N‐tert‐Butyl‐1‐diethylphosphono‐2,2‐dimethylpropyl nitroxide as counter radical in the controlled free radical polymerization of styrene: kinetic aspects

The controlled free radical polymerization of styrene with N‐tert‐butyl‐1‐diethylphosphono‐2,2‐dimethylpropyl nitroxide (DEPN) as counter radical was studied. Polymerizations were performed in bulk, with a DEPN‐capped polystyryl as alkoxyamine initiator, in the presence of an excess of DEPN nitroxyl free radicals. Kinetics of the polymerization were followed at 115°C, 125°C and 130°C. The equilibrium rate constant K = k_d/k_c of exchange between dormant and active species was determined experimentally from the slope of Ln(styrene]₀/styrene]) versus time. The obtained Arrhenius relation was the following: K (mol·L^–1) = 1.45×10⁷exp (–113.5 kJ·mol^–1/RT), i.e., K = 1.9×10^–8 mol·L^–1 at 125°C. This result is consistent with a much faster polymerization of styrene with DEPN than with Tempo as nitroxyl counter radical (K = 2.1×10^–11 mol·L^–1 at 125°C determined previously by Fukuda).