Characterization of broad molecular weight distribution polyethylene with multi-detection gel permeation chromatography

Abstract

High temperature gel permeation chromatography (GPC) equipped with differential refractive index, light scattering and viscometer is used to characterize polyethylene with broad molecular weight distribution (MWD). Methods are discussed through the measurement of broad MWD polyethylene PE52K and 4731B, including Mark-Houwink calibration, universal calibration, triple-detectors and light scattering dual-detectors calibrations. As the broadness of MWD increases, the two fitting curve calibrations with first order equations are chosen, despite a slight inaccuracy within molecular weight range of standards. More reliable polymer dispersity indexes (PDI) are obtained by triple-detectors and light scattering dual-detectors calibrations. From the Mark-Houwink plot of 4731B, branching information can only be obtained from triple-detectors calibration, indicating the validity of triple-detectors calibration on the characterization of branched polyethylene with broad MWD. The triple detectors calibration upon 4731B provides a weight average molecular weight of 313 kg/mol, a PDI of 47 and a branching of 0.30 per chain.