The possibility of using differential scanning calorimetry to study the intermolecular reactions in polymer glasses has been tested experimentally. Polystyrene and the styrene-methacrylic acid copolymer have been used to show the effects of the composition (structure), the thermal and mechanical history on the progress of the differential scanning calorimetry (DSC) curve. The respective energy changes (enthalpy differences ΔH) appearing on the curves in the relaxation transition ranges have been evaluated. The results have been compared with the inter- and intra-molecular reaction changes established by IR spectroscopy. The DSC was found to be useable in a quantitative evaluation of the intermolecular reactions taking place in polymer glasses.