Behavior of tin-based "super-POSS" incorporated in different bonding situations in hybrid epoxy resins

Hybrid organic-inorganic epoxies containing the heavier POSS homologue, n-butylstannoxane dodecamer, incorporated as an inert block, as a linear unit, and as a network junction were prepared. This nanometer-sized inorganic cage is especially attractive because of its chemical reactivity (besides mechanical matrix reinforcement). It can undergo oxidative cross-linking reactions with the matrix, or at elevated temperature in the absence of air, it can oligomerize to larger nanodomains, thus generating additional chemical cross-links. The influences of the bonding situation of the stannoxane cages on the hybrid resins morphology, mechanical properties, and on the cages chemical activity were studied. The highest reactivity was observed in the case of the linearly bonded cages, which also can achieve unusual short-range mobility in the matrix at high temperatures. This mobility was found to be a result of reversible oxonium ionic bonds to the linear units. The branching stannoxane units display a fair antioxidative reactivity in the matrix, which is nevertheless markedly smaller than in the case of the linear ones. On the other hand, the branching cage achieves the highest mechanical reinforcement of the matrix. The nonbonded stannoxane displays macroscopic phase separation at concentrations above 4 wt % and does not reinforce the matrix markedly, but at low concentrations, it is highly efficient in counteracting the oxidative degradation of the matrix. The effect of the stannoxane cages was also systematically compared with the effect of similarly incorporated POSS cages in the same matrix and in general.