title: Radical-triplet pair interactions as probes of long-range polymer motion in solution.
abstract: Radical-triplet pair interactions are used to investigate the dynamics of acrylic polymers in dilute solution. Methyl methacrylate was randomly copolymerized with a small amount of an amine-containing monomer to create the polymers. The amine subunits were then oxidized to nitroxide moieties (stable free radicals). Using time-resolved electron paramagnetic resonance (TREPR) spectroscopy on the sub-microsecond time scale, competition is observed between two deactivation processes of the ester side chain photoexcited triplet state: (1) Norrish I α-cleavage, leading to a 21-line main chain polymeric free radical TREPR spectrum with emissive triplet mechanism spin polarization, and (2) spin polarization transfer or quenching by a nearby stable nitroxide radical, which gives a 3-line spectrum exhibiting emissive radical-triplet pair spin polarization. The main chain polymer radical signal dominates the TREPR spectrum if the probability of radical-triplet pair encounters is low. These competing reactions show a strong dependence on nitroxide incorporation (mol %), temperature, solvent, and acrylic polymer ester side chain structure. A comparison of steady state EPR and TREPR signals from inter- vs intramolecular processes clearly demonstrates the influence of polymer chain dynamics on the observed phenomena.
authors: Department of Chemistry Caudill Laboratories, CB#3290, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors: Sooyeon
authors: S
authors: Sim
authors: Malcolm D E
authors: MD
authors: Forbes