A novel tin-based POSS analogue, butylstannoxane dodecamer, was incorporated as chemically active nanofiller in epoxy resins and achieved a considerable anti-oxidative activity already near 0.05 wt% and very high activity near 1 wt%. The amino-functional nanofiller, which bonds as a linear segment, displayed a high reactivity towards the resin components during cure and was very poorly extractable. Interestingly, at elevated temperatures, the stannoxane nanofiller, whose functional substituents are attached by ionic bonds, displays a considerable short-range mobility in the matrix, and in course of a nano-phase-separation process, rearranges and polymerizes to needle-like nano-domains. This effect leads to additional crosslinking in the nanocomposite. This "solid-phase nano-precipitation" does not occur under oxidative conditions, where the nanofiller preferentially undergoes crosslinking with matrix chains and is thereby immobilized. Nanocomposite synthesis, characterization and the concentration dependence of the nanofiller effect are presented. (C) 2014 Elsevier Ltd. All rights reserved.