Photoreduction of CHCl in Aqueous SPEEK/HCO Solutions Involving Free Radicals.

Exposure of sulfonated poly(ether etherketone), SPEEK, in aqueous solutions to 350 nm photons induced reduction of CHCl to CHCl and chloride ions in the presence of HCOH/HCO buffers or poly(vinyl alcohol), PVA. The kinetics of the SPEEK-sensitized photoreaction was characterized by quantum yields of halide ion formation, ϕ(Cl), evaluated from in situ determinations of [Cl]. Particularly efficient reductions took place when formate buffers served as H atom donors in the absence of air and with excess CHCl. The dependence of ϕ(Cl) on the inverse square root of the light intensity together with postirradiation formation of Cl in the dark indicated that the CHCl photoreduction occurred via a chain process. EPR determinations identified the α-hydroxy radical of SPEEK and CHCl as chain carriers. Most of the kinetic findings were rationalized in terms of a free radical mechanism where dimerizations of the radicals acted as termination steps. Photoreduction of CHCl was also detected in the presence of air albeit with lower quantum efficiencies. Observations made during postirradiation experiments indicated that a chain process was also operative under such conditions.