Polyhedral oligomeric butyl stannoxane cages (Sn-POSS) as oxidation-activated linear repairing units or crosslinking nano-building blocks, depending on structure of the polymer matrix

The chemically active heavier POSS homolog, the n-butylstannoxane dodacamer cage, shows unusual stabilizing properties during an oxidizing treatment of organic-inorganic hybrid polymer materials, into which it is incorporated as nano-building block. In this work, we dispersed Sn_POSS in several matrixes, which mainly had all-carbon backbones (based on polystyrene, polyacrylates and polyethers). Sn_POSS concentration was varied, and it was incorporated either as non-functional cage (blending), or via covalent bonding as a large co-monomer. The stannoxane cages' reactivity in the different matrixes was compared, and the authors propose matrix-dependent mechanisms of the stabilizing effect of Sn_POSS, which make possible to predict the behavior of this cage in different polymers, if their degradation mechanism and eventual reactivity of pendant groups can be estimated. Under oxidizing conditions, the studied matrixes yielded either pendant radicals on (at first) intact chains, or terminal radicals on ends of fragmented chains, depending on the exact polymer structure. The stannoxane cages, if present, subsequently underwent either crosslinking, or chain-repair reactions (fragmented chains re-connection) with the radical sites of the matrix. Another reaction type, which yielded additional crosslinking in the hybrids, was observed in case that the polymer matrix contained suitable pendant functional groups, which were able to react with Sn_POSS after activation either by heat or by oxidation.