The intrinsic viscosities of twelve fractions of polydimethylsiloxane (Mη = 9.1×104-6.0×106) were determined in heptane and toluene solutions at 25℃. The values ofexpansion factor calculated from the Flory-Fox theory of intrinsic viscosity
α3 = [η]/[η]θ
givelinear plots of α5-α3 vs Mnnnnnnn1/2
and the molecular weight dependence of a is not in accord with the theory of Kurata-Stockmayer-Roig.