The effect of quaternary ammonium functionalised polyhedral oligomeric silsesquioxane (POSS) on the self-polymerisation of the diglycidyl ether of bisphenol A (DGEBA) and on the DGEBA-Jeffamine-T403 curing was investigated by differential scanning calorimetry. The acidic ammonium groups of POSS were found to catalyze the self-polymerisation of DGEBA but termination reactions severely compete with the propagation and only low conversions in epoxy groups are attained (<20%). A reaction between POSS and DGEBA was revealed at the POSS-matrix boundary suggesting the release of amino functionality of POSS during thermal cure. The catalytic effect of POSS over the epoxy-amine reaction was also demonstrated. The efficiency of this catalytic effect was found to be significantly dependent on the processing conditions. Finally, two competitive effects were found to affect the glass transition temperature of POSS modified epoxy networks cured under dynamic conditions. It is proposed that the inclusion of POSS at the nanometer scale is responsible for the increase in free volume of the system which results in the depression of T-g's while a restriction effect of POSS cages on polymer chain motions (enhanced T-g's) is associated to the development of POSS aggregates in the networks with high POSS loadings. (C) 2009 Elsevier B.V. All rights reserved.