The results are reported of the compositional fractionation of poly(methyl methacrylate)-graft-polydimethylsiloxane (PMMA-graft-PDMS) by high-performance liquid chromatography (h.p.l.c.) of reversed-phase adsorption mode. Graft copolymers with different compositions were prepared by the radical copolymerization of PDMS macromonomer with MMA, using azobisisobutyronitrile as the initiator in benzene at 60 degrees C. The gradient h.p.l.c. measurements were made using a prepacked column of octyl-modified silica gel, with tetrahydrofuran and acetonitrile as eluents. Detection was performed by an evaporative light-scattering detector. The PMMA-graft-PDMS samples were eluted from the components of higher PMMS contents to those of lower PMMA contents, according to reversed-phase adsorption. The present graft copolymers were separated according to their chemical compositions.