Bis-perfluorocycloalkenyl (PFCA) aryl ether monomers towards a versatile class of semi-fluorinated aryl ether polymers

Article abstract of DOI:10.1016/j.tetlet.2013.04.087

A unique class of perfluorocycloalkenyl (PFCA) aryl ether monomers was synthesized from commercially available perfluorocycloalkenes (PFCAs) and bisphenols in good yields. This facile one pot reaction of perfluorocycloalkenes, namely, octafluorocyclopentene (OFCP), and decafluorocyclohexene (DFCH), with bisphenols occurs at room temperature via an addition-elimination reaction in the presence of a base. The synthesis of PFCA monomers and their condensation with bisphenols lead to perfluorocycloalkenyl (PFCA) aryl ether homopolymers and copolymers with random and/or alternating polymer architectures.

Full text of DOI:10.1016/j.tetlet.2013.04.087

Tetrahedron Letters 54 (2013) 3609–3612
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Bis-perfluorocycloalkenyl (PFCA) aryl ether monomers towards a
versatile class of semi-fluorinated aryl ether polymers
Babloo Sharma a, Donald G. VanDerveer b, Shawna M. Liff c, Dennis W. Smith Jr. a,
⇑
a Department of Chemistry and The Alan G. MacDiarmid NanoTech Institute, The University of Texas, 800 West Campbell Rd., BE 26, Ricahrdson, TX 75080, USA
b Department of Chemistry, Clemson University, Clemson, SC 29631, USA
c Intel Corporation, Chandler, AZ 85226, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A unique class of perfluorocycloalkenyl (PFCA) aryl ether monomers was synthesized from commercially
available perfluorocycloalkenes (PFCAs) and bisphenols in good yields. This facile one pot reaction of per-
fluorocycloalkenes, namely, octafluorocyclopentene (OFCP), and decafluorocyclohexene (DFCH), with
bisphenols occurs at room temperature via an addition–elimination reaction in the presence of a base.
The synthesis of PFCA monomers and their condensation with bisphenols lead to perfluorocycloalkenyl
(PFCA) aryl ether homopolymers and copolymers with random and/or alternating polymer architectures.
Published by Elsevier Ltd.
Received 7 March 2013
Revised 17 April 2013
Accepted 19 April 2013
Available online 27 April 2013
Keywords:
Perfluoro and semifluorinated polymers
Perfluorocycloalkenes
Addition–elimination reaction
Polycondensation
Perfluorinated and semi-fluorinated polymers are continually
sought due to their profound and exclusive properties in applied
chemistry and biochemistry.1–4 Innovative and efficient methods
are highly desired to strategically incorporate fluorine into molecu-
lar architectures with outstanding and specifically designed perfor-
mance. Incorporation of fluorine into polymeric systems results in a
unique combination of properties such as excellent thermal stabil-
ity, chemical inertness, unique surface properties, low refractive in-
dex, low dielectric constant, and low optical loss in telecom
wavelength.1,2,5–10 Such materials are potentially suitable as matri-
ces for non-linear optics (NLO) or electro-optics (EO) applications as
demonstrated by Iacono et al, and many other research groups
including ours with perfluorocyclobutyl (PFCB) aryl ether polymers
and other fluorinated vinylene derived polymers.8–11
the synthesis of bis-perfluorocycloalkenyl (PFCA) aryl ether mono-
mers from perfluorocyclo-olefins, namely, OFCP and DFCH and
bisphenols via an addition–elimination reaction in the presence
of a base (Scheme 1).
Table 1 denotes the bisphenol and PFCA starting materials,
monomers there from (M1–M6), and isolated yield of the conden-
sation reaction. Further, the X-ray crystal structures of M1 (Fig. 2)
and M6 (Fig. S22) were also solved.
With few exceptions such as, fluorinated vinylene derived Tef-
lon, perfluorocyclco-olefins, in general, do not undergo homopoly-
merization via free radical mechanism.36 Recently, we have
F
F
F
F
F
F
F
F
F
F
F
F
F
F
Perfluorocycloalkenes (PFCA) are a general class of compounds
comprising many commercially available perfluorocyclo-olefins
including octafluorocyclopentene (OFCP) and decafluorocyclohex-
ene (DFCH) (Fig. 1). As expected, PFCAs react with various nucleo-
philes including phenoxides,12–15 alkoxide,16–18 organometallic,19–
F
F
F
F
(a)
(b)
Figure 1. Commercially available perfluorocycloalkenes (a) OFCP and (b) DFCH.
21
amines,22–25 thiols,26 azoles27 and phosphonium ylides.28 PFCA
derivatives have thus shown a variety of applications including
photochromic small molecules,29–33 nonlinear optical activity,34
lubricants,21 and etching agents.35 Herein we extend our recently
published initial discovery of perfluorocyclopentenyl (PFCP) aryl
ether polymers5––a new step growth Polycondensation and report
CF2
CF
CF
2 x
2 x
O
x
F
NEt3
DMF
+
OH
HO
R
F
/
R
O
F
F
R =
x = 3 , 4
C(CH3)2
C(CF3)2
⇑
Corresponding author. Tel.: +001 972 883 2915; fax: +001 972 883 2925.
E-mail address: dwsmith@utdallas.edu (D.W. Smith).
Scheme 1. Perfluorocycloalkenyl (PFCA) aryl ether monomer synthesis.
0040-4039/$ - see front matter Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.tetlet.2013.04.087

