Investigation of degradation pathways of poly(semiperfluoroalkyl methacrylate) thin films induced by electron-beam irradiation

In this article, we report the results of high-energy electron beam (e-beam) irradiation of polymer thin films made of poly(semiperfluoroalkyl methacrylate)s (PR_FMAs) and propose plausible chemical reactions that may cause their solubility to change in fluorous liquids. It was observed that the polymer films were converted to a more soluble state under low exposure doses of e-beam, possibly due to main-chain scission. However, the films became insoluble with higher doses of e-beam. Three hypotheses were proposed to explain the reduction in solubility, and we used data from Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, mass spectrometry (MS), and nanoindentation to eliminate the less probable hypotheses. The results derived from e-beam-irradiated thin films of three PR_FMAs showed that the radical-related Norrish Type I and II pathways may not be the main decomposition routes. The data also suggested that sufficient scission reactions of the perfluorooctyl moieties of PR_FMAs do not occur by e-beam. We therefore assumed that the decrease in solubility of the fluorinated polymers results from intermolecular crosslinking reactions between the free radicals and reactive moieties generated on the perfluorooctyl groups by the e-beam. The unique imaging mechanism of PR_FMAs may be developed further to synthesize radiation-sensitive materials working under e-beam and extreme ultraviolet (λ = 13.5 nm) lithography conditions for advanced patterning applications.