The goal of this work was to investigate the properties of environmentally friendly, castor oil based polyurethane hybrid materials with titanium(IV) oxide nanoparticles, as a filler, and different types of diisocyanate (toluene diisocyanate and isophorone diisocyanate). In the sample synthesis, different ratios of the reactive groups (NCO/OH), r, were used (1, 1.15 and 0.92). In the composite preparation, only toluene diisocyanate was used, and the filler particles were premixed in a glass vessel with the castor oil polyol before the reaction with diisocyanate. For all the composite samples, the r value was 1. Polyurethane formation was confirmed by ATR-FT-IR by detecting the urethane band at 1515 cm(-1). It was determined that the hydroxyl groups had reacted because the broad band corresponding to the OH groups (3400 cm(-1)) was not detected or detected at a reduced intensity depending on the r value. As was expected, the presence of the unreacted NCO groups was detected only for samples with r > 1 (band at 2300 cm(-1), which corresponds to the existence of these groups). The dynamic mechanical measurements were performed at a temperature range from -50 degrees C to 100 degrees C at different frequencies. For investigation of reinforcement effect of filler on polymer matrix, tensile testing was applied. The glass transition temperature, T-g, was determined by DSC measurement. It was estimated that the T-g of the samples decreased as the nanofiller content increased due to the changes in the segmental mobility influenced by the interaction between the nanoparticles and polymer chains. (C) 2011 Elsevier B.V. All rights reserved.