Multidetector Thermal Field‐Flow Fractionation as a Novel Tool for the Microstructure Separation of Polyisoprene and Polybutadiene

Abstract

For the first time, it is demonstrated that thermal field-flow fractionation (ThFFF) is an efficient tool for the fractionation of polyisoprene (PI) and polybutadiene (PB) with regard to molecular microstructure. ThFFF analysis of 1,4- and 3,4-PI as well as 1,4- and 1,2-PB samples in tetrahydrofuran (THF), THF/cyclohexane, and cyclohexane reveals that isomers of the same polymer family having similar molar masses exhibit different Soret coefficients depending on microstructure for each solvent. The separation according to microstructure is found to be based on the cooperative influence of the normal and the thermal diffusion coefficient. Of the three solvents, cyclohexane has the greatest influence on the fractionation of the isomers. In order to determine the distribution of isomeric structures in the PI and PB samples, the samples are fractionated by ThFFF in cyclohexane and subsequently analyzed by (1) H NMR. The isomeric distributions determined from NMR data correlate well with ThFFF retention data of the samples and thus further highlight the unique fractionating capabilities of ThFFF. The interplay of the normal and thermal diffusion coefficients that are influenced by temperature and the mobile phase opens the way to highly selective fractionations without the drawbacks of column-based separation methods.

Tacticity Separation of Poly(methyl methacrylate) by Multidetector Thermal Field-Flow Fractionation

“…An interesting preliminary result was obtained recently showing that polyisoprene and polybutadiene isomers can be fractionated according to microstructure. 12 Using a ThFFF setup coupled to multiangle laser light scattering (MALLS), differential refractive index (dRI), and dynamic light scattering (DLS) detectors, it was proven that the fractionation was based on differences solely in the polymer microstructure. Polyisoprene was fractionated into the 1,4-, 1,2-and 3,4-isomers, and polybutadiene was fractionated into the 1,4-and 1,2-isomers.…”

Advanced fractionation methods for the microstructure analysis of complex polymers

“…In a very recent study Greyling and Pasch demonstrated that, in addition to fractionation according to size and chemical composition, ThF3 is capable of fractionating PI and PB according to microstructure. [66] This work, for the first time, described the characterization and fractionation of PI and PB isomers according to microstructure by multidetector ThF3, which enabled the simultaneous on-line determination of the molar mass distributions by multiangle laser light scattering as well as the diffusion and thermal diffusion coefficients of the eluting polymers by dynamic light scattering. A differential refractometer was required as universal concentration detector.…”

“…Thermal diffusion, D T , drives polymers toward the accumulation wall, while diffusion, D , causes migration away from the wall. The Soret coefficient, S T , determines the position in velocity profile and elution from channel (reprinted from Greyling and Pasch with permission). This figure is available in colour online at wileyonlinelibrary.com/journal/pat…”

Characterisation of block copolymer self‐assemblies by thermal field‐flow fractionation

“…ThFFF is a sub‐technique of FFF that applies a temperature drop across an open, ribbon‐like channel in order to fractionate analytes according to size, chemical composition and microstructure . The first reported attempts to fully utilise the advantages and unique separation capabilities of ThFFF to separate micelles according to corona composition were performed on poly(methyl methacrylate)–polystyrene micelles in acetonitrile using a multidetector ThFFF setup as illustrated in Scheme .…”