In this study, in situ modified phenol formaldehyde resins were prepared from hydroxyl terminated polydimethyl siloxane (DH.PDMS), clay (montmorillonite) in the presence of base catalyst. Different clay contents (0.5, 1, 3, 5 wt %) were used to produce DH.PDMS modified resol/clay nanocomposite resins (DH.PDMS-LC-PFRs). DH.PDMS-LC-PFRs were partially cured by heat, and the effects of the curing process and the clay content in the resol resin were determined on the spectroscopic, thermal, mechanical and microscopic properties of the final products. Furthermore, the effects of the reaction time on the polymerization and on the morphology of the materials were investigated. The structures of the specimens were characterized by means of Fourier Transform Infrared (FTIR-ATR) spectroscopy. Thermal properties of the samples were determined with Differential Scanning Calorimeter (DSC) and Thermogravimetric Analyzer (TGA). Mechanical properties of the specimens were determined by Dynamic Mechanical Analyzer (DMA). The obtained samples were also characterized morphologically by Scanning Electron Microscope (SEM). (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013