Epoxy resin containing polyphenylsilsesquioxane: Preparation, morphology, and thermomechanical properties

Polyphenylsilsesquioxane (PPSQ) was incorporated into an epoxy resin to prepare organic-inorganic composites, and two strategies were adopted to afford composites with different morphologies. Phase separation induced by polymerization occurred in the physical blending system. However, nanostructured composites were obtained when a catalytic amount of aluminum triacetylacetonate was added to mediate the reaction between PPSQ and diglycidyl ether of bisphenol A (DGEBA). The intercomponent reaction significantly suppressed the phase separation on the micrometer scale. Organic-inorganic composites with different morphologies displayed quite different thermomechanical properties. Both differential scanning calorimetry and dynamic mechanical analysis showed that the nanostructured composites possessed higher glass-transition temperatures than the phase-separated composites with the same loading of PPSQ, although the intercomponent reaction between PPSQ and DGEBA reduced the crosslinking density of the epoxy matrix. This result was ascribed to the presence of nanosized PPSQ domains in the nanostructured composites, which acted as physical crosslinking sites and thus reinforced the epoxy networks. The nanoreinforcement of the PPSQ domains afforded the enhanced dynamic storage modulus for the nanostructured composites in comparison with the phase-separated composites with a PPSQ concentration less than 15 wt %. In terms of thermogravimetric analysis, the organic-inorganic composites displayed improved thermal stability and flame retardancy. (c) 2005 Wiley Periodicals, Inc.