Field-flow fractionation (FFF) is a powerful alternative to column-based polymer fractionation methods such as size-exclusion chromatography (SEC) or interaction chromatography (IC). The most common polymer fractionation method, SEC, has its limitations when polymers with very high molar masses or complex structures must be analysed. Another limitation of all column-based methods is that the samples must be filtered before analysis and shear degradation of large macromolecules may be caused by the stationary phase and/or the column frits. Finally, the separation of very polar polymers may be a challenge because such polymers interact very strongly with the stationary phase, causing irreversible adsorption or other negative effects. This article reviews the latest developments in field-flow fractionation of complex polymers. It is demonstrated that some of the limitations of column-based chromatography can be overcome by FFF. When appropriate, results from column-based fractionations are compared with those from FFF fractionations to highlight the specific merits and challenges of each method. In addition to the fractionations themselves, various detector setups are discussed to show that different polymer distributions require different experimental procedures. Examples are given of the analysis of molar mass distribution, chemical composition, and microstructure. Advanced detector combinations are discussed, most prominently the very recently developed coupling to (1)H NMR. Finally, analysis of polymer nanocomposites by asymmetric flow field-flow fractionation (AF4)-FTIR is presented.

Asymmetrical flow field-flow fractionation (AF4) was used as a fractionation technique to investigate the molecular heterogeneity of poly(styrene-b-isoprene) diblock copolymers synthesized by either sequential living anionic polymerization or coupling of living precursor blocks. AF4 coupled to multi-angle laser light scattering (MALLS), refractive index (RI), and ultraviolet (UV) detectors was used to separate the diblock copolymers from the homopolymers and coupling products, and the molar masses of the different components were analyzed. In order to get more information about the separated block copolymers, homopolymers, and coupling products, fractions were collected directly after the AF4 channel. The collected fractions were analyzed offline by (1)H NMR to provide identification of the different species and additional information on the true chemical composition, and the microstructure of the diblock copolymer was obtained.

In this study, multidetector Thermal FFF (ThF3) is utilized to study amphiphilic block copolymers in different selective and nonselective solvents. Depending on the solvent quality and the polymer concentration, amphiphilic block copolymers can form aggregates or micelles; the blocks can adopt different coil conformations. ThF3 is chosen because of the noninvasive nature of the technique that will not destroy the conformations that amphiphilic block copolymers can adopt in selected solvents. The effect of different polymer-solvent systems on the diffusion and thermal diffusion coeffi cients, and the resultant separation, is studied. It is found that, depending on the solvent, the macromolecules adopt extended coil or partially collapsed coil conformations. Experimental conditions are identifi ed where the block copolymers behave similar to one of their parent homopolymers. For the fi rst time, it has been shown that ThF3 is a unique tool to study the solution properties and the coil conformations of amphiphilic copolymers and to relate this information to the fractionation behavior of the polymers. block copolymers have a tendency to aggregate and even form micelles under suitable conditions. Classical chromatographic techniques utilize packed columns to fractionate polymers. These packed columns contained microporous particles as stationary phase that can destroy given conformations or prevent aggregation or micelle formation. To study the behavior of amphiphilic block copolymers in different solvents, fi eld-fl ow fractionation (FFF), specifi cally thermal fi eld-fl ow fractionation (ThF3) was chosen. ThF3 utilizes an open channel that is conducive to the analysis of shear sensitive polymer structures. The mechanism of separation is not reliant on adsorption and thus sample loss is minimized. The separation force, a thermal gradient, is applied perpendicular to the eluent fl ow through the channel and the separation is governed by both diffusion and thermal diffusion. These two forces act in opposition to each other and allow separation according to molecular size and chemical composition.ThF3 and, more recently, microthermal field-flow fractionation are subtechniques of FFF that have been