Samadi, F., Eckelt, J., Wolf, B.A., Schüle, H., Frey, H.
"Branched versus linear oligo(dimethylsiloxane): Differences in their thermodynamic interaction with solvents"
Journal of Polymer Science Part B-Polymer Physics 2010, 48, 1309-1318.
Abstract: The thermodynamic behavior of the solutions of two types of oligo(dimethylsiloxane) (O-DMS) was studied by means of vapor pressure measurements and vapor pressure osmometry at different temperatures for the thermodynamically favorable solvent THF. The branched material required for that purpose was synthesized and fractionated by means of the single solvent acetone in order to eliminate components of low degrees of branching. The Flory-Huggins interaction parameters, c, for the systems THF/O-DMS as a function of composition pass a minimum at all temperatures (25, 40 and 60 °C) in the case of the branched material. For the unbranched polymer the minimum is only observed at 60 °C, at the two lower temperatures the dependence is linear and identical. This exceptional behavior is tentatively attributed to the formation of favorable orientational order in the pure state at sufficiently low temperatures. At high oligomer concentrations THF interacts more favorably with the branched material, however, this preference is reversed upon dilution. All measured composition dependencies of c can be modeled quantitatively by an approach accounting for chain connectivity and for the ability of the oligomers to change their conformation upon dilution.
preprint number: 302