A model hybrid material based on a molten and flexible polymer -atactic poly(propylene oxide) (PPO) - tethered with a monofunctionalized POSS molecule incorporated at one or both chain ends was synthesized. Asymmetric PPO chains with a hydroxyl terminal group were first allylated, using a Williamson ether synthesis. Hydrosilylation of the allyl end-functionalized PPO chains with hydro-heptacyclopentyl-substituted POSS cages resulted in the anchoring of a single POSS unit per allyl functionality. Two distinct PPO-POSS nanocomposites were prepared: one with a large fraction of PPO chains having two POSS end-groups; one made of a hemi-telechelic singly substituted PPO-POSS chain. Both architectures contained a similar POSS content. The influence of the number of POSS end-groups per chain on the bulk organization was investigated by wide-angle X-ray diffraction. For each nanocomposite, part of the POSS particles crystallize but a propensity to form larger crystalline regions is observed as the fraction of di-telechelic PPO-POSS chains increases. These variations in the bulk organization of the POSS cages within the molten PPO matrix influence the thermal oxidative degradation behavior of the polymer matrix, as evidenced by thermogravimetric analysis. (C) 2009 Elsevier Ltd. All rights reserved.