The bulk physical aging behavior of cross-linked polystyrene (PS) is directly compared to that of its linear precursor polystyrene-co-vinylbenzocyclobutene (PS-VBCB) with 8.5 or 12.5 mol% VBCB content. The VBCB units incorporated into a linear PS precursor cross-link with one another upon annealing at 250 degrees C. Physical aging rates of bulk PS-VBCB films before and after cross-linking are characterized using ellipsometry by monitoring the decrease in thickness during isothermal annealing at a specific aging temperature (T-a) below the glass transition temperature (T-g). Physical aging rates show strong dependences on T-a values, with neat PS, linear PS-VBCB precursors with 8.5 or 12.5 mol% VBCB, and cross-linked PS with 8.5 mol% VBCB exhibiting maxima at T-a-T-g = -40 to -30 degrees C. In contrast, cross-linked PS with 12.5 mol% VBCB exhibits a maximum aging rate at T-a -T-g = -65 to -45 degrees C. The distribution of T-a-dependent aging rates broadens in cross-linked PS samples compared to linear precursors, which is correlated with increased T-g breadth or heterogeneity after cross-linking. Comparisons of aging rates of cross-linked PS with linear precursors demonstrate that cross-linking can lead to an increased, decreased, or unchanged aging rate depending on the values of T-a and T-a-T-g: e.g., when T-a -T-g > -60 degrees C, both cross-linked PS samples have a lower aging rate compared to their linear precursors at the same T-a-T-g whereas the cross-linked PS exhibits a similar or even greater aging rate compared to the linear precursor when T-a-T-g < -60 degrees C. These results help to reconcile previous seemingly contradictory observations regarding effects of cross-linking on physical aging rates. To the best of our knowledge, crosslinking induced enhancement of physical aging rates of cross-linked polymers relative to their linear precursors at the same T-a-T-g value is being reported for the first time here. (C) 2017 Elsevier Ltd. All rights reserved.