Lars-Christian Heinz

High-Temperature Liquid Chromatography at Critical Conditions: Separation of Polystyrene from Blends with Polyethylene and Ethylene-Styrene Block Copolymers

ABSTRACT Liquid chromatography at critical conditions (LCCC) is an important tool for the separation of complex polymers according to chemical composition. For ambient temperatures more than 150 different LCCC separation systems are known, while at temperatures that are suitable for chromatography of polyolefins (i.e. > 130°C) not a single system is known from literature. In this article we present LCCC conditions for polystyrene at a temperature of 140°C and their application to the analysis of polymer blends composed of polystyrene and polyethylene or styrene-ethylene block copolymers.

Development of high-temperature separation techniques for the chemical composition analysis of ethylene - methyl methacrylate block copolymers

Abstract Ethylene - methyl methacrylate block copolymers are semicrystalline polymers that dissolve in organic solvents only at high temperatures. Accordingly, microstructure analysis by solution methods must be conducted at temperatures above 130°C. For the analysis of block copolymers of different compositions several analytical techniques were used, including high-temperature size-exclusion chromatography (SEC), hyphenated SEC-FTIR, and CRYSTAF (crystallisation analysis fractionation). While SEC with refractive index detection indicated a certain multimodality of the samples, SEC coupled with FTIR revealed that the samples were chemically inhomogeneous and may contain homo- and copolymer fractions. The presence of polyethylene and poly(methyl methacrylate) homopolymers in the copolymer samples was confirmed by CRYSTAF analysis, when the total concentration as well as the carbonyl group distribution were monitored separately. Chromatographic separation of the different sample components was achieved when liquid chromatography at critical conditions (LC-CC) was used. For the first time, true high-temperature LC-CC methods were developed operating at a column temperature of 140°C. As the stationary phase, silica gel was used. Suitable mobile phases were binary mixtures of 1,2,4-trichlorobenzene or 1,2- dichlorobenzene with cyclohexanone. Using LC-CC, the samples were separated into the copolymer and the homopolymer fractions.

Two-dimensional chromatography of complex polymers, 5 Separation of blends of styrene-butadiene rubber and butyl rubber

Abstract Separation of blends of styrene-butadiene rubber and butyl rubber was accomplished by gradient HPLC. Using a polar stationary phase and chloroformcyclohexane as eluent, the blends were separated with regard to chemical composition, irrespective of the molar masses of the components. The exact chemical structure of the blend components was analysed by coupling the chromatographic separation to FTIR detection. FTIR spectra of the components reveal information on styrene and butadiene contents and the conformation of the butadiene units (1,2-, 1,4-cis and 1,4-trans units). Complete separation of the blends with respect to chemical composition and molar mass was achieved by two-dimensional liquid chromatography. Combining gradient HPLC and size exclusion chromatography in a fully automated 2D chromatography set-up, the complex distributions of chemical composition and molar mass were fingerprinted simultaneously.