Synthesis and Characterisation of Metal Isobutylsilsesquioxanes and Their Role as Inorganic-Organic Nanoadditives for Enhancing Polymer Thermal Stability

Metal isobutylsilsesquioxanes (M‐POSS) with TiIV and VV metal centres have been prepared by direct corner‐capping of trisilanolisobutyl‐POSS (1). The synthetic procedure has been followed in solution by FTIR spectroscopy and samples have been characterised by 29Si{1H} NMR, FTIR, FT‐Raman and UV/Vis spectroscopy in order to study the structure and the chemical properties of the transition metal centres incorporated in the synthesised compounds. The corner‐capping reaction basically lead to tetrahedrally coordinated metal centres inserted in the siliceous cage. The hybrid inorganic–organic nature of these compounds and the possibility of dispersing catalytically active metal centres in a highly efficient way within organic matrices have been investigated by dispersing the title compounds at 3 wt.‐% in a polypropylene matrix by melt blending, which leads to nanocomposite materials. A study of the thermal degradation of polypropylene, trisilanolisobutyl‐POSS and metal‐isobutyl‐POSS composites shows a significantly enhanced thermal stability under oxidative conditions only when metal‐containing silsequioxanes are dispersed, along with an extended formation of condensed polyaromatic compounds (charring products). This evidence is consistent with a possible catalytic effect favouring oxidative dehydrogenation of the polymeric organic chains occurring in the condensed phase under combustion conditions, and highlights a possible promising use of M‐POSS as fire‐retardant additives for polymers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)