On the heat of solution of polymer with solvent: Polydimethylsiloxane–solvent systems

Heats of mixing and excess volumes at infinite dilution have been obtained at 25°C. for polydimethylsiloxane or its lower oligomers in various solvents by using a twin conduction microcalorimeter and from the pycnometric specific volumes. From those values, excess energies ΔE^M_v at constant volume have been determined. The prediction on intramolecular conformation contributions to the heat of solution as proposed by Bianchi has been evaluated by the values of ΔE^M_v. The heat of solution in the polymer–solvent systems was interpreted by the expression for ΔE^M_v derived from the Van Laar-Hildebrand work on simple liquid mixtures with the solubility parameters of polymers obtained from indirect measurements. The values of conformational intramolecular energy change calculated from dilute solution properties were difficult to rationalize with our results. Our present results suggest that systems in a nonideal state can not be distinguished for certain from those in the ideal state. This conclusion based on apparent values does not deny the possible effect of the conformational energy change.