Single Electron Transfer Living Radical Polymerization (SET LRP), also known as Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization (SARA ATRP), is a form of controlled radical polymerization which is carried out in the presence of copper metal, a ligand (e.g. Me6tren), and an activated alkyl halide initiator. The mechanism of the polymerization is contested, with debate focusing in part on the relative importance of comproportionation and disproportionation of copper species. We present here a simple method for the determination of two key rate constants: activation of alkyl halides by copper metal (ka0) and comproportionation of copper(0) and copper(II) (kcomp). This is carried out by following the consumption of an alkyl halide initiator in the presence of copper metal , ligand, and a radical trap such as N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide.The elementary reactions of comproportionation, disproportionation and activation by copper(0) can be added to the standard reactions of ATRP to form a kinetic model of the polymerization. Observed features such as �-order dependence on the copper surface area and loss of control in strongly comproportionating solvents arise naturally from this model. Finally, chain length dependence of termination kinetics can be probed by observing the rate of generation of copper(II) species during the reaction. We show that addition of copper(II) halide, while narrowing the molecular weight distribution, can cause a reduction in chain-end functionality due to faster termination of shorter chains.

Comproportionation, activation, and termination in SET LRP/SARA ATRP

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.