An important effect in the degradation of solubilized polymers is the influence of the solvent on the degradation rate. Depending on the particular polymer, hydrogen (H-)donors can increase, decrease, or have no effect on degradation rate. We experimentally investigated the effect of H-donor 6-hydroxy tetralin on polystyrene degradation. In this case the rate decreases with increasing H-donor concentration. Mathematical expressions for the degradation rate parameters were obtained by applying continuous-distribution kinetics to the MWD of the reacting polymer. A model was developed for radical mechanisms based on the Rice-Herzfeld chain-reaction concept with the elementary steps of initiation, depropagation, H-abstraction and termination. The model accounted for the varied effects of the H-donor on polymer degradation.