Viscosities were measured as a function of pressure and temperature with solutions of PVC 75 000 in cyclohexanone (CHO) and polymer contents ranging from 0,6 to 12 wt.-%, by means of a Searle-type (≥3 wt.-%) and a rolling-ball viscometer (<3 wt.-%). Furthermore, the influence of molecular weight was determined with solutions of 8 wt.-% of PVC 20 000, PVC 37 000 and PVC 100 000. (The numbers in the codes of the PVC specimens are their approximate molecular weights.) For all concentrations and molecular weights, the viscosity increases in a more or less exponential manner with increasing pressure. The ratio f1000 of the viscosity of the solution at 1 000 and 1 bar can be varied by the change …

Viscosity measurements were carried out as a function of pressure and temperature with solutions of 8 wt.-% PVC (Mw ≈ 75 000) in ten thermodynamically good solvents by means of a Searle-type viscometer. A rollingxyhball viscometer was used for the investigation of the pure solvents. In all cases the viscosity increases in a more or less exponential manner when the pressure is raised. The viscosity ratio f1000 = η1000 bar/η1bar can be varied by the choice of the solvent from ca. 2 (tetrahydrofuran) to 3,0 (cyclohexanone) at 40°C. For a constant temperature of 40°C, the volumes of activation for the viscous flow of the solutions, V≠, or f1000 exceed that of the pure solvent, by typically 25%.…

A new Continuous Polymer Fractionation method, called CPF, is described. The polymer to be fractionated is dissolved in a solvent/non-solvent mixture, and this solution (feed) is extracted continuously by a second liquid (extracting agent), which contains the same solvent components as the feed. In the case of PVC, the fractionation was carried out with a pulsed counter current extraction apparatus and THF/water was used as solvent/non-solvent mixture. Fractionation is achieved by the fact that the molecules are distributed over the counter current phases according to their chain length; the feed leaves the column as gel and the extracting agent as sol. First some explorative experiments we…

From the break-down in the viscosity and from the increase of the intensity of the scattered light, associated with the entrance into the two-phase region, the pressure dependence of the demixing temperature of solutions of PVC 37 000, PVC 75 000 and PVC 100 000 in phenetole and PVC 75 000 in o-xylene was measured up to 1 000 bar. (The numbers in the codes of the PVC specimens are their approximate molecular weights.) The application of pressure increases the demixing temperatures of PVC in both solvents by about 1 K/100 bar. For a qualitative forecast of the pressure effects, the solubility parameter theory in combination with the corresponding states principle, and an empirical correlatio…

Continuous fractionation and solution properties of PIB. I. Search for the best mixed solvent and first results of the continuous polymer fractionation

To adopt a recently developed method for large scale fractionation (CPF = continuous polymer fractionation, a special kind of counter current extraction) to polyisobutylene (PIB), a systematic search for the best mixed solvent was performed. For this purpose, the essential parts of the phase diagrams solvent/nonsolvent/PIB were determined for 21 mixed solvents by cloud-point measurements; with eight systems of special interest, the molecular weight distributions of the polymers contained in the coexisting phases were also studied. On the basis of these experiments and of considerations concerning additional criteria for the performance of the continuous counter current extraction, the mixed…

Using a self-constructed light scattering apparatus, the pressure dependence of the demixing temperature of solutions of PVC 20 000, PVC 37 000 and PVC 70 000 in THE/water was determined up to 1 000 bar for different compositions of the mixed solvent. (The numbers in the codes of the PVC specimens are their approximate molecular weights.) In contrast to the thetasolvents o-xylene and phenetole, the solubility decreases with increasing pressure for all molecular weights and compositions under investigation typically by about 1 K/100 bar. The evaluation of the experimental findings demonstrates that the volume fraction of the nonsolvent in the mixed solvent, φ, is the variable that governs ph…

Investigations with ca. 100 organic liquids in a temperature range from −20°C to 90°C result in a survey of the solubility behaviour of PVC. The experimental results were compared with the predictions of the solubility parameter theory: Accepting δ = 9,75 (cal/cm3)1/2 as the solubility parameter for PVC, all solvents (except ketones in which PVC is soluble independent of their solubility parameters) are located within the range of δPVC ± 0,75. Only three of the 100 liquids examined turned out to be (endothermal) theta-solvents, namely the aromatic solvents o-xylene, phenetole and dimethyl phthalate. The theta-temperatures in o-xylene and phenetole were determined viscometrically by means of…

CPF: A New Method for Large Scale Fractionation

The paper demonstrates how the Continous Polymer Fractionation (CPF) functions and how it has been applied to polyvinylchlorid.