For the first time, thermal field-flow fractionation (ThFFF) has been used for the separation of poly(methyl methacrylate) (PMMA) with regard to molecular microstructure. PMMA exists in three different isomeric forms, namely, isotactic, syndiotactic, and atactic. ThFFF analysis of the different PMMA isomers in tetrahydrofuran, acetonitrile (ACN), and dioxane reveals that isomers with similar molecular weights exhibit different Soret coefficients, and thus different retention times, under identical experimental conditions. Of the three solvents, ACN shows the greatest influence on fractionation of the isomers. The separation according to molecular microstructure is found to be based on the cooperative effects of the normal and thermal diffusion coefficients. Furthermore, it is found that blends of different PMMA isomers with similar molecular weights can be fractionated into their respective isomeric components. The distribution of the isomeric content in an atactic PMMA sample is determined quantitatively by fractionating the sample with ThFFF and subsequently analyzing the fractions 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.
Thermal field‐flow fractionation (ThFFF) is a powerful alternative to commonly used column‐based techniques to characterize star polymers according to their solution behavior, as well as different molecular parameters, such as size and composition. This study demonstrates, for the first time, that ThFFF is an effective tool to investigate the thermoresponsive nature of polymers. ThFFF analysis of linear and star polystyrene in THF, dimethylacetamide, and cyclohexane shows that star polymers are more temperature‐sensitive than their linear analogs regarding their sizes in solution. This temperature sensitivity influences the retention behavior in ThFFF. Moreover, it is demonstrated that the thermodynamic quality of the solvent significantly influences both the thermal diffusion coefficient and the temperature‐sensitive nature of the samples. Finally, changing the thermodynamic quality of the solvent causes deviations in determining the number of chain ends from ThFFF data.
Block copolymer micelles have attracted much attention as a versatile platform that can readily be adapted to a wide range of applications including drug delivery and the production of nanoscale patterns. However, current analytical techniques are not suitable to provide comprehensive information regarding size, molar mass, chemical composition, and micelle stability in different environments. It is shown by the analysis of polybutadiene−polystyrene micelles with various corona compositions that, in contrast to current techniques, multidetector thermal field-flow fractionation (ThFFF) is capable of separating micelles according to corona composition and providing comprehensive information on important micelle characteristics such as size, molar mass, chemical composition, and their respective distributions from a single analysis. Moreover, it is shown that ThFFF is a suitable technique to monitor the dynamics of mixed micelle formation in terms of size, molar mass, and chemical composition.
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.
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