Novel surface attachable AIBN type initiators involving mono-/di-/trichlorosilane anchoring groups have been successfully synthesized and grafted onto silica microspheres (average diameter, pore size and surface area arc 5 mu m, 12 nm, and 300 m(2) g(-1) 9 respectively). Graft density Of surfacc-tahered initiators was estimated on the basis of elemental analysis and thermogravimetric measurements giving 0.446, 0.705, and 0.819 group nm(-2) respectively. Owing to the presence of two anchoring groups newly described initiators call attach to the surface through both ends avoiding the fragment-initiated polymerization in the solution that was considered as a main drawback of asymmetric AIBN-type initiators. Surface-initiated radical polymerization of styrene and N-vinyl pyrrolidone has been carried Out in toluene and water solutions respectively, giving polymer-silica hybrids. Immobilized polystyrene chains were detached from the surface then the molecular weight and molecular weight distribution was determined by gel permeation chromatography giving 141200 Da (5.58), 145 700 (5.72) and 149 100 Da (5.94), respectively. The connection between the initiator Structure and average molecular weight of degrafted polymers furthermore the effect of possible radical-radical termination reaction oil the molecular weight is also discussed.