By dynamic calorimetry the temperature dependence of heat capacity for two-dimensional (2D) polymerized tetragonal phase of C-60 has been determined over the 300-650 K range at standard pressure mainly with an uncertainty +/-1.5%. In the range 490-550 K, an irreversible endothermic transition of the phase, caused by the depolymerization of the polymer, has been found and characterized. Based on the experimental data obtained and literature information, the thermodynamic functions of 2D polymerized tetragonal phase of C-60, namely, the heat capacity C(p)degrees(T), enthalpy Hdegrees(T) - Hdegrees(0), entropy Sdegrees(T), and Gibbs function Gdegrees(T) - Hdegrees(0), have been calculated over the range from T --> 0 to 490 K. From 150 to 330 K in an adiabatic vacuum calorimeter and between 330 and 650 K in a dynamic calorimeter the thermodynamic properties of the depolymerization products have been examined and compared with the corresponding data for the monomeric phase C-60. (C) 2003 Elsevier B.V. All rights reserved.