Recent advances in high-temperature fractionation of polyolefins

The synthesis and characterization of polyolefins continues to be one of the most important areas for academic and industrial research. One consequence of the development of new “tailor-made” polyolefins is the need for new and improved analytical techniques for the analysis of polyolefins with respect to molar mass, molecular topology and chemical composition distribution. This review presents different new and relevant techniques for polyolefin analysis. The analysis of copolymers by combining high-temperature SEC and FTIR spectroscopy yields information on chemical composition and molecular topology as a function of molar mass. Crystallization based fractionation techniques are powerful methods for the analysis of short-chain branching in LLDPE and the analysis of polyolefin blends. These methods include temperature-rising elution fractionation, crystallization analysis fractionation and the recently developed crystallization-elution fractionation. The latest development in the field of polyolefin fractionation is high-temperature interaction chromatography. Based on the principles of gradient HPLC and liquid chromatography at critical conditions this method is used for fast analysis of the chemical composition distribution of complex olefin copolymers. The efficiency of HPLC based systems for the separation of various olefin copolymers will be discussed. The ultimate development in high-temperature fractionation of polyolefins is comprehensive high-temperature two-dimensional liquid chromatography. The review will discuss some of the pioneering work that has been done since 2008. Finally, the correlation between molar mass and chemical composition can be accessed by on-line coupling of high-temperature SEC and 1H-NMR spectroscopy. It is shown that the on-line NMR analysis of chromatographic fractions from high-temperature fractionations is possible and yields information on microstructure and tacticity in addition to molar mass and copolymer composition