Novel alpha-cyclobutenyl-containing inimers were used successfully for atom transfer radical polymerization (ATRP) of tert-butyl acrylate and styrene leading to narrow molecular weight alpha-cyclobutenyl-terminated macromonomers (M-n.SEC= 1600-11 500; PDI = 1.06-1.24). The ATRP processes followed first-order kinetics with respect to the monomer concentration. H-1 NMR studies showed that the cyclobutenyl moiety in the initiator is stable during ATRP processes. The bromine chain end of resulting macromonomers has been used successfully for the syntheses of block copolymer-based alpha-cyclobutenyl macromonomers by ATRP. In particular, a range of well-defined polystyrene-b-poly(tert-butyl acrylate) macromonomers with various terminal alpha-cyclobutenyl groups were synthesized through this methodology.