Thermally induced polymerization of multifunctional methylmethacrylate POSS (MMA-POSS) was studied in this work for preparation of polymer/POSS nanocomposites. The polymerization of MMA-POSS could be promoted with benzoyl peroxide (BPO). Self-assembly of POSS into a layer-by-layer structure in the MMA-POSS polymer (TP-MMA-POSS) is observed with a transmission electron microscopy. An ultra-low-k value of about 1.85 is measured with TP-MMA-POSS. In addition, polyimide-POSS nanocomposites are also prepared. These nanocomposites demonstrate good homogeneity and enhanced mechanical properties. (C) 2008 Wiley Periodicals, Inc.