A new silicon-containing spiroorthoester, 1,4,6-trioxaspiro [4,4]-2-nonylmethyl 3-trimethylsilyl propionate (SOE-Si), was synthesized with good yield by an esterification reaction with a previously synthesized 2-hydroxymethyl-1,4,6-trioxaspiro [4,4] nonane (SOE-OH) and trimethylsilyl propionic acid. The structure of the new SOE-Si was confirmed by H-1 and C-3 NMR. The SOE-Si and a mixture of DGEBA/SOE-Si were polymerized with ytterbium triflate as a cationic initiator. The curing was studied with differential scanning calorimetry (DSC) and monitored by Fourier transform infrared (FTIR) spectroscopy. The materials were characterized with DSC, termogravimetric analysis (TGA) and thermodynamomechanical analysis (DMTA). The volume change was evaluated with a Micromeritics gas pycnometer and the flame retardancy was tested by the limiting oxygen index (LOI) measurements. (c) 2007 Wiley Periodicals, Inc.