AbstractSummary: Macromonomers have been prepared by polymerization of acrylic acid (AA) and tert‐butyl acrylate (tBA) in the presence of the addition‐fragmentation chain transfer (AFCT) agents, ethyl α‐(bromomethyl)acrylate (EBMA) and tert‐butyl α‐(bromomethyl)acrylate (BBMA). Chain transfer constants of 1.25 (EBMA) and 1.14 (BBMA) in the AA polymerization, and 2.42 (EBMA) and 1.75 (BBMA) in the tBA polymerization were obtained. The reduction in molecular weight with increasing concentration of AFCT agent and efficient introduction of 2‐carbalkoxy‐2‐propenyl ω‐end group was indicative of macromonomer formation. Polymerizations were retarded with increasing concentrations of AFCT agent and increases in the absolute concentration of EBMA slowed down the polymerization of AA but not tBA. The difference between EBMA and BBMA was less significant with tBA; more efficient macromonomer synthesis was indicated by less retardation and greater double bond retention at higher conversions. Copolymerizations of poly(AA) and poly(tBA) macromonomers with styrene indicated that the former was more reactive towards the St propagating radical. The results are rationalized in terms of the steric hindrance imposed by the tert‐butyl group. Poly(tBA) macromonomer was successfully hydrolyzed to give an alternative route to the poly(AA) macromonomer.Reaction mechanism for macromonomer synthesis using AFCT.magnified imageReaction mechanism for macromonomer synthesis using AFCT.