Determination of Molecular Weight Distribution of Polymers by Thermal Field-Flow Fractionation

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Abstract
The Thermal Field-Flow Fractionation method was used to determine average molecular weights for standard polystyrene samples with narrow distribution whose molecular weight ranged from 3600 to 867000. An effective calibration method was proposed and verified, and through the use of this method experimental fractograms could be interpreted in terms of sample molecular weight. Results were obtained by measuring at three temperature differentials (ΔT = 10°, 15°, and 40°C). The average molecular weights calculated from the fractograms were in very good agreement with the data given for these polystyrene standards by the supplier, and with the results calculated from size exclusion chromatography data. Polydispersity indices were calculated from the fractograms without corrections for longitudinal zone broadening. In view of the potential experimental errors associated with any measurement of polydispersity such corrections do not appear necessary for proper evaluation of data collected even in channels of standard efficiency. A substantial increase in efficiency can be reached e.g., by reducing the thickness of the channel by a factor of two. Results presented in this paper confirm the prospects offered by the Field-Flow Fractionation method for determinations of molecular weights, and eventually also molecular weight distributions for polymers. The method used to analyze the experimental results indicates that the Field-Flow Fractionation technique may be used as a standard high efficiency method for characterizing polymers.