Suzuki polycondensation and post-polymerization modification toward electro-optic perfluorocyclobutyl (PFCB) aryl ether polymers: Synthesis and characterization

Article abstract of DOI:10.1016/j.jfluchem.2015.10.004

Suzuki polycondensation (SPC) as an alternative strategy has been utilized for the first time to readily yield functional perfluorocyclobutyl (PFCB) aryl ether polymers, which are difficult to obtain via the traditional [2+2] thermal cyclopolymerization s

Full text of DOI:10.1016/j.jfluchem.2015.10.004

Journal of Fluorine Chemistry 180 (2015) 227–233
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Suzuki polycondensation and post-polymerization modification
toward electro-optic perfluorocyclobutyl (PFCB) aryl ether polymers:
Synthesis and characterization
a,
a
a
a
Jingbo Wu *, Benjamin R. Lund , Benjamin Batchelor , Daniel K. Dei ,
b
a
Shawna M. Liff , Dennis W. Smith Jr.
a
Department of Chemistry and the Alan G. MacDiarmid NanoTech Institute, The University of Texas at Dallas, Richardson, TX 75080, United States
Intel Corporation, Chandler, AZ 85226, United States
b
A R T I C L E I N F O
A B S T R A C T
Article history:
Suzuki polycondensation (SPC) as an alternative strategy has been utilized for the first time to readily
yield functional perfluorocyclobutyl (PFCB) aryl ether polymers, which are difficult to obtain via the
traditional [2+2] thermal cyclopolymerization strategy. Using two reactive PFCB aryl ether molecules as
monomers, the biphenyl PFCB aryl ether polymer without any functionality was first prepared and
Received 22 July 2015
Received in revised form 22 September 2015
Accepted 4 October 2015
Available online 22 October 2015
2
exhibited good thermal stability, up to 450 8C at 8% weight loss (N ). By choosing appropriate functional
monomers, aldehyde-functionalized PFCB aryl ether polymer precursor was also successfully prepared.
Post-polymerization modification of this polymer precursor via Knoevenagel condensation yielded three
distinct PFCB aryl ether polymers containing thermally stable triarylamine-based electro-optic
chromophores.
Keywords:
Suzuki polycondensation
Post-polymerization modification
Electro-optics
ß 2015 Elsevier B.V. All rights reserved.
Knoevenagel condensation
Perfluorocyclobutane
Functional semi-fluorinated polymers
1
. Introduction
Perfluorocyclobutyl (PFCB) aryl ether polymers are a unique
TFVE molecules (e.g. p-trifluorovinyl bromobenzene or p-trifluor-
ovinyl benzoic acid, Scheme 1, Route 1). This attractive technology
has some limitations. When complex functional structures are
required, sometimes it is difficult or impossible to synthesize the
corresponding functional TFVE monomers. Direct polymerization
of functional TFVE monomers via the [2+2] thermal cyclodimer-
ization cannot always yield desired functional PFCB aryl ether
polymers because some functional groups cannot tolerate the high
polymerization temperature or may undergo side reactions with
TFVE groups during the polymerization process. It has been
observed that hydrocarbon olefins (e.g. the double bonds in
conjugated NLO chromophores) and aldehyde groups can undergo
thermal [2+2] cycloaddition reaction with TFVE groups [12,13].
Alternatively, functional PFCB aryl ether polymers can be
prepared via the standard step-growth polymerization of reactive
PFCB aryl ether monomers with functional monomers (Scheme 1,
Route 2). Reactive PFCB aryl ether monomers are usually prepared
from their corresponding mono-functional TFVE molecules via the
thermal [2+2] cyclodimerization (Scheme 1, Route 2) [12,14–18].
