Poly(methyl methacrylate)/TiO2 nanocomposites have been prepared by the polymerization with photoexcited TiO2 nanoparticles as initiator. To reveal the interfacial structure, the composites obtained are investigated by FTIR and XPS analysis. The bound PMMA displays triply split IR bands attributed to the carbonyl stretching mode, meanwhile great changes also occur in the IR range closely related to the conformation of PMMA. Based on the area of the nonassociated and associated PMMA carbonyl stretching peaks in the FTIR spectrum, it is calculated out that the bound PMMA is constituted of 70% repeating units in nonassociated state and 30% units associated to TiO2 inorganic nanoparticles. Moreover, XPS analysis show that Ti2p doublet of the composites shift to lower binding energy by 1.0 eV, indicating the interaction between Ti atoms of TiO2 and oxygen atoms of PMMA. According to the observation that the interaction involves both carboxyl and carbonyl groups of PMMA, a bidentate complex is approved. In addition, compared with the extracted PMMA, certain backbone chains of bound PMMA have to change their rotational conformations from gauche to trans so as to bond to the surface active centers at TiO2 nanoparticles. (c) 2008 Wiley Periodicals, Inc.