Fillers such as silica are often added to rubber to improve performance in commercial applications. The use of silica in rubber compounds improves important compound properties such as tensile strength and cut growth resistance. A difficulty with using silica as a filler is the high energy of mixing due to both poor rubber-filler and strong filler-filler interactions. Improved compatibility between the silica and rubber can be achieved using admicellar polymerization to modify the silica surface. Previously, this process had been performed only in batch reactors, which are usually not appropriate for industrial applications, especially for providing a consistent product. In this work, a continuous stirred-tank reactor (CSTR) for admicellar polymerization was developed. The feed was comprised of precipitated silica, cetyltrimethylammonium bromide (CTAB) cationic surfactant, styrene and isoprene comonomers, and 2,2'-azobisisobutyronitrile initiator. The results showed that the modified silica reduced T-90 cure times and improved modulus, abrasion resistance, and compression set. The optimum conditions for surface modification of silica by the admicellar polymerization process were 5 g comonomer loading per kg silica and a 30-min reaction time. In comparison with the modified silica using a batch process, the modified silica obtained from the CSTR process was found to be superior in the performance of rubber compound. (c) 2005 Published by Elsevier B.V.