We characterized the kinetics of a photo cleavable o-nitrobenzyl (ONB)-modified poly(methyl acrylate) in solution and in film. Using atom transfer radical polymerization, a single photolabile ONB group was incorporated into the center of the polymer chain, resulting in a clearly defined photoresponse. The photocleavage behavior was characterized in three difference solvents and in film, and it was fit to an exponential model. The dependence of the reaction rate constants and quantum efficiency on the interaction :parameter between the solvent and the polymer (chi(12)) and the molecular weight was investigated. Interestingly, as chi(12) decreased, the reaction rate increased and the quantum efficiency increased.