Pure poly(N-vinyl-2-pyrrolidone) (PVP) and P(VP-crotonic acid) [P(VP/CrA)] copolymers with different CrA contents were prepared by the gamma-ray-induced polymerization technique. The change in the surface free energy of the copolymers was investigated using the Van Oss-Good contact angle evaluation methodology in order to estimate their wettability properties. The apolar Lifshitz-van der Waals component (gamma(S)(LW)) and the electron donor component (gamma(S)(-)) of the PVP network were calculated as 27.6 and 56.5 mN m(-1), respectively. In this case, the surface of the PVP network had a basic character (electron donor). By contrast, the gamma(S)(LW) component of P(VP/CrA) copolymers increased and then remained almost constant with increasing CrA content. In addition, the surface of these copolymers changed from a basic character (gamma(S)(-) = 56.5 mN m(-1)) to an acidic character (gamma(S)(+) = 0.07 mN m(-1)) with increasing CrA contents in the copolymer. (C) 2003 Wiley Periodicals, Inc.