Fourier transform infrared attenuated total reflectance spectroscopy was used to characterize ultrathin organic polyimide films deposited on silicon using the Langmuir-Blodgett technique. Both the chemistry and the kinetics of conversion from polyamic acid salt to polyimide were elucidated with strong indications of a novel ring structure intermediate. It is concluded that the conversion may be achieved under relatively mild conditions (immersion in methanol, followed by heating to ca. 85-degrees-C), which is likely to be of importance in an industrial context.