Abstracts Chemistry

Development of Novel Methodologies to Characterize Polyolefinsusing Multi-dimensional High Temperature Liquid Chromatography

by Nagar Prabhu Kavimani

Developments in polyolefin catalysis during the last 50 years made it possible to synthesize polymer with a vastly improved control of regio- and stereo-selectivity, branching (their number and length) and the order, in which the monomers are incorporated into a polymer chain. At the same time, this created the need to develop appropriate and more comprehensive analytical methodologies for their molecular characterization. The molecular heterogeneities in polyolefins can to a large extent be defined by the molecular mass distribution (MMD), chemical composition distribution (CCD) and stereo-regularity distribution (SRD). Recently, HT-HPLC in the form of High Temperature Solvent Gradient Interaction Chromatography (HT-SGIC) has become an emerging technique to determine the CCD of polyolefins. The interrelationship between the distributions with regard to composition and molar mass can be studied by hyphenating HT-LAC and HT-SEC. The aim of the work presented in this thesis was to develop improved quantitative methodologies to separate complex polymer, which are broadly distributed with regard to both composition and molar mass using HT 2D-LC. The research presented in this thesis is divided into four parts. Upon giving a concise synopsis on the state of the art and the results, the conclusions will be summarized for each part separately. In the first part a methodology was developed to separate bimodal high density polyethylene (BiHDPE) (non-polar polyolefins) into its constituents, HDPE and LLDPE, by using HT-SGIC. A stepwise optimization of the HT-HPLC chromatographic parameters, comprising gradient slope and temperature was carried out using model homo- and copolymers of ethylene. The goal was to minimize the impact of the molar mass on the composition separation. Then separation achieved by the developed HT-HPLC was further optimized via hyphenation with HT-SEC. The effects of column temperature, the volume of the HT-HPLC fractions injected into the HT-SEC and the separation efficiency of the HT-SEC were investigated. Bimodality was observed for the first time in both HT-HPLC and HT-SEC dimension for BiHDPE in HT 2D-LC. This was achieved by using a low transfer volume of 100 μL, a HT-SEC column with high theoretical plate number (N11000) and by providing sufficient time for one HT-SEC analysis. To achieve quantitative information the evaporative light scattering detector (ELSD) was replaced by an infrared (IR) detector and BiHDPE was analyzed by HT 2D-LC. Yet, to fully use the potential of IR detection for HT 2D-LC in the case of BiHDPE several chromatographic parameters had to be carefully optimized. With each fraction transfer from the HT-HPLC into the HT-SEC dimension in HT 2D-LC, a small amount of 1-decanol (solvent plug) is injected, with the amount depending on the gradient. Since the IR detector used here is tuned to the stretching vibration of the methyl and methylene groups, 1-decanol causes an intense broad peak in the chromatograms which may significantly overlap with the polymer peak when a column of… Advisors/Committee Members: Matthias, Rehahn (advisor), Markus, Busch (advisor), Barbara, Albert (advisor), Rolf, Schaefer (advisor).