Effect of temperature on the equilibrium of reversible inhibition in nitroxide-mediated radical polymerization of styrene

The effect of temperature on the kinetics of benzoyl peroxide-initiated pseudo-living radical polymerization of styrene carried out in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radicals was studied by isothermal calorimetry and ESR spectroscopy. It was shown that in the 110-140°C range, the basic process proceeds by the reversible inhibition mechanism at an almost constant rate on a background of the steady-state concentration of TEMPO increasing with temperature. The temperature dependence of the equilibrium constant for the reaction of reversible inhibition was determined, and the effective activation energy of polymerization and the activation energy of reinitiation were found to be 82 ± 4 and 140 ± 15 kJ/mol, respectively.