Polystyrene-block-polybutadiene-block-poly(glycidyl methacrylate) (SBG) and polystyreneblock-polybutadiene-block-poly(methyl methacrylate)-block-poly(glycidyl methacrylate) copolymers (SBMG) were synthesized by sequential living anionic polymerization in tetrahydrofuran (THF). SBMG copolymers were used as modifiers for epoxy thermosets based on the diglycidyl ether of bisphenol A (DGEBA). Different techniques including differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and optical cloud point measurements have been used to demonstrate the advantage of having a reactive copolymer to finely tune and control the morphology of nanostructured materials. The FT-III and DSC studies were used to follow both the kinetics of reaction of the reactive block G with the epoxy-amine system and of cross-linking of the epoxy-amine system. They give an interesting insight into the problem of factors governing the expulsion of the methacrylic block out of the epoxy-amine phase during network formation. Morphological characteristics revealed by TEM appear to be closely related to the optical properties of these composites.