Equilibrium vapor pressures were measured for the systems toluene/poly (dimethylsiloxane) [two different polymers, 35-55 °C] and cyclohexane/poly(vinyl methyl ether) [three polymers, 35-65 °C] by combining a head-space sampler with a gas chromatograph. The Flory-Huggins interaction parameters calculated therefrom as a function of the volume fraction 2 > 0.5, in contrast to the general perception. This observation is tentatively explained in terms of changes in coil dimension taking place in the region of high polymer concentrations. Furthermore, ( 2) may exhibit a minimum even with the common polymers of present interest. In all cases the concentration dependence of is described well by a series expansion of with respect to 2 up to the fourth term, if two parameters are adjusted. The temperature dependence of at different concentrations demonstrates that the heats of dilution generally increase with increasing 2, whereas the noncombinatorial entropy of dilution decreases. This situation leads to a linear interdependence of the enthalpy and entropy part of . With the system toluene/poly-(dimethylsiloxane) one observes an inversion of the heat effects upon an increase of 2 from exothermal to endothermal at ca. 13 vol %.

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Continuous polymer fractionation (CPF) -a new large-scale method -was applied to the technical poly(methy1 vinyl ether) (PVME) using toluene as solvent and petroleum ether as nonsolvent. TWO different devices served as fractionation apparatus, namely a column packed with glass beads and a set of mixer-settler extractors. Advantages and draw-backs of these devices are discussed. The experiments yielded numerous PVME fracti?ns, varying in molar mass from 22 to 87 kg/mol and in molecular non-uniformity U = (M,,,/M,) -1 from 0,25 to 0,41 according to gel-permeation chromatography as compared with ca. U = 1,30 for the starting material. The following Kuhn-Mark-Houwink relation was established for PVME in ethyl methyl ketone at 30 "C: [q]/(mL/g) = 2,6 * @,86.

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SUMMARY:Flory-Huggins interaction parameters x were determined by means of equilibrium vapor pressures (measured via a combination of a head-space sampler with a gas chromatograph) and light scattering as a function of composition and temperature for the systems cyclohexanone/polystyrene [CHO/PS] and cyclohexanone/poly(butyl methacrylate) [CHO/PBMA].The investigation of molecular weight influences on x with the system CHO/PBMA demonstrates that they persist almost up to the pure polymer. In order to rationalize this result, it is postulated (in accord with experimental findings and theoretical predictions) that the dimensions of polymer chains may vary upon the addition of solvent even in highly concentrated solutions. From the information concerning x (7") the interaction parameters were split into their enthalpy and entropy part. In the case of CHO/PS these quantities vary considerably with composition and turn out to be linearly interrelated.