This paper investigates the degradation of polymers during thermal spraying with special reference to the changes in molar mass. A study is carried out on the degradation of polymethylmethacrylate (PMMA) during plasma spraying. The infrared spectroscopy showed that the coating did not lead to any significant chemical reactions. However, the gel permeation chromatography measurement revealed larger changes in the molar mass with a decrease of up to 70% in the average numerical molar mass of the PMMA. The results show that increasing the arc power resulted in a substantial increase in degradation. Because of the extremely low thermal conductivity of polymers, the magnitude of these effects becomes even worse. The results indicate that it is important to consider molar mass measurements along with spectroscopic analysis when characterizing thermally sprayed polymer coatings. Paper includes a German-language abstract.