The synthetic Route 2 has some obvious advantages: functional
monomers are much easier to synthesize compared to their
corresponding functional TFVE monomers and polymerizations
can be performed at much lower temperatures. Up to now,
Wittig condensation polymerization [12], the Huisgen’s 1,3-dipolar
class of amorphous semi-fluorinated polymers, which exhibit a
combination of high performance properties such as excellent
thermal stability, oxidative stability, chemical resistance, low
surface energy, low optical loss, and high electrical insulating
ability [1]. As a result, PFCB aryl ether polymers have been utilized
in many areas, such as proton exchange membranes (PEMs) in
hydrogen–oxygen fuel cells [2], organic nonlinear optic (NLO) host
polymers [3–6], organic nanomaterials [7], photonics [8], fire
retardant materials, and polymer light emitting diodes [9,10].
Introduction of functionalities into PFCB aryl ether polymers is
used to tailor their applications. Functional PFCB aryl ether
polymers are traditionally prepared via a [2+2] thermal cyclodi-
merization of appropriate functional aromatic trifluorovinylether
(TFVE) monomers above 150 8C in bulk or in a solution without any
catalyst (Scheme 1, Route 1) [11]. Functional TFVE monomers
usually are prepared via reactions of their corresponding
functional monomer precursors with the mono-functional reactive
*
Corresponding author.
E-mail address: wjbsioc2013@gmail.com (J. Wu).
http://dx.doi.org/10.1016/j.jfluchem.2015.10.004
022-1139/ß 2015 Elsevier B.V. All rights reserved.
0

2
28
J. Wu et al. / Journal of Fluorine Chemistry 180 (2015) 227–233
literatures due to the difficulty in the synthesis of the correspond-
ing functional monomers. In this article, the biphenyl PFCB aryl
ether polymer without any functionality was first synthesized via
Suzuki polycondensation (SPC in Scheme 2). The properties of the
resulting polymer PSPC were compared to those of a commercially
available polymer PTCP used as a reference. Then PFCB aryl ether
polymers containing triarylamine-based chromophores were
synthesized via Suzuki polycondensation and post-polymerization
modification procedures (Scheme 3). Our results show Suzuki
polycondensation is suitable to prepare functional PFCB aryl ether
polymers, which allows us to develop many new functional PFCB
aryl ether polymers to further broaden their applications.
2. Results and discussion
2.1. Synthesis and characterization of monomers and polymers
Reactive PFCB aryl ethers M1 and M2 were prepared from
commercially available mono-functional TFVE molecules via the
thermal [2+2] cyclodimerization in good yields (Scheme S1) [22],
1
19
whose structures were confirmed by H NMR and F NMR spectra.
Suzuki polycondensation of these two monomers afforded a
biphenyl PFCB aryl ether polymer PSPC in a good yield (71%), which
is analogous to the commercially available biphenyl PFCB aryl
ether polymer PTCP prepared via the thermal [2+2] cyclodimeriza-
tion polymerization process. The number-average molecular
weight (M
400 g/mol with a polydispersity index (PDI) of 1.7 by size
exclusion chromatography (monodisperse polystyrene standards,
n
) for purified polymer PSPC was determined to be
5
19
THF as the eluent). The structure of polymer PSPC was probed by
F
NMR spectroscopy, which displayed characteristic PFCB spectro-
scopic patterns as seen in PTCP (Fig. 1). The ATR-FTIR spectrum of
Scheme 1. Two synthetic routes to synthesize functional PFCB aryl ether polymers.
PSPC shows a broad, strong absorbance of the PFCB ring breathing
À1
19
mode appeared at 960 cm (Fig. S1). Both F NMR and ATR-FTIR
results indicated that the PFCB ring in the monomers did not
participate in significant side reactions during Suzuki polyconden-
sation process. Polymer PSPC has different end groups with
polymer PTCP (Scheme 2). The end groups of polymer PTCP are
cycloaddition polymerization [19], nucleophilic aromatic substitu-
tion polymerization [18], and palladium catalyzed amination
polymerization [15] have been successfully performed to prepare
functional PFCB aryl ether polymers via the synthetic Route 2. To our
best knowledge, Suzuki polycondensation has not been utilized to
prepare functional PFCB aryl ether polymers.
