Diacrylate compounds derived from alpha-pinene and limonene (TDAs: TDA-1 and TDA-2) were photocured with methacryl-substituted polysilsesquioxane (ME-PSQ) prepared from 3-(trimethoxysilyl)propyl methacrylate and tetramethylammonium hydroxide (TMAOH) in the TDA/ME-PSQ weight ratio of 20 : 0, 20 : 1, 20 : 2, 20 : 3, and 20 : 4. All the photocured TDA/ME-PSQ hybrid nanocomposites became transparent. The thermomechanical analysis of the cured TDA/ME-PSQ revealed that the glass transition temperature (T-g) increased, the thermal expansion coefficient above T-g decreased with increasing ME-PSQ content, and that the TDA-1/ME-PSQ had ca. 30 degrees C greater T-g than the TDA-2/ME-PSQ with the same ME-PSQ content. Also, the dynamic mechanical analysis revealed that the TDA-1/ME-PSQ had much greater storage modulus at around 150 degrees C than the corresponding TDA-2/ME-PSQ. The flexural strength and modulus of the TDA/ME-PSQ nanocomposites at 20 degrees C had maximum at ME-PSQ content 4.8 and 13.0 wt %, respectively. As a whole, the thermal and mechanical properties of the nanocomposites were improved by the addition of ME-PSQ, and those of TDA-1/ME-PSQ nanocomposites were superior to those of TDA-2/ME-PSQ. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 3326-3331, 2010