Industrial polybutadienes synthesized by Ziegler–Natta catalysts may exhibit very high molar masses, significant degrees of branching, and gel species. Such samples were analyzed by size exclusion chromatography (SEC) and asymmetric flow field-flow fractionation (AF4). Both fractionation techniques were coupled to a multiangle laser light scattering (MALLS) detector as well as a refractive index (RI) detector. The initial results obtained from SEC measurements completely contradicted the processing behavior of the materials. SEC seemed not to be suitable for accurate characterization of these materials. SEC separation was strongly influenced by coelution of linear (low molar mass) and branched (high molar mass) macromolecules, shear degradation of the larger macromolecules, and filtration of the gel fraction. For this reason the polybutadienes were subsequently analyzed by AF4 in order to compare the results and identify the limitations of SEC. The results showed that, as a specialized tool, AF4 can be used for the extended and more accurate analysis of synthetic rubber materials, especially in the case of very high molar masses. SEC is not suitable for such samples because it does not properly address the high molar mass fraction and the branched macromolecules.

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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 the present investigation, styrene‐acrylic and pure acrylic emulsions used in water‐based decorative coatings are characterized by size exclusion chromatography (SEC) and asymmetric flow field‐flow fractionation (AF4). Both the separation techniques are coupled online to multiangle laser light scattering (MALLS) and refractive index detection to investigate the molar mass properties during the course of the free radical polymerization reaction. For the acrylic emulsion, kinetic samples are taken from the reactor at fixed time intervals and analyzed. In SEC‐MALLS, unusual elution behavior is observed which is found previously for highly branched polymer species. In contrast, the AF4 fractograms indicate normal mode elution without any unusual behavior as compared to the SEC analyses. The molar masses obtained by AF4 are significantly higher compared to the SEC results. Further, AF4 is used to determine the gel contents of the kinetic samples of the acrylic emulsion and for both the acrylic and styrene‐acrylic emulsions, AF4 proves to be a robust and feasible tool allowing for improved correlations of the molecular and materials properties of water‐based polymer emulsions.