Living Radical Polymerization: Use of an Excess of Nitroxide as a Rate Moderator

Abstract

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 °C. The equilibrium rate constant K = kd/kc 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 × 105 exp(−119.3 kJ mol-1/RT), i.e., K = 1.09 × 10-10 mol L-1 at 125 °C. 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.