Some electro-optic (EO) chromophore-functionalized PFCB aryl
ether thermosetting polymers had been prepared via [2+2]
thermal cyclodimerization of their corresponding TFVE monomers
1
9
aryl TFVE groups shown in its F NMR spectrum (the characteristic
pattern at ꢀÀ119, À126, and À134; Fig. 1). Polymer PSPC has two
different end groups: the bromine end group and the boronate
1
ester end group (Scheme 2). The H NMR spectrum of polymer PSPC
shows a small signal at 1.26 ppm, which is associated to the
hydrogen atoms of boronic perco-ester end groups (Fig. S2). The
results from thermogravimetric analyzer/mass spectrometer
(TGA–MS) studies show that polymer PSPC also contains some
bromine end groups (Fig. S6). Due to containing two different end
(
[
Scheme 1, Route 1) and showed very good EO properties
20,21]. However, no PFCB aryl ether polymer containing thermally
stable triarylamine-based EO chromophores is reported in the
Scheme 2. Two synthetic routes to biphenyl PFCB aryl ether polymers: Suzuki polycondensation (SCP) and thermal [2+2] cyclodimerization polymerization (TCP). End groups
X) vary as a function of the polymerization route.
(

J. Wu et al. / Journal of Fluorine Chemistry 180 (2015) 227–233
229
Scheme 3. The synthetic route to PP via Suzuki polycondensation and P1–P3 via post-polymerization modification.
groups, the molecular weight of polymer
determined from end-group analysis by NMR.
P
SPC cannot be
The final triarylamine-based EO chromophore-functionalized
polymers P1–P3 were prepared using post-polymerization modi-
fication via Knoevenagel condensation reactions of the aldehyde-
functionalized polymer precursor PP with three different electron
acceptors: 1,3-diethyl-2-thiobarbituric acid (BBA), 2-(3-cyano-
4,5,5-trimethyl-5H-furan-2-ylidene)malononitrile (TCF), and mal-
ononitrile (MA), respectively (Scheme 3). The signal of the
aldehydic proton in polymer PP at 9.91 ppm is absent in the
spectra of the final functional polymers P1–P3, meanwhile, signals
of olefinic protons connecting with electron acceptors appear at
8.64 ppm for P1 and 8.09 ppm for P2, confirming the formation of
the full conjugated EO chromophores on the side chains (Fig. S3).
For P3, the signals of olefinic protons are obscured by the signals of
backbone aromatic protons and are hard to identify (Fig. S3). The
To obtain electro-optic (EO) chromophore-functionalized PFCB
aryl ether polymers, the EO chromophore precursor-functionalized
monomer M3 (Scheme 3) was synthesized by following previously
published procedures (Scheme S1) [23] and its structure was
1
13
confirmed by H NMR (Fig. S8) and
C NMR spectroscopy.
Copolymerization of monomers M1–M3 afforded an aldehyde-
appended PFCB aryl ether polymer precursor PP in a good yield
(
Scheme 3). In this polymerization reaction, feed molar ratios of
M1, M2 and M3 (40:50:10) were controlled in order to obtain a
polymer with a desired chromophore loading (around 10%). The
actual chromophore loading of the resulting polymer PP was
1
determined from its H NMR spectrum. Integration ratio between
the aldehyde proton and biphenyl protons is 1:10.
integration ratio of the double bond proton, which was close to the
1
electron acceptor group BBA, and biphenyl protons from the
H
NMR spectrum of P1 is determined to be 1:10 (Fig. S4). The
percentage of chromophore in final polymer P1 did not change
compared to that of the polymer precursor PP, indicating the
polymer matrix is inert and compatible with this mild post-
polymerization modification condition.
The physical properties of the commercially available PFCB aryl
ether polymer PTCP used as a reference and the resulting PFCB aryl
ether polymers PSPC, PP, and P1–P3 are summarized in Table 1. As
shown in Table 1, the molecular weights of the resulting polymers
PSPC, PP, and P1–P3 were relatively low and oligomeric in nature.