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B. Sharma et al. / Tetrahedron Letters 54 (2013) 3609–3612
Table 1
allylic product was noticeable in case of DFCH (M3–M6) as evident
Reaction of bisphenols with perfluorocycloalkenes
by three signals with identical molecular weight in the GC–MS
spectra (Fig. S23). Allyl substitution was not observed in case of
OFCP (M1–M3) as evidenced by NMR and GC–MS. The presence
of allylic products for M4–M6 also explains the unaccounted sig-
nals in the 1H, 19F and 13C NMR (Figs. 3 and S13–S20). Interestingly,
there were no other addition products, as has previously been
reported with fluorinated arylene vinylene ether (FAVE)
polymers.37,38
Entry
Bisphenol
PFCA
Yielda (%)
M1
M2
M3
M4
M5
M6
Biphenol
OFCP
OFCP
OFCP
DFCH
DFCH
DFCH
76
71
72
69
63
62
Bisphenol-A
Bisphenol-AF
Biphenol
Bisphenol-A
Bisphenol-AF
a
13Carbon (19F-coupled) NMR has been proved to be a very help-
ful technique to determine structural properties of M1–M6. 19Fluo-
rine coupled 13Carbon NMR of perfluorocycloalkenes and their
products show short range as well as long range coupling, and each
carbon of PFCA ring shows a splitting pattern due to each fluorine
atom present on the ring. For example, in OFCP the b carbon, a,
with two fluorine atoms shows a tquint.t with J = 1375.0, 120.0,
Based on isolated product.
25.4 Hz, and the
a carbon, b, shows a tqm, J = 1287.5, 116.8 Hz
(Fig. S2). As expected, DFCH and its products show a more compli-
cated and unresolved splitting pattern in their 13C NMR spectra
due to the higher number of fluorine atoms (Figs. S4, S15, S18
and S20).
In the case of M1, the 1H NMR spectrum (Fig. S5) shows a dou-
blet of doublet (at 7.41 and 7.67 with J = 8.2 Hz), representing a
symmetric environment. The 19F NMR (Fig. S6) shows well inte-
grated four fluorine peaks, where peak at ꢀ150.45 ppm represents
the terminal vinyl fluorine indicating the addition–elimination
reaction product. The 13C NMR (19F coupled) spectrum (Fig. 4)
shows singlets for the phenylene carbons whereas PFCP ring car-
bon signals undergo short range as well as long range coupling
and therefore a complex pattern is observed. For example, the
allylic carbon, f, shows ttd with J = 1032.1, 98.5, 27.7 Hz whereas
the b carbon, e, shows a broad splitting pattern overlapping with
adjacent carbon, g’s, signals.
Figure 2. ORTEP representation of M1 crystal structure.
CF2
CF2
x
x
F
HO
R'
OH
+
F
O
R
O
NEt3, DMF
80 °C
CF2
CF2
x
x
To further establish the structures and understand the solid-
state nature of these monomers, X-ray analysis was conducted.
Bis-PFCA monomers were purified using column chromatography
with hexanes as the eluent. The purified monomers, M1, M4 and
M6 were obtained as white crystalline solids, while other mono-
mers were highly viscous clear liquids. Attempts to crystallize
M1, M4 and M6 from a multitude of polar and non-polar solvents
were unsuccessful. Finally, recrystallization of M1 and M6 from
chlorobenzene and a mixture of toluene and bromobenzene,
respectively, with a slow evaporation, resulted in the afforded X-
ray quality crystalline solids. Crystal structures for M1 and M6
are shown in Figures 2 and S22, and selected crystal properties
including dihedral bond angles (°) for M1 and M6 are reported in
Tables 2 and S1, respectively.
Figure 2 shows the ORTEP representation for M1. Crystal struc-
ture measurements were carried out at 193 K. The crystal shows
the monoclinic, P21/n space group with no sign of thermal atomic
displacement. Both PFCP rings show a presence of a double bond
(C1–C2 and C18–C19) with a bond length of 1.32 Å. Two phenyl
rings stand with a torsion angle (C8-C9-C12-C13) of 30.8°. The
PFCP ring (with higher numbered carbon) inclined to the phenyl
ring with 90.3°, but the other PFCP ring inclined with 56.6° to
the corresponding phenyl ring. Interestingly, the former PFCP ring
is almost planar, but PFCP ring (with lowered numbered carbon)
shows an envelope conformation with the flap atom, C4.
O
R'
O
O
R
O
n
Scheme 2. General synthesis of PFCA aryl ether polymers from PFCA aryl ether
monomers.
published the first polymerization of PFCAs using a novel step
growth condensation with bisphenols.5 PFCA aryl ether polymers
are highly thermally stable and show variable thermal properties
depending upon the functional spacer group, R (Scheme 2).
Due to the volatility of perfluorocycloalkenes, the stochiometry
ratio is difficult to sustain during polymerization. However, bis-
PFCA aryl ether monomers reported here, not only precludes the
stochiometry ratio issue, but also provides a new synthetic versa-
tility which can afford a variety of random and/or alternating
copolymers with specific design control to be published elsewhere
(Scheme 2).5 These monomers also provide the option of synthesiz-
ing copolymers containing both, OFCP and DFCP moieties.
Attack of the nucleophile on the PFCA double bond generates a
carbanion which can eliminate fluoride resulting in vinyl substi-
tuted and allyl substituted products (Scheme 3). The ratio of vinylic
to allylic products depends on the ring size, reaction conditions
and nucleophile.26 The vinylic product would be the major product
unless the allyl position has a more favored leaving group.26 The
Figure S22 shows the ORTEP representations for molecule A and
molecule B, two conformation structures of M6 crystal. Crystal
data were recorded at 188 K. The crystal shows triclinic, P-1 space
group and a significant amount of thermal displacements, resulting
in the asymmetry in molecules. M6 crystal properties are very dif-
ferent from M1 crystal structural properties because of two extra
trifluoromethyl groups and a bigger PFCA rings. Both molecules A
CF2
CF2
CF2
F
F
x
F
F
Nu-
x
F
x
+
+
F
F
F
F
F
F
F
F
Nu
F
Nu
F
F
x = 1, 2
vinyl substitution
allyl substitution
Scheme 3. General reaction representation for addition–elimination reactions on
perfluorocycloalkenes.
@
and B show the C C bond length of 1.32 Å in PFCH rings as we
@

