EFFECTS OF SOLVENT COMPOSITION ON POLYMER RETENTION IN THERMAL FIELD-FLOW FRACTIONATION - RETENTION ENHANCEMENT IN BINARY SOLVENT MIXTURES

The thermal FFF retention of 11 linear polystyrene polymer standards in the molecular weight range 9000-1,860,000 Daltons in 15 single-component solvents and similar to 30 binary solvent mixtures has been measured and compared. The results have been converted by theory into the calibration constants phi(0) and n describing the molecular weight dependence of retention and into values of the thermal diffusion factor alpha, which specify the strength of the underlying thermal diffusion phenomenon. Retention is found to be enhanced considerably for certain binary mixtures. The binary solvent consisting of 70% (by volume) tetrahydrofuran (THF) and 30% dodecane yields retention parameters similar to 60-65% as large as those measured in pure THF; the increased retention is theoretically capable of extending the working range of thermal FFF to polymers having only half the molecular weight of the lower molecular weight limit found for THF.