Quantitative Assessment of 2D-LC Analysis of Polyolefins for Multiway Applications: Calibration of the Log M Axis

Two-dimensional high performance liquid chromatography (2D-LC) offers unique insights into the polyolefins’ chemical composition and how that relates to their molar mass distribution. Moreover, the numerical format of the sample’s 2D-LC data (i.e., the J x K matrix of molar mass (MM) and comonomer (CM) content, respectively) allows for further correlations between the sample’s structural parameters and its physical properties via statistical multi-way methods. However, before applying these advanced methods to multi-sample data sets, we first determined the extent of variability and quantitation limits of these structural parameters for individual samples. In this current work we evaluated the 2D-LC MM data (measured on one SEC column) for a number of metallocene-catalyzed polyethylene resins and compared the results to those acquired on a typical three column SEC unit. Our initial assessment shows that the presence of 1-decanol interferes with accurate MM measurements when using typical calibration methods that employ MHS constants. However, accurate MM data were obtained by using a single sample integral calibration (SSIC) method, where the sample’s MMD measured on a three-column SEC unit is used to calibrate the 2D-LC SEC data. The resulting MM values were within the expected error and consistent with published data. Additionally, the resulting MMD profiles, coupled with the known short-chain branching content for the samples, gave the expected crystallinity properties as measured by DSC and estimated densities.