Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to study the pyrolysis of polyimide (Kapton<sup>®</sup>). The samples were prepared in a KBr matrix, which did not show pronounced interferences, such as increased emissivity, during the measurements. The pyrolysis of Kapton<sup>®</sup> reveals pronounced differences from laser-induced (UV) decomposition. The polyimide system decomposes thermally in distinct steps, i.e., first the imide ring, without elimination of the carbonyl groups, followed by the aromatic system and then the carbonyl groups. Several intermediates, such as nitriles and alkynes, are identified. The quantitative analysis of the spectra suggests that Kapton<sup>®</sup> decomposes in two steps, i.e., as a growing particle with shrinking core followed by a shrinking particle. The growing particle with shrinking core is the nonreacted polymer as core and a polyamic structure as the growing part, while the shrinking particle is the complete pyrolysis of the polymer. The activation energies for these two steps were determined. The reaction rate appears to be diffusion controlled at low temperatures and surface reaction controlled at higher temperatures.
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