Fourier transform infrared spectroscopic study of thermal degradation in films of poly(etheretherketone)

Fourier transform infrared (FT-IR) spectroscopy was used to study the reactions which occur upon thermal degradation of films of poly(etheretherketone), or PEEK. Samples were exposed to temperatures in the range 400–485°C in both air and nitrogen atmospheres, and spectra were measured in both transmission and attenuated total reflection (ATR). The thermal degradation produces new carbonyl species, and the rate of growth of their IR peaks was used to determine activation energies for the reactions which produce them. In an inert atmosphere, the degradation involves a pyrolytic-type mechanism which produces a new carbonyl species absorbing in the IR at 1711 cm−1, possibly a fluorenone-type structure. The activation energy for this process is 236 kJ mol−1. In an oxidizing atmosphere, the same species is produced but at a faster rate, and the apparent activation energy is 211 kJ mol−1. In addition there is a second mechanism which requires the participation of oxygen and produces a species absorbing at 1739 cm−1, possibly ester groups. The activation energy for this reaction is 116 kJ mol−1. Because of the time required for oxygen to diffuse into the polymer, oxidative degradation is more pronounced at the surface, especially at higher temperatures. Thus ATR gives a more reliable value of the activation energies than transmission measurements on the bulk film.