1 research outputs found
Continuous Wave and Time-Resolved Electron Paramagnetic Resonance Study of Photoinduced Radicals in Fluoroacrylic Porous Polymer Films
Fluoroacrylic polymers with inherent
micro/nanoporosity are promising
media for incorporation of fluorescent molecules and following application
as pressure-sensitive paints (PSPs), and UV photostability of PSPs
is critically important for their long-term performance. Although
photodegradation mechanisms of fluoroacrylic polymers have been studied
previously in solutions, they have never been addressed in practically
relevant for PSPs solid-state porous films. In this work we combined
continuous wave (CW) and time-resolved (TR) electron paramagnetic
resonance (EPR) to study UV photodegradation of thin porous films
of a few representative fluoroacrylic polymers. Different types of
spectra were detected using CW and TR EPR and assigned to the species
formed on the inner surface of the pores and in the bulk of the polymer,
respectively. The radical pairs formed in the bulk are short-lived,
as is evidenced by TR EPR, and most likely recombine back to the initial
polymer. On the contrary, the radicals formed on the surface of the
pores are metastable in the absence of oxygen; they can be studied
by CW EPR and clearly assigned to the radicals of type ·CÂ(CH<sub>3</sub>)ÂCH<sub>2</sub>– (so-called propagating radicals) formed
via the cleavage of the C–C bond of the ester side chains and
consecutive β-scission. Remarkably, their CW EPR spectra closely
resemble solution-state spectra, indicating that these radicals are
localized in the pores where the mobility of methyl and methylene
protons is not suppressed. Thus, based on complementary results of
CW and TR EPR, we conclude that UV photodegradation of porous fluoroacrylic
polymer films mainly occurs on the inner surface of the pores, which
needs to be considered in future development of this type PSPs