Reversible addition-fragmentation chain transfer (RAFT) was applied to the copolymerization of styrene and maleic anhydride. The product had a low polydispersity and a predetermined molar mass. Novel, well-defined polyolefin-based block copolymers were prepared with a macromolecular RAFT agent prepared from a commercially available polyolefin (Kraton L-1203). The second block consisted of either polystyrene or poly(styrene-co-maleic anhydride). Furthermore, the colored, labile di-thioester moiety in the product of the RAFT polymerizations could be removed from the polymer chain by UV irradiation.