The highest accessible molecular weight of the living product in controlled/living radical polymerizations (CLRPs) is determined by the constant of chain transfer to monomer reaction. Thus, the highest molecular weight of living polystyrene had been believed around 100 kg/mol in CLRPs. In our previous report (Yan, K; Gao, X.; Luo, Y. Well-Defined High Molecular Weight Polystyrene with High Rates and High Livingness Synthesized via Two-Stage RAFT Emulsion Polymerization. Macromol. Rapid Commun. 2015, 36 (13), 1277-1282), we surprisingly found that the livingness of polystyrene of 550 kg/mol could be up to 90% in RAFT emulsion polymerization. Herein, we experimentally measure the constant of chain transfer to monomer reaction in RAFT emulsion polymerization of styrene at various temperatures from 60-80 degrees C. Very interestingly, it is found that the constant of chain transfer to monomer reaction should be only about one-third of that of the corresponding conventional radical polymerization. From the derived Arrhenius equation, it is supported that the fast competitive RAFT reactions might significantly decrease the collision frequency for chain transfer to monomer reactions.