Constitutive equations are derived for the kinetics of physical aging in polymeric glasses. A polymer is treated as an ensemble of cooperatively re-arranging regions (CRR) which relax at random times as they are thermally agitated. According to the coarsening concept, structural recovery is modeled as fragmentation and aggregation of relaxing regions, whose rates are determined by volumes of appropriate CRRs. To verify the model, experimental data in dynamic shear tests for two kinds of poly(vinyl acetate) are compared with results of numerical simulation. Fair agreement is demonstrated between observations and predictions of the model.