The increased number-average molecular weights (M ) and
n
decreased PDIs of P1–P3 compared to PP are attributed to the
purification employed after post-polymerization modification,
which removed fragments with lower molecular weights. The
resulting polymers PSPC, PP, and P1–P3 exhibit excellent solubility
in various organic solvents such as chlorobenzene, acetone,
chloroform and THF.
2.2. Thermal properties
19
Fig. 1. F NMR spectra for PTCP (top) and PSPC (bottom). TFVE end groups, present in
TCP, are absent in PSPC, however, PFCB structure (À128 to À131 ppm) is present in
both TCP and confirming the similar product from the two separate
polymerization routes.
The thermal properties of polymer PSPC were investigated via
DSC and compared to polymer PTCP (Fig. S5). Whereas polymer
TCP had a glass transition at 130 8C, polymer PSPC has a
P
P
SPC
P ,
P

2
30
J. Wu et al. / Journal of Fluorine Chemistry 180 (2015) 227–233
Table 1
Molecular weights and thermal properties of the PFCB aryl ether polymers.
onset
d
a
b
c
d
e
Entry
M
n
(g/mol)
M
w
(g/mol)
PDI
T
(8C)
T
g
(8C)
E1/2 (eV)
E
ox (eV)
l
onset (nm)
E
gap (eV)
E
HOMO (eV)
ELUMO (eV)
P
P
TCP
24,000
5400
3600
5700
5500
4500
44,000
9200
8500
7100
6900
6000
1.8
1.7
2.4
1.3
1.3
1.3
450
245
220
230
206
200
130
109
93
–
–
–
–
–
–
–
SPC
f
–
–
–
–
–
PP
0.48
0.47
0.43
0.47
0.36
0.33
0.33
0.27
500
668
754
613
2.48
1.86
1.64
2.02
5.16
5.13
5.13
5.07
2.68
3.37
3.49
3.05
f
P1
P2
P3
130
128
110
f
f
a
E
ox taken from the straight line approximation of the onset of oxidation in the CV voltammogram.
onset taken from the straight line approximation of the onset of absorption in the UV–vis spectrum.
onset, Egap = 1240 nm Á V/
b
c
d
e
f
l
E
gap estimated from
l
onset
l .
E
HOMO = Eox + 4.8.
E
LUMO = EHOMO À Egap
.
1
0 wt% chromophore.
significantly lower glass transition at 109 8C due to a much lower
number-average molecular weight of the polymer chains of PSPC
compared to PTCP, 5400 and 24,000, respectively (Table 1). The
aldehyde-functionalized polymer precursor PP exhibits the lowest
glass transition temperature (around 93 8C). The three full EO
chromophore-functionalized PFCB aryl ether polymers P1–P3,
P1–P3 have similar degradation patterns (two step degradation)
with the polymer PSPC and a slightly larger weight loss (ꢀ15%)
during the first step degradation. The reduced thermal stability of
the functional polymers P1–P3 compared to the polymer PSPC is
due to the degradation of the side-chain EO chromophores (the
chromophores begin to degrade at 250 8C) [13,25,26], and some
impurities (unreacted acceptors) in the samples.
g
have relatively higher T s.