B. Sharma et al. / Tetrahedron Letters 54 (2013) 3609–3612
3611
Figure 3. 19F NMR of monomer M6. Minor peaks represent the allyl substituted products.
Figure 4. 13C NMR (19F-coupled) of monomer M1. Insets: expanded signals of PFCP ring carbons.
Table 2
ring shows distorted chair to distorted half chair conformation
with atom C14 distorted over two sites (C14 and C14A), and con-
comitant disorder of F atoms on the ring. In molecule B, both PFCH
rings show the half chair conformation; with the high numbered
PFCH ring showing the atomic thermal displacement (F230 and
F23B).
These PFCA monomers (M1–M6) were also characterized with
ATR-FTIR. Figures 5 and S21 show the IR spectrum for monomers
M1–M6. A strong peak at 830 cmꢀ1 represents the typical, out of
plane, aromatic C–H bending mode.39 These spectra show the char-
acteristic bands from 1080 to 1285 cmꢀ1 due to CF2 and C–O–C
asymmetric stretching.35,40 Peaks at 1499 and 1600 cmꢀ1 (strong
and medium intensities respectively) are associated with C@C
stretching for the aromatic rings in these spectra. Figures 5 and
Selected crystal data and structure refinements for monomer M1
Parameters
M1 (°)
C8-C9-C12-C13
C1-O1-C6-C11
C18-O2-C15-C14
C2-C1-C5-C4
30.8
56.6
90.3
10.2
ꢀ1.5
C18-C19-C20-C21
see in M1 crystal. The PFCH rings inclined to the corresponding
phenyl rings with an angle ranging from 62° to 74°. In molecule
A the high numbered PFCH rings shows half chair geometry with
no sign of atomic displacement whereas the low numbered PFCH

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B. Sharma et al. / Tetrahedron Letters 54 (2013) 3609–3612
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products).18 Further, the GC–MS and elemental analyses showed
the expected molecular weight and elemental composition for all
the products M1–M6.
In conclusion, we have developed a new class of PFCA aryl ether
monomers from commercially available feedstocks via an addi-
tion–elimination reaction, in a good isolated yield. These mono-
mers are a substantial step for the synthesis of a wide range of
PFCA homo and copolymers of variable randomness or blockiness.
Acknowledgments
The authors want to express their gratitude to Intel Corporation
(Grant #4606175), Welch Foundation (Grant #AT-0041), NSF-
IUCRC sponsored Center for Energy Harvesting Materials and Sys-
tems (CEHMS) (Grant #IIP-1035024) and the University of Texas
at Dallas for their financial support.
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Supplementary data (crystallographic data for the structures re-
ported in this Letter have been deposited with the Cambridge Crys-
tallographic Data Centre as supplementary publications CCDC
927350 (1) and 927351 (2). Copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax: +44 1233 336 033: e-mail: deposit@ccdc.cam.ac.uk).
A list of detailed experimental procedures, instrumentation and
characterization data (NMR, IR, GC/MS) for all the new compounds)
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.tetlet.2013.04.087.