Investigation of pre-reaction and cure temperature on multiscale dispersion in POSS–epoxy nanocomposites

Dispersion of monoamine-functionalized polyhedral oligomeric silsesquioxane (POSS) in an epoxy network was improved by pre-reacting the POSS with excess epoxide and employing a high-temperature cure. DGEBA/DDS networks were formulated with 2.5 and 10 wt% POSS. In some samples, POSS was pre-reacted with DGEBA. The hybrid materials were characterized via SEM, TEM, and DMA. The microscopy and DMA results evinced a multiscale morphology with POSS-rich glassy domains, nano- and microcrystallites, and crystallite agglomerations. For a loading level of 2.5 wt% POSS, the sample with unmodified POSS cured at 125 °C had inorganic crystallites on the order of 1–5 μm and agglomerations on the order of 10–20 μm, whereas the sample with pre-reacted POSS cured at 180 °C had near-perfect dispersion with no agglomerations and very few POSS crystallites. The 10 wt% POSS epoxies also showed improved dispersion with pre-reaction and increasing cure temperature. The dispersion improvements were attributed to the enhanced miscibility of the pre-reacted POSS and the increased rate of POSS reaction into the growing epoxy network at a higher cure temperature.