The thermal stability and degradation byproducts of polymer
P
SPC and polymer PTCP were probed by TGA (Fig. 2) and TGA–MS
2.3. Optical and electrochemical properties
(
Fig. S6) techniques. The TGA thermogram of polymer PSPC shows a
two-step degradation process (Fig. 2). The first step degradation
process mainly takes place at around 250 8C, the second step
degradation takes place at around 450 8C. For the first step
degradation, TGA–MS results show a loss of bromobenzene
The absorption spectra of the resulting polymers PP and P1–P3
were measured in dilute chloroform (1 g/L) (Fig. 3). The polymer
solutions are shown in Fig. 3, and reveal significant contrasts in
color: yellow (PP), purple (P1), blue (P2) and orange (P3). All these
four polymers exhibit three or four major absorption bands in the
UV–vis spectra. The first strongest absorption peak at ꢀ260 nm is
followed by a weaker absorption ꢀ350 nm, these peaks correspond
(156 amu and 158 amu) and a loss of benzene ring (78 amu),
which suggests the major weight loss (around 8% weight loss) of
polymer PSPC from 220 8C to 300 8C comes from the degradation of
a large amount of the bromobenzene end group due to its low
molecular weight. For the second step degradation, TGA–MS
results show polymer PSPC has the same mass fragmentation
pattern as polymer PTCP at the temperatures of 450 8C and on.
These mass fragments of the second step degradation showed a
good agreement with previously reported literature values of
degradation of common PFCB aryl ether polymers [24]. The main
mass fragments are listed at 93 amu which corresponds to a
phenol, then at 162 amu corresponding to a hexafluorocyclobu-
tane ring. Over all, the polymer PTCP has good thermal stability up
to 450 8C with 8% weight loss (bromobenzene end groups) in an
inert atmosphere.
to the
p–p* transition of biphenyl and conjugated chromophore
side chains, respectively. Further absorbance is correlated to the
intramolecular charge transfer (ICT) from the triphenyl amino
groups (n–p*) in the main chain to the acceptor groups or aldehyde
group in the pendent side chains. The lowest energy ICT absorption
peaks of PP (aldehyde), P1 (BBA), P2 (TCF), and P3 (MA) are
430 nm, 570 nm, 619 nm, and 517 nm, respectively. This trend
matches the strength of the electron acceptor groups. The stronger
electron acceptors produce the larger the absorption peaks in the
absorption spectra.
The electronic structures of the resulting polymers PP and
P1–P3 were studied by cyclic voltammetry and UV–vis techniques
to explore their potential applications in photonic systems. While
the half wave potentials (E1/2) for these four polymers were fairly
similar, Æ0.03 V, their redox couple resided ꢀ0.2 V more anodic than
analogous single molecule chromophores (Table 1 and Fig. S7)
The polymer precursor PP has a huge weight loss (ꢀ30%) from
2
00 8C to around 450 8C (Fig. 2) and exhibits much less thermal
stability compared to the polymer PSPC due to the degradation of
the aldehyde pending chromophore precursors on the side chains
[
13,25,26]. The final EO chromophore-functionalized polymers
100
PTCP
PSPC
90
80
70
60
50
40
P1
P3
P2
PP
100
200
300
4o00
500
600
Temperature ( C)
Fig. 3. UV–vis absorption spectra and picture of polymer (PP and P1–P3) solutions
Fig. 2. Thermograms of PFCB aryl ether polymers PSPC, PTCP, PP, and P1–P3.
in chloroform.

J. Wu et al. / Journal of Fluorine Chemistry 180 (2015) 227–233
231
[
13]. The increase in the oxidation potential suggests a decrease in the
commercial BP-PFCB polymer (hereafter PTCP) purchased from
Tetramer Technologies, LLC was used as a reference material. All
other reagents were purchased from Aldrich or Alfa Aesar and used
without further purification.
electronic density of the donor functionality due to the substitution
and conformation effects on triarylamine-based electron donors (RO-
3
phenyl- vs. –OCH ) [27].
The band gaps of the full EO chromophore-functionalized
polymers were measured by UV–vis spectroscopy by taking the
onset of absorption of lowest energy transition in each polymer
and converting it to electron volts. Good correlation was found
between the strength of the acceptor groups and the extent of the
bathochromic shifts (from PP), with stronger groups producing
larger shifts in Egap (from 1.64 to 2.48 V).
