L-PDCPD, obtained with catalysts based on a tungsten complex and allylsilanes has good thermal stability. TGA measurements, in air, show that the first weight losses begin around 350°C. The influence of cocatalyst, macromolecular chain defects, and fast electrons irradiation on the thermal stability of L-PDCPD is presented. The thermal stability of L-PDCPD depends to a certain extent on the type of cocatalysts used in polymerization. Branching of