Extension of thermal field-flow fractionation to ultra-high (20 .times. 106) molecular weight polystyrenes

Abstract

The theory and practice of thermal field-flow fractionation (thermal FFF) as a tool for characterizing the molecular weight distribution of polymers are reviewed and a number of advantages with respect to size exclusion chromatography (SEC or GPC) are summarized. Retention values are measured and tabulated for linear polystyrenes in THF in the molecular weight range 5.1 X 104 to 20.6 X 106. For calibration purposes, it is shown that a plot of the logarithm of the product of retention parameter X and temperature drop AT vs. the logarithm of molecular weight is linear for this entire experimental range with a slope of -0.53. To demonstrate fractionation and the absence of shear degradation in the higher molecular weight range, a fraction was cut from the 20.6M peak, reinjected, and observed to elute as a narrow peak centered near the position of the cut. Calculations based on nonequilibrium theory show that column band broadening for a 20.6M peak eluted at AT = 8 °C contributes only about 10% to the plate height, the remainder arising from the fractionation of the molecular weight distribution. Thus a molecular weight distribution curve was obtained. We found the latter to be characterized by Mw/Mn s 1.52. We conclude that thermal FFF is applicable to ultrahigh molecular weight polymers but that other FFF subtechniques, especially flow FFF and sedimentation FFF, may also work in this molecular weight range.

Determination of the compositional heterogeneity of polydisperse polymer samples by the coupling of size-exclusion chromatography and thermal field-flow fractionation

“…Besides SEC, also thermal field-flow fractionation (ThFFF) can be used for the determination of the MMD of synthetic polymer samples [27][28][29][30][31]. ThFFF is performed in a thin open channel through which a carrier liquid, usually an organic solvent, is pumped.…”

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

“…1,2 Polymers subjected to such a thermal gradient migrate from the hot to the cold wall (accumulation wall) of the channel. This migration under a thermal gradient is termed thermal diffusion and is characterized by the thermal diffusion coefficient, D T .…”

Recent Advances in High-Temperature Fractionation of Polyolefins

“…In the SEC measurements such molar masses could not be detected due to shear degradation or the size exclusion limit. The presence of shear degradation during the HT-SEC measurements was verified by the comparison with off-line LALS measurements [198].…”