The morphology of poly(styrene-block-butyl methacrylate) (SBMA) copolymer with 42 wt% S was studied by transmission electron microscopy in a selective environment. Micelles with S cores were observed in dilute solutions in 2-propanol, a non-solvent for S and a theta solvent for the BMA blocks. The solvent influence on the final morphology of SBMA films was investigated. Films obtained from solution in tetrahydrofuran had ordered cylindrical structures. When 10% poly(phenylene oxide) (PPO), which has a preferential interaction with the S blocks, was added to the copolymer, the cylinders turned into spheres with PPO cores separated by the swollen S blocks from a BMA matrix. In PPO/SBMA 50/50 blends multilayer vesicles and lamellar structures coexist. For blends with SBMA content lower than 5%, micelles with BMA cores were observed in a PPO matrix.