Dodecylbenzenesulfonic acid, DDBSA, was chosen as a new rate-accelerating additive for 2,2,6,6,-teramethyl-1-piperidinyloxy (TEMPO)-mediated stable free radical polymerization of n-butyl acrylate (n-BA) monomers with 2,2'-azobisisobutyronitrile (AIBN). It was found that the number-average molecular weight of polymers could reach about ten thousand with a narrow polydispersity index (PDI) of 1.4 in a few minutes, which was faster than other systems reported previously. But, at higher conversion, the molecular weight distribution of polymers became broad, and a bimodal distribution occurred. The macro-initiators isolated from the former polymers with narrow PDI could be extended by polymerization with monomers by the addition of DDBSA. Furthermore, a proposed kinetic model demonstrated that the decay of the concentration of DDBSA would reduce the living polymer concentration and retard the growth of the polymers, which could be further propagated by the supplement of DDBSA. (C) 2004 Wiley Periodicals, Inc.