Molecular composition field-flow fractionation

In conclusion one can say that SEC is a very powerful method for polymer characterization, especially in combination with other composition sensitive or absolute calibration methods. A big advantage is also that the sample amount is fairly small, typically 10 mg. For more complex polymers, such as polyelectrolytes, enthalpic effects often become dominant and also for rather high molecular weight polymers chromatographic methods such as field-flow fraction (FFF) techniques might be more suitable. For fast routine measurements linear columns are often used. 

Schimpf ME (1995) Determination of molecular weight and composition in copolymers using thermal field-flow fractionation combined with viscometry. In Provder T, Barth HG, Urban MW (eds) Chromatographic characterization of polymers hyphenated and multidimensional techniques. American Chemical Society, Washington, DC, pp 183-196... 

This book covers some of the significant advances in hyphenated chromatographic separation methods for polymer characterization. Chromatographic separation techniques in this volume include size-exclusion chromatography, liquid chromatography, and field flow fractionation methods that are used in conjunction with information-rich detectors such as molecular size-sensitive or compositional-sensitive detectors or coupled in cross-fractionation modes. 

Determination of Molecular Weight and Composition in Copolymers Using Thermal Field-Flow Fractionation Combined with Viscometry... 

X HERMAL FIELD-FLOW FRACTIONATION (ThFFF) separates polymers according to their molecular weight and chemical composition. The molecular weight dependence is well understood and is routinely used to characterize molecular weight distributions (1-4). However, the dependence of retention on composition is tied to differences in the thermal diffusion of polymers, which is poorly understood. As a result, the compositional selectivity of ThFFF has not realized its full potential. How-... 

Jeon, S.J. Schimpf, M.E. Cross-fractionation of copolymers using SEC and thermal field-flow fractionation for determination of molecular weight and composition. In Chromatography of Polymers Hyphenated and Midtidimensiorud Techniques, Provder, T., Ed. ACS Symposium Series No. 731, Ch ter 10 ACS Publications Washington, DC, 1999 141-161. 

Field flow techniques have been reviewed in a number of articles [148-150]. Sedimentation field flow fractionation has found use in the separation of PVC [151, 152], polystyrene [151-153], poly(methyl methacrylate) [153, 154], poly (vinyl toluene) [155] and poly(glycidyl methacrylate) latexes [156] to produce particle-size distributions and particle densities. It has also been applied in polymer-aggregation studies [157], pigment [157] quality control and in the separation of silica particles [158] and its performance has been compared with that of ultracentrifugation [159]. Thermal field flow fractionation has been used successfully in the characterisation of ultra-high-molecular-weight polystyrenes [160, 161], poly(methyl methacrylate), polyisoprene, polysulphane, polycarbonate, nitrocellulose, polybutadiene and polyolefins [162]. In the difficult area of water-soluble polymers, poly(ethylene glycol), poly(ethylene oxide), poly(vinyl pyrrolidone) and poly(styrene sulphonate) have been analysed [163, 164]. In addition, compositional separations have been achieved for polystyrene-poly(methyl methacrylate) mixes [165] and comparisons between TFFF and SEC have been made [166]. 

J. Giddings and K. Caldwell, Field-Flow Fractionation, B. W. Rossiter and J. F. Hamilton, eds.. Physical Methods of Chemistry, Vol. 3, Part B, Determination of Chemical Composition and Molecular Structure. Wiley-Interscience, New York, 1989. 

Experiments confirm the decrease in the ripening rate on addition of a poorly soluble component to the dispersed phase. Buscall et alP examined emulsions of SDS after adding long chain alkanes. Kabal nov et al showed that eqn. (1.22) was well obeyed for emulsions of SDS and hexane to which small quantities of the alkanes octane to hexadecane were added. Recently, Weers and Arlauskas have provided the first experimental evidence that molecular diffusion in two-component mixtures leads to an increase in the mole fraction of the less soluble component in the smaller drops. Using the technique of sedimentation field-flow fractionation coupled with gas chromatography, the disperse phase composition can be determined for monosized drop fractions. Evidence is also provided for the development of bimodal distributions at low volume fractions of the less soluble component, in excellent agreement with the above predictions. Their system was perfluorooctyl bromide (plus perfluorododecyl bromide) as oil stabilised by egg yolk phospho-lipid.2 ... 

The thermal field-flow fractionation (TFFF) was also coupled off-line with MALDI. This particular technique is especially able to separate large polymers according to their molecular masses, chemical composition, and microstructure. Routine MALDI-TOF MS analyses of PS polymers up to 575 kDa could be performed. 

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