2D HTLC−GPC chromatograms as a function of catalyst type. Although the polymers studied here were all polyolefins, this approach can also be extended to other polymers.