A nylon 6 sample having average molecular mass 4.825 x 10(5) g mol(-1) was fractionated into five different fractions with respect to molecular mass, which ranged from 3691 to 999,000 g mol(-1). The light scattering and intrinsic viscosity measurements were made in m-cresol and its mixture with 1,4-dioxane. The second virial coefficient, radius of gyration and Mark Houwink's constant and unperturbed chain dimensions were determined by light scattering and viscosity measurement. It has been observed that all these parameters are composition of solvent and temperature dependent. The solvent having composition of 97% m-cresol and 3% dioxane, was best and it deteriorated with the increase/decrease in percentage of 1,4-dioxane in m-cresol. However, its thermodynamic quality was enhanced with the temperature. Such variation in quality of solvent was reflected in all the estimated parameters and showed maxima at this composition of solvent. The unperturbed dimensions obtained by different methods though, differed in values but showed same trend and NA-MKB method gave close results to the one obtained through [eta(o)]. A new expression has also been proposed relating k(o) to solvent quality and temperature and the data obtained by us for nylon-6 and the one obtained from the literature for dextran obeyed this expression up to large extent irrespective of the solvent composition and temperature. The proposed equations have also been applied to dextran/methoxy ethylene and dextran/ethylene glycol systems and worked well. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 2351-2358, 2011