The instrinsic viscosities of five fractions of polydimethylsiloxane in the molecular weight range .Mη= 2.8×105-2.5×106 were determined in two θ-solvents

butanone (Tθ= 20℃) and bromobenzene (Tθ=78℃). Viscometric data of both systems conform to the relationship [η]θ = KθM0.50 with Kθ= 6.80×10-2 and 7.73×10-2 in butanone and bromobenzene respectively. The value of △1n[η]θ/△1nT thus obtained from thevalues of Kθ at two θ-temperatures is 0.71. Using the Flory-Fox theory of intrinsicviscosity

we get d 1n h02/d-dlnT=0.47. The value is higher than that obtained in the ethyl-benzene-diethylphthalate mixed solvent system.