6533b86efe1ef96bd12cbc5e

RESEARCH PRODUCT

false

subject

description

The demixing behavior of 20 representatives of the system oligo(dimethylsiloxane)/oligo(propylene glycol) (ODMS/OPG)1 is investigated at pressures up to 1 500 bar. The degrees of oligomerization range from 2 to 5 for the first and from 1 to 57, 6 for the second component. The experimental results are compared with those for the previously studied system oligoisobutene/oligo(propylene glycol) (OIB/OPG). In both cases the observed upper critical temperatures Tc increase with the number of monomeric units of the less polar component, whereas they run through a minimum when the number of monomeric units of the glycol is raised. For the present system the Tc values are found to be considerably higher than that of OIB/OPG and the optimum compatibility can normally be observed already between 1 and 7 propylene glycol units as against 50 in the case of OIB/OPG. In the low pressure region Tc of ODMS/OPG is decreased by pressure for all representatives of this system, while enhanced incompatibility has been found with OIB/OPG. For ODMS/OPG the special features of the critical lines are determined by the chain length of OPG, for OIB/OPG by that of OIB. For ODMS/OPG the initial reduction of Tc by pressure is most pronounced with the highest molecular weight oligo(propylene glycol), for which it amounts up to 0,3 K/bar; with increasing pressure and decreasing chain length the effects become smaller. For the lowest molecular weight sample of OPG the critical lines show a vertex at 700–1000 bar. In any case the two systems under consideration behave in an increasingly similar manner as the pressure is raised. The theoretical evaluation and discussion of the above results is performed by analogy with that of the first paper in this series.