Kinetic study of the nitroxide-mediated controlled free-radical polymerization of n-butyl acrylate in aqueous miniemulsions

The controlled free-radical homopolymerization of n-butyl acrylate was studied in aqueous miniemulsions at 112 and 125 degreesC with a low molar mass alkoxyamine unimolecular initiator and an acyclic P-phosphonylated nitroxide mediator, N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide, also called SG1. The polymerizations led to stable latices with 20 wt % solids and were obtained with neither coagulation during synthesis nor destabilization over time. However, in contrast to latices obtained via classical free-radical polymerization, the average particle size of the final latices was large, with broad particle size distributions. The initial [SG1](O)/[alkoxy-amine](O) molar ratio was shown to control the rate of polymerization. The fraction of SG1 released upon macroradical self-termination was small with respect to the initial alkoxyamine concentration, indicating a very low fraction of dead chains. Average molar masses were controlled by the initial concentration of alkoxyamine and increased linearly with monomer conversion. The molar mass distribution was narrow, depending on the initial concentration of free nitroxide in the system. The initiator efficiency was lower than 1 at 112 degreesC but was very significantly improved when either a macroinitiator was used at 112 degreesC or the polymerization temperature was raised to 125 degreesC. (C) 2002 Wiley Periodicals, Inc.