Investigating Temporal Control in Photoinduced AtomTransfer Radical Polymerization

External\nregulation of controlled polymerizations allows for controlling\nthe kinetics of the polymerization and gaining spatial or temporal\ncontrol over polymer growth. In photoinduced atom transfer radical\npolymerization (ATRP), light irradiation (re)­generates the copper\ncatalyst to switch the polymerization on. However, removing the light\ndoes not immediately inactivate the catalyst, nor does the rate of\npolymerization become zero as chains may grow in the dark because\nof continued activation by the residual activator catalyst or regeneration\nof the Cu catalyst in the dark. In this paper, the effect of polymerization\ncomponents on photoinduced ATRP was investigated to understand the\ninterplay of temporal control and light switching. Kinetics of polymerization\nwere monitored using in situ NMR as well as under conventional batch\nconditions. The extent of the polymerization in the dark depended\non the activity of the Cu catalyst, which was regulated by the nature\nof the ligand and reaction medium. For highly active catalysts, the\nequilibrium concentration of the L/CuI activator is very\nlow, and it was rapidly depleted by radical termination reactions,\nyielding temporal control which closely matched the switching of light\nto on or off. Decreasing the activity of the Cu catalyst increased\nthe equilibrium concentration of the activator, leading to significant\nchain growth in the dark.