AbstractViscometric and osmometric studies have been carried out with fractions of poly(mmethyl styrene) in solutions of benzene, cyclohexane, and ethyl acetate at 30, 40, and 50°C. The values of K′ and ‘a’ in the KUHN‐HOUWINK relation have been reported for the above polymer‐solvent systems. The values of unperturbed dimension, (r 20/M)1/2, solvent polymer interaction constant (B) and conformational parameter (σ) have been computed applying the theories of FLORY‐FOX‐SCHAEFGEN, KURATA‐STOCKMAYER‐ROIG, and STOCK‐MAYER‐FIXMAN. The applicability of the theories of FLORY, KURATAet al.,and PTITSYN has been critically analysed from the dependence of the expansion factor (α) on molecular weight. Values of thermodynamic parameters, Θ, Ψ1,x1, and X