The design of a novel difunctional chain transfer agent (CTA) based on the propagating core (R group) approach is detailed. Successful synthesis of ABA block copolymers of poly(butyl methacrylate)-b-poly(methyl methacrylate)-b-poly(butyl methacrylate) and poly(butyl acrylate)-b-poly(methyl methacrylate)-b-poly(butyl acrylate) with targeted molecular weight and polydisperity indices in the range 1.2-1.4 is reported. The effect of free radical initiator concentration with respect to CTA concentration on block efficiency is investigated and lower concentrations were found to increase reaction time, but significantly reduce termination reactions. The consequence of difunctionality on homo and block extension polymerizations is discussed, with the polymerization of methyl and butyl methacrylate being more controlled than butyl acrylate.