Composition and molecular weight analysis of styrene-acrylic copolymers using thermal field-flow fractionation

2015

Anal. Chem.

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.

mentioning

confidence: 99%

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

2015

Anal. Chem.

“…Despite the remarkable separation capabilities of ThFFF only a few studies have addressed the characterization of star polymers by ThFFF. To date, it has been shown that ThFFF can be used to separate star and linear polymers based on differences in hydrodynamic size and that the chemical composition distributions as well as the number of arms of miktoarm star copolymers can be determined . On a fundamental level, it has been reported that D T is independent of either polymer size or the type of branching for polystyrene in ethylbenzene .…”

Section: Introductionmentioning

confidence: 88%

“…Another limitation of SEC is absorption of analyte molecules onto the stationary phase. Recently, open channel‐based techniques such as asymmetrical flow field‐flow fractionation (AF4) and thermal field‐flow fractionation (ThFFF) have successfully been used to characterize star polymers regarding different molecular parameters (such as size and molar mass) and were shown to have several significant advantages over column‐based techniques . These advantages include the absence of shear degradation, absorption onto a stationary phase, and well‐understood “normal” elution behavior.…”

Section: Introductionmentioning

confidence: 99%

Thermal Field‐Flow Fractionation for the Investigation of the Thermoresponsive Nature of Star and Linear Polystyrene

Lederer

Macro Chemistry & Physics

2018

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.

“…This migration under a thermal gradient is termed thermal diffusion and is characterized by the thermal diffusion coefficient, D T . Thermal diffusion is counteracted by ordinary diffusion, D, which is the migration of molecules away from the accumulation wall toward the center of the channel due to increasing analyte concentration at the accumulation wall (Figure S1, Supporting Information) …”

Section: Introductionmentioning

confidence: 99%

“…Laminar flow conditions within the channel result in a parabolic flow velocity profile across the channel with the fast flow streams toward the center of the channel and the slower streams near the channel walls . As with all FFF subtechniques, elution from the channel is determined by the analyte's average distance from the accumulation wall and thus their position in the velocity profile .…”

Section: Introductionmentioning

confidence: 99%

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

Macromol. Rapid Commun.

2014

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.