Controlled atom-transfer radical polymerization and ring-opening polymerization methods are used for the first time to synthesize symmetric pentablock copolymers with a central block, which is a polymer brush with the polyimide backbone and poly(methyl methacrylate) side chains, and outer linear block copolymers of poly(e-caprolactone) with poly(methyl methacrylate). The chemical structure of the polymers is studied by 1H NMR spectroscopy. The molecular weight characteristics of the synthesized pentablock copolymers are determined by multidetector size exclusion liquid chromatography. It is shown that these characteristics are in good agreement with the absolute molecular weights obtained by sedimentation-diffusion analysis.