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 (PRFMAs) 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 PRFMAs 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 PRFMAs 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 PRFMAs may be developed further to synthesize radiation-sensitive materials working under e-beam and extreme ultraviolet (lambda = 13.5 nm) lithography conditions for advanced patterning applications. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2672-2680