Advanced fractionation methods for the microstructure analysis of complex polymers

Abstract

This review discusses some recent work on the microstructure analysis of complex polymers using advanced fractionation methods. Complex polymers are distributed in a number of molecular parameters including molar mass, chemical composition, molecular architecture, and microstructure. Molar mass and chemical composition analysis is typically conducted by a range of spectroscopic and chromatographic methods, size exclusion chromatography and high-performance liquid chromatography (HPLC) being the most important fractionation methods. It is shown that HPLC is also very sensitive regarding polymer microstructure and can be used for the fractionation of e.g. polymethacrylates, polyisoprene, and polybutadiene. The best approach to the quantitative analysis of microstructure distributions is the on-line coupling of the fractionation with 1 H nuclear magnetic resonance spectroscopy. The spectroscopic analysis of chromatographic fractions provides concentration profiles of the tactic units as a function of the chromatographic separation and can be used for both HPLC and size exclusion chromatography. Apart from column-based fractionations, channel-based fractionations such as thermal field flow fractionation are powerful tools for microstructure analysis of complex polymers. It has been shown very recently that thermal field flow fractionation is capable of fractionating polyisoprene and polybutadiene according to microstructure.

Deformulation of commercial linear low‐density polyethylene resins by advanced fractionation and analysis

“…The MMD of polyolefins is typically analyzed using high‐temperature SEC (HT‐SEC) . This is not necessarily the case for commercial materials that are rather characterized by parameters such as the melt flow index.…”

“…For the analysis of the chemical composition of polyolefins, the use of NMR and Fourier transform infrared (FTIR) spectroscopies as quick analytical tools is a common approach, although these methods only provide average numbers . Other powerful analytical techniques include crystallization‐based techniques such as DSC, crystallization analysis fractionation, crystallization elution fractionation and solution crystallization by laser light scattering . These techniques, however, cannot be used for non‐crystallizing (amorphous) components.…”

Comprehensive branching analysis of polyethylene by combined fractionation and thermal analysis

“…Typically, the MMD of polyolefins is analysed by high‐temperature size exclusion chromatography (HT‐SEC) . For linear copolymers, the hydrodynamic size is a function of molar mass and chemical composition while for branched homopolymers such as LDPE the hydrodynamic size depends on molar mass as well as the number and the length of the branches.…”

“…High‐temperature high performance liquid chromatography (HT‐HPLC) is able to fractionate polyolefins according to their chemical composition or branching irrespective of crystallizability. Accordingly, this technique is a selective fractionation technique for both crystalline and non‐crystalline materials …”

A Monte Carlo study on LCCC characterization of graft copolymers at the critical condition of side chains

“…However, SEC cannot effectively separate graft copolymers that have both molecular weight and chain architecture distributions [8,9]. In recent years, some new liquid chromatographic methods other than SEC, such as liquid chromatography at the critical condition (LCCC) [8,10,11] and liquid adsorption chromatography (LAC) [8], have been developed for the characterization of complex polymers according to their chain architecture and/or chemical composition. LCCC has been shown to be a very effective method to characterize individual blocks in linear block copolymers [12e14] as well as graft copolymers [11,15,16].…”