Kinetic studies of the atom transfer radical polymerization (ATRP) of styrene are reported, with the particular aim of determining radical-radical termination rate coefficients (). The reactions are analyzed using the persistent radical effect (PRE) model. Using this model, average radical-radical termination rate coefficients are evaluated. Under appropriate ATRP catalyst concentrations, values of approximately 2 X 10(8) L mol(-1) s(-1) at 110 degreesC in 50 vol % anisole were determined. (C) 2004 Wiley Periodicals, Inc.