Bound rubber in a filled rubber compound is formed by physical adsorption and chemisorption between the rubber and the filler. Styrene-butadiene rubber (SBR) is composed of four components of styrene, cis-1,4, trans-1,4-, and 1,2-units. Filler-polymer interactions in both silica and carbon black-filled SBR compounds were studied by analyzing microstructures of the bound rubbers with pyrolysis-gas chromatography. Differences in the filler-polymer interactions of the styrene, cis-1,4-, trans-1,4-, and 1,2-units were investigated. The filler-polymer interactions of the butadiene units were found to be stronger than that of the styrene unit. The interactions of the cis-1,4-and trans-1,4-units were stronger with carbon black than with silica, whereas the 1,2-unit interacted more strongly with silica than with carbon black. (C) 2001 John Wiley & Sons, Inc.