The dependence of the heat capacity on temperature measured in DSC heating scans after different thermal histories in poly(methyl methacrylate), poly(ethyl methacrylate), and poly(butyl methacrylate) is reported. These results are analyzed with the help of a phenomenological model for the evolution of cofigurational entropy under arbitrary histories. The possibility of obtaining material parameters from the experimental results is discussed. The dependence of the relaxation times in equilibrium conditions on temperature is calculated for the three polymers and compared with the results of the main viscoelastic and dielectric relaxation processes reported in the literature. The width parameter of the Kohlrausch-Williams-Watts relaxation function is also calculated for the three polymers of this series.