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. A simple kinetic model of the polymerization can be generated by adding the elementary reactions of comproportionation, disproportionation and activation by copper(0) to the standard reactions of ATRP. Observed features such as �-order dependence on the copper surface area and loss of control in strongly comproportionating solvents arise naturally from this model. An interesting feature of the polymerization is that the copper(I) concentration is low and nearly constant, while the concentration of copper(II) species increases as a function of the number of dead polymer chains. Measurement of the rate of generation of copper(II) thus allows measurement of the rate of termination at any point in the reaction. As the chain length is relatively narrowly distributed, and increases as a function of conversion, this provides a means of probing the chain-length dependence of the rate of bimolecular termination. 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. The rate of activation of dormant polymer chains by copper(0) shows similar chain length dependence.

Chain-length-dependent activation and termination in SET LRP/SARA ATRP

248th National Meeting (2014)

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