Covalently immobilized poly(4-vinylphenol) (PVP) monolayer films were fabricated by spin coating PVP on perfluorophenyl azide (PFPA)-functionalized surfaces followed by UV irradiation. The pH-responsive behavior of these PVP ultrathin films was evaluated by ellipsometry, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). By monitoring the responses of these films to pH in situ, the ionization constant of the monolayer thin films was obtained. The apparent plc, value of these covalently immobilized PVP monolayers, 13.4 by SPR, was 3 units higher than that of the free polymer in aqueous solution. (C) 2015 Elsevier B.V. All rights reserved.