A series of 19 p-substituted aromatic trifluorovinyl ether compounds were prepared from versatile intermediate p-Br-C(6)H(4)-O-CF=CF(2) and underwent thermal radical mediated cyclodimerization to new difunctional compounds containing the 1,2-disubstituted perfluorocyclobutyl (PFCB) linkage. The synthetic scope demonstrates the functional group transformation tolerance of the fluorovinyl ether, and the dimers are useful as monomers for traditional step-growth polymerization methods. (19)F NMR spectra confirmed that p-substitution affects the trifluorovinyl ether group chemical shifts. The first kinetic studies and substituent effects on thermal cyclodimerization were performed, and the results indicated that electron-withdrawing groups slow the rate of cyclodimerization. The data were further analyzed using the Hammett equation, and reaction constants (rho) of -0.46 at 120 degrees C and -0.59 at 130 degrees C were calculated. This study presents the first liner free energy relationship reported for the cyclodimerization of aromatic trifluorovinyl ethers to PFCB compounds.
Hexa-peri-hexabenzocoronene (HBC) derivatives possess many interesting properties ranging from liquid crystallinity, to hole transport, to variable emission behavior, yet are plagued by insolubility and general accessibility of polymerizable substituents. The first synthesis of trifluorovinyl ether-substituted hexabenzocoronene and its polymerization to perfluorocyclobutyl (PFCB) polymers and copolymers is shown. Unlike hydrocarbon ethers, fluoro vinyl ethers are stable under HBC oxidation conditions. Discrete HBC units in PFCB polymers provide access to potentially processable HBC optical materials.
A novel class of phenylphosphine oxide (PPO) containing perfluorocyclobutyl (PFCB)
polymers has been developed for potential use as multifunctional materials in space environments. The
reaction of p-BrArOCFCF2 (for Ar = phenyl and biphenyl) with tert-butyllithium affords the lithium
reagent smoothly below −20 °C. Subsequent substitution with phenylphosphonic dichloride provides the
first bis(trifluorovinyl ether) monomers containing the PPO group. Polymerization proceeds thermally
above 150 °C to give polymers that exhibit glass transition temperatures of 169 and 224 °C, respectively,
and catastrophic weight loss by TGA in N2 and air above 450 °C (10 °C/min). Copolymerization with
bis(4,4‘-trifluorovinyloxy)biphenyl affords film-forming transparent thermoplastic copolymers with high
T
g (>140 °C) and good thermal stability (>450 °C). Initial evaluations with ground-based simulation of
atomic oxygen (AO) rich space environments indicate that the PPO group imparts significant space
durability to PFCB polymers.
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