Pentafluoropyridine,
a potentially useful precursor in organofluorine
methodology, undergoes selective substitution of a fluorine with a
phenoxide at the site para to the nitrogen. Subsequent
aryloxide substitutions can be accomplished at the ortho-positions with aryloxide groups containing various functional groups para to the phenoxide oxygen. During this phase of the reaction,
“reverse reactions” involving substitutions of the original para substituent with a free fluoride or with another aryloxide
moiety are observed with a frequency that depends on the functional
group para to the oxygen on the aryloxide. Herein,
we provide a theoretical explanation of these observations through
use of density functional theory.
A new
polycyanurate network exhibiting extremely low moisture uptake
has been produced via the treatment of perfluorocyclobutane-containing
Bisphenol T with cyanogen bromide and subsequent thermal cyclotrimerization.
The water uptake, at 0.56 ± 0.10% after immersion in water at
85 °C for 96 h, represents some of the most promising moisture
resistance observed to date in polycyanurate networks. This excellent
performance derives from a near optimal value of the glass transition
at 190 °C at full cure. Superior dielectric loss characteristics
compared to commercial polycyanurate networks based on Bisphenol E
were also observed. Polycyanurate networks derived from this new monomer
appear particularly well-suited for applications such as radomes and
spacecrafts where polycyanurates are already widely recognized as
providing outstanding properties.
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