The influence of silica nanoparticles with epoxide groups at the surface on the cationic polymerisation of cycloaliphatic epoxides is shown. When cyclohexene oxide is the monomer the gel content of the polymer increases with increasing amount of the multifunctional particles. The insoluble part of the polymer consists of particles with a silica core and a polymer shell. The core-shell-particles are connected to each other. In the case of a diepoxide as the monomer the storage modulus increases with increasing amount of particles. This is particularly the case for very high loadings. The glass transition temperature of the sample decreases with increasing amount of functional filter and the swelling rate with a solvent goes through a minimum. It is proposed that the particles are surrounded by a softer polymer layer compared to the bulk polymer. This is due to chain transfer reactions with water adsorbed on the particle surface. (c) 2005 Elsevier Ltd. All rights reserved.