An osmometer is described which is applicable to highly viscous concentrated polymer solutions. Results are presented for polyisobutylene (MW = 90,000) in cyclohexane at 30 and at 8°, and in benzene at 24.5° (the theta point) and at 50°. Concentrations ranging up to 20% (w/v) and 29%, respectively, were used. The results are compared with the semiempirical formulation of the chemical potential: In cyclohexane χ1 = 0.429 at 30°, and 0.434 at 8°; higher parameters may be neglected. These observations stand in excellent agreement with results of vapor pressure measurements on more concentrated solutions, with parameters derived from intrinsic viscosities, and with the second virial coefficient observed at higher dilutions. The results in benzene at 24.5° lead to χ1 = 0.500 and x2 = 0.31; at 50°, χ1 = 0.485 and x2 = 0.29. The values of χ1 are compared with deductions from instrinsic viscosities and from second virial coefficients. The fact that the critical miscibility point for M = ∞ occurs at v2 = 0 for this system requires x2 < 1/3.

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Intermediate heats of dilution, heats of mixing, and heat capacities have been measured in the dilute and intermediate concentration ranges for the polyethylene oxide) (PEO)-water and PEOwater-ethanol systems. Heats of dilution are exothermic for all systems and pass through a minimum at 50% by weight of ethanol. Heats of fusion of PEO in water and in 50% water-ethanol calculated from the combined heat of dilution and heat of mixing results are 9564 and 10 224 J basemol"1, respectively. Apparent basemolar heat capacity (CPi0) has been determined for PEO. In water, results show that CPi# decreases with increasing concentration and that Cp¿ at infinite dilution decreases with decreasing molecular weight. The value of 0" increases with increasing temperature. Values of CPi0 in water-ethanol go through a minimum at 30% by weight of ethanol. The results do not support very strongly the existence of an ordered structure for PEO in solution in water. However, they are in very good agreement with the conclusion of a recent light scattering study of the same system assuming that aggregates coexist with molecularly dispersed PEO.

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