The potential of Initiators for Continuous Activator Regeneration Atom Transfer Radical Polymerization (ICAR ATRP) to determine reliable Arrhenius parameters for ATRP activation/deactivation of macrospecies is illustrated using styrene as monomer and CuBr2/TPMA (TPMA: tris­(2-pyridylmethyl)­amine) as deactivator. Regression is based on an extensive set of experimental data limited to conversions below 0.50 to avoid the interference of diffusional limitations on the activation/deactivation process and recorded at temperatures below 90 °C to avoid the influence of thermal self-initiation. Diffusional limitations on termination are accounted for based on literature data. The activation energy for the activation and deactivation reaction involving macrospecies are respectively 29 and 1.7 kJ mol–1. The corresponding pre-exponentional factors are 6.9 × 105 and 1.8 × 107 L mol–1 s–1. At 70 °C, the corresponding rate coefficients amount to 2.2 × 10 and 9.9 × 106 L mol–1 s–1, confirming the relatively high activity of CuBr/TPMA as ATRP catalyst.