A simple expression for the composition dependence of the Flory‐Huggins interaction parameter of polymer/solvent systems reported earlier is used to model the demixing of polymer solutions into two liquid phases. To this end, the system specific parameters ζ and ν of that approach are calculated as a function of temperature using the thermodynamic expressions resulting for the critical conditions on one side and from experimentally determined critical data for polymers of different molar mass on the other side. By means of data reported for the system cyclohexane/polystyrene it is demonstrated that binodal and spinodal lines are very accurately modeled at low temperatures (UCSTs) and at high temperatures (LCSTs). The parameters obtained from the demixing behavior match well with that calculated from the composition dependence of the vapor pressure at temperatures where the components are completely miscible. Information on the phase separation of the system trans‐decalin/polystyrene for different molecular weights and at different elevated pressures is used to show that the approach is also apt to model pressure influences. The thus obtained ζ(T;p) and ν(T;p) enable the prediction of the (endothermal) theta temperature of the system as a function of pressure in quantitative agreement with the data directly obtained from light scattering measurements with dilute solutions.

Solutions of 1,4-polybutadiene (1,4-PB, 98% cis) and of 1,2-polybutadiene (1,2-PB) in n-butane (n-C 4) were studied with respect to their vapor pressure and to their demixing into two liquid phases under isochoric conditions within the temperature range from 25 to 75 °C. 1,2-PB mixes homogeneously with n-C 4 at any ratio, in contrast to 1,4-PB, which exhibits a miscibility gap extending from practically pure solvent to approximately 40 wt % polymer. Corresponding to these solubility differences, the vapor pressures for the system n-C 4/1,4-PB are considerably higher than for n-C4/1,2-PB at the same concentration and temperature. The experimental results are modeled accurately and consistently by means of a modified Flory-Huggins approach accounting explicitly for chain connectivity and conformational variability of the polymers. The vapor pressures calculated by means of the Sanchez-Lacombe theory agree very well with the experimental data for both systems; this approach fails, however, in the case of the liquid/liquid phase equilibria because it predicts similar miscibility gaps for both polymers. The modified Flory-Huggins approach explains the fundamentally different solubility of 1,2-PB and 1,4-PB in terms of pronounced dissimilarities in their conformational response to dilution, which is in the case of 1,4-PB strongly impeded by the double bonds of the main chain.

For solutions of cellulose (Solucell, M w ¼ 230 kg mol À1 ) in the mixed solvent DMAc (N,N-dimethylacetamide) + LiCl, it is demonstrated by means of an electrolysis cell, subdivided into six compartments, that cellulose migrates to the anode. This observation is interpreted in terms of a field-induced opening of associations between the [DMAc] x Li þ complex and the [cellulose]Cl À complex. This understanding is corroborated by the observed changes in the positions of the menisci in the electrode compartments of the electrolysis cell. Contrary to expectations, the rate of cellulose transport does not depend on its molar mass, at least under the present conditions.

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