The rheological properties of polymer systems determine their deformation behavior and the relationship between stresses, strains and strain rates. We present the results of determining the melting points of solid polymer compounds by the rheological method. Tests were carried out using a rotary rheometer in an oscillating mode. Using the obtained thermomechanical dependences, the experimental data were compared with the values determined by standard analytical (capillary method) and thermal (differential scanning calorimetry) methods. The viscous and elastic behavior of the samples were analyzed using the dependence of the oscillating stress or strain on the angular velocity or frequency. It is shown that the temperature dependences of the storage and loss moduli, as well as the angle of mechanical losses, determine the physical and relaxation transitions in polymers upon their heating. The obtained results can be used in analysis of the effect of conditions of polymer processing on their properties, as well as in optimization of the technological processes of product manufacture and modeling the behavior of materials under operation conditions at the stage of development.