The glass transition of thermoplastics of different polydispersity and thermosets of different network structure has been studied by conventional differential scanning calorimetry (DSC) and temperature modulated DSC (TMDSC). The cooling rate dependence of the thermal glass transition temperature T-g measured by DSC, and the frequency dependence of the dynamic glass transition temperature T, measured by TMDSC have been investigated. The relation between the cooling rate and the frequency necessary to achieve the same glass transition temperature has been quantified in terms of a logarithmic difference Delta = log(10)[|q|]-log(10)(omega), where |q| is the absolute value of the cooling rate in K s(-1) and omega is the angular frequency in rad s(-1) necessary to obtain T-g(q) = T-alpha(omega). The values of Delta obtained for various polymers at a modulation period of 120 s (frequency of 8.3 mHz) are between 0.14 and 0.81. These values agree reasonably well with the theoretical prediction [Hutchinson JM, Montserrat S. Thennochim Acta 200 1;377:63 [6]] based on the model of Tool-Narayanaswamy-Moynihan with a distribution of relaxation times. The results are discussed and compared with those obtained by other authors in polymeric and other glass-forming systems. (c) 2005 Elsevier Ltd. All rights reserved.