Inherent Microporosity and Photostability of Fluoroacrylic Polymer Films Studied by Electron Paramagnetic Resonance of Nitroxide Spin Probes

Abstract

Efficient and straightforward methods for characterization of polymers with inherent microporosity are demanded in their targeted design for particular applications. Among critical parameters to be obtained are the size of the pores and polymer stability against photoirradiation. Herewith, we demonstrate the efficiency of electron paramagnetic resonance (EPR) spectroscopy applied to this task. We use stable nitroxide radicals (2,2,6,6-tetramethylpyperidine-1-oxyl) (TEMPO) as reporter spin probes for EPR and investigate a series of perspective polymers with inherent microporosity developed for pressure sensitive paints (PSP), namely, poly(1,1,1,3,3,3-hexafluoroisopropylmethacrylate-co-2,2,3,3,4,4,4-heptafluorobutylmethacrylate) (FIB), its two modifications poly(1,1,1,3,3,3-hexafluoroisopropylmethacrylate-co-2,2,3,3,4,4,4-heptafluorobutylmethacrylate-co-1-(4-(4-chloro-2,3,5,6-tetrafluorophenyl)piperazin-1-yl)prop-2-en-1-one) (NS4) and poly(1,1,1,3,3,3-hexafluoroisopropylmethacrylate-co-2,2,3,3,4,4,4-heptafluorobutylmethacrylate-co-1-(4-(4-tert-butylphenylsulfonyl)piperazin-1-yl)prop-2-en-1-one) (NS5), as well as poly(1-trimethylsilyl-1-propyne) (PTMSP) and poly(1,1,2,2-perfluorooctylmethacrylate) (PFOMA). Nitroxides were incorporated into the pores of the polymers post-synthetically via a gas-phase sorption, and the mobility of nitroxides tracked by EPR yielded information on the pore sizes and polymer degradation under ultraviolet light. The conclusions obtained by EPR have been supported by a variety of other techniques, thus demonstrating EPR to be a very convenient tool for express analysis of porous polymers.