Kinetics of cap separation in nitroxide-regulated "living" free radical polymerization: Application of a novel methodology involving a prefluorescentnitroxide switch

A novel approach employing a prefluoreseent paramagnetic sensor has been em ployed to determine the absolute kinetics for end-cap cleavage in TEMPO-cap ped polystyrene obtained by "living" free radical polymerization. This new methodology takes advantage of the suppression of coumarin fluorescence whe n this chromophore is tethered to a paramagnetic nitroxide. This coumarin-n itroxide is an excellent free radical trap for carbon-centered radicals; up on radical trapping, the. resulting diamagnetic alkoxyamine is strongly flu orescent. Thus, fluorescence buildup is a direct measure of free radical fo rmation and can be employed to quantify their formation or to study their k inetics. Studies of the temperature dependence of the process can be employ ed to determine activation parameters and bond dissociation energies. This simple technique can be employed to study the dynamics in the actual polyme r systems, overcoming the frequent need to resort to model compounds.