Osmotic pressures of moderately concentrated polydimethylsiloxane solutions

Osmotic pressures of polydimethylsiloxane in chlorobenzene, toluene, and cyclohexane were measured over a wide range of concentration (0 < v 2 < 0.25). A peculiar behavior of an apparent second virial coefficient, observed by others, was not observed in a transition region ( c ≈︁ 0.05). The data were used for evaluating the excluded‐volume parameter z. The theories of the excluded‐volume effect were tested with the z values estimated. In the limit of z examined the modified Flory‐Fox relation seems to fit the observed dependence of the expansion factor α 0 3 on z .