The unperturbed dimensions and thermodynamic parameters of poly(N-vinyl-2-pyrrolidone) (PVP) were studied in aqueous solutions in the presence of certain phenolic cosolutes (phenol, catechol, hydroquinone, resorcinol, and phloroglucinol). The intrinsic viscosities at 25degreesC and the theta temperature, linear and thermodynamic expansions, and root mean square end to end distances were evaluated for the system that was employed. The sequence was obtained due to the effectiveness of the cosolutes in the order of phloroglucinol > resorcinol > hydroquinone > catechol > phenol. The effects of these cosolutes on the main thermodynamic parameters were reported to be due to the number and position of hydroxyl groups present. The thermodynamic interaction parameter was also evaluated and the enthalpic and entropic contributions were verified. The condition required for the theta temperature to correspond to a Flory interaction parameter of 0.5 was well provided, yielding a theta temperature of almost 0.5 for the system under study. (C) 2002 John Wiley Sons, Inc.