Polyhedral oligosilsesquioxane (POSS)-reinforced thermosets based on octaglycidyl epoxy polyhedral oligosilsesquioxane cured with 4,4Ј-diaminodiphenyl sulfone (DDS) were prepared and studied for their cure, thermomechanical, and microstructural characteristics. Particular attention was paid to nanometer-scale deformation processes responsible for toughening, as revealed by transmission electron microscopy (TEM) in conjunction with the thermal properties. A cure analysis investigated with calorimetry and rheometry showed a significant dependence of the cure mechanism and kinetics on the DDS content, but all hybrid thermosets reacted completely below 300°C into rigid solids. A dynamic mechanical analysis of this hybrid resin system showed that increasing the DDS concentration used during cure increased the dynamic storage modulus in the glassy (temperature Ͻ glass-transition temperature) and rubbery (temperature Ͼ glass-transition temperature) states, simply through an increase in the crosslink density. The phase structures revealed by TEM with selective POSS staining were drastically affected by the DDS concentration and manifested as altered nanomechanical deformation structures. It was qualitatively found that the main toughening mechanism in the studied POSS-reinforced thermosets was void formation at the nanometer scale, possibly templated by limited POSS aggregation. As the crosslinking density increased with the DDS concentration, microshear yielding between voids prevailed, providing a balance of stiffness, strength, and toughness.

We use molecular dynamics to calculate the structural, elastic, and polar properties of crystalline ferroelectric β -poly(vinylidene fluoride), PVDF (-CH 2 -CF 2 -) n with randomized trifluoroethylene TrFE (-CHF-CF 2 -) n as a function of TrFE content (0-50%) in the temperature range of 0-400 K. There is a very good agreement between the experimentally obtained and the computed values of the lattice parameters, thermal expansion coefficients, elastic constants, polarization, and pyroelectric coefficients. A continuous decrease in Young's modulus with increasing TrFE content was observed and attributed to the increased intramolecular and intermolecular repulsive interactions between fluorine atoms. The computed polarization displayed a similar trend, with the room temperature spontaneous polarization decreasing by 44% from 13.8 µC/cm 2 (pure PVDF) to 7.7 µC/cm 2 [50/50 poly(VDF-co-TrFE)]. Our results show that molecular dynamics can be used as a practical tool to predict the mechanical and polarization-related behavior of ferroelectric poly (VDFco-TrFE). Such an atomistic model can thus serve as a guide for practical applications of this important multifunctional polymer. . Fax:+1 860 486 2981; Tel:+1 860 486 2012 ‡ These authors contributed equally to this work. J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 1-8 | 1

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