Simplified Robust Triple Detection Methods for High Temperature GPC Analysis of Polyolefins

Abstract

Very powerful triple detector high‐temperature gel permeation chromatography (HT‐GPC) systems equipped with concentration, viscosity, and multiple angle light scattering detectors can be found in many polyolefin characterization laboratories. However, the complexity and sometimes lack of robustness of some detection methods often result in failure to achieve the required precision and long‐term reliability to properly support the industrial needs. Two methods for data processing in triple detector HT‐GPC of polyolefins are here described aiming at overcoming those difficulties, specifically those related to the application of multiple angle light scattering. In the first place, we propose here a data processing method using light scattering data collected at only one angle, with application of a dissymmetry correction based on an estimate of the molecular size from the hydrodynamic volume given by the universal calibration. This method (SALSDC: single‐angle light scattering with dissymmetry correction) is simple and robust for molar mass distribution and averages. Long chain branching detection and quantification is another field plagued with lack of precision and inconsistency problems, due to the difficulty in collecting reliable radius of gyration (Rg) data using MALS, for calculation of the g‐index. A novel approach to estimate the g‐index, based on point‐by‐point calculation of the gpcBR index is here described and evaluated.