Living radical polymerization: Use of an excess of nitroxide as a rate moderator

The kinetics of the living radical polymerization of n-butyl acrylate (BuA) in the presence of an excess of N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (DEPN) as a rate moderator has been studied in the temperature range 115-125 degreesC. The equilibrium rate constant K = k(d)/k(c), between dormant and active chains was determined experimentally from the slope of ln([BuA](0)}/[BuA]) vs time. It obeys the following Arrhenius relation: K = 4.93 x 10(5) exp(-119.3 kJ mol(-1)/RT), i.e., K = 1.09 x 10(-10) mol L-1 at 125 degreesC. Some straightforward analytical kinetic equations that only depend on the excess of DEPN as the experimental parameter were established. These equations were successfully applied to simulate the DEPN-mediated polymerization of n-butyl acrylate initiated by either a styryl-DEPN alkoxyamine or an AIBN/DEPN bicomponent system. Last, the slow degradation of DEPN was considered in order to account for the upward deviation of the kinetics when a great excess of DEPN was used.