Additionally, the highest occupied molecular orbital (HOMO)
energies and lowest unoccupied molecular orbital (LUMO)
energies were obtained utilizing the onset of oxidation in the
CV as an anchor point (Table 1), correcting to vacuum and
subtracting the approximated band gap. While a little change in
the HOMO was observed across the series (0.09 V), substantial
variation in the LUMO (0.81 V) was seen as a function of the
strength of electron acceptor groups.
4.2. Analysis
1
13
19
H, C and F NMR spectra were recorded on a Bruker 400 or
500 MHz NMR and chemical shifts were measured in ppm ( ) with
d
reference to an internal standard: tetramethylsilane (0 ppm),
deuterated chloroform (77 ppm), and trichlorofluoromethane
(0 ppm) for H, C and F NMR, respectively. ATR-FTIR was
recorded on a Shimadzu IR-Affinity 1 in ATR module with a
germanium probe. Experiments were tested in transmissionmode at
a resolution of 4.0 measuring between 700 cm and 4000 cm for
32–72 scans. Ultraviolet–visible absorption spectra were measured
using an Agilent 8453 UV–vis spectroscopy system. Differential
scanning calorimetry (DSC) analysis was performed on a Mettler
Toledo DSC 1 system under nitrogen at a heating rate of 10 8C/min.
1
13
19
À1
À1
g
The glass transition temperature (T ) was obtained from a second
3
. Conclusion
heating cycle using Star E version 10.0 software suite. Thermal
gravimetric analysis (TGA) was performed on a Mettler-Toledo TGA/
DSC 1 LF instrument under nitrogen at a heating rate of 10 8C/min up
to 800 8C. Thermogravimetric analysis with mass spectroscopy
(TGA–MS) was performed on a Mettler TGA/DSC-1 and a Pfeiffer
PrismaPlus QMG-220 as the mass spectrometer. The TGA method
was set with a rate of 5 8C/min from 30 8C to 800 8C while scanning
themassspectrometerfrom30 amu to200 amusimultaneously. The
results were then imported into Origin for data analysis. Gel
permeationchromatography(GPC)datawerecollectedinTHFfroma
Waters 2690 Alliance System with photodiode array detector. GPC
samples were eluted in series through Polymer Labs PLGel 5 mm
Mixed-D and Mixed-E columns at 35 8C. Molecular weights
were obtained using polystyrene as a standard (Polymer Labs
Easical PS-2). Electrochemical measurements were performed in a
0.1 M solution of electrochemical grade tetrabutylammonium
Suzuki polycondensation for the first time has been successfully
utilized to prepare a PFCB aryl ether polymer PSPC without any
functionality and an aldehyde-functionalized PFCB aryl ether
polymer precursor PP, which is difficult to synthesize via [2+2]
thermal cyclodimerization due to the reaction of the aldehyde
groups with TFVE groups at high temperatures. The polymeriza-
tions were performed at a much lower temperature (80 8C) than
the required high polymerization temperatures (>150 8C) for
traditional synthetic route via [2+2] thermal cyclodimerization,
which allows us to prepare more functional PFCB aryl ether
polymers. The physical properties of PSPC have been compared to
the literature and commercial standard. The polymer
P
SPC
maintains good thermal stability of PFCB aryl ether polymer.
The decrease in thermal stability is mainly due to the less
thermally stable bromobenzene end groups presenting in polymer
6
hexafluorophosphate (TBAPF ) in dichloromethane. All samples
P
SPC. Further, the full triarylamine-based chromophore-function-
were gently purged with nitrogen prior to scanning and run under an
inert atmosphere (note: purging must be gentle to avoid solvent
evaporation and change in electrolyte concentration). Cyclic
voltammetry was carried out on a BASi CV-50W analyzer with a
platinum working electrode, platinum wire auxiliary electrode, and
alized PFCB aryl ether polymers P1–P3 were successfully prepared
by post-polymerization modification via Knoevenagel condensa-
tion of PP with different electron acceptors. The advantage of this
method is that three EO polymers are obtained from just one
polymer precursor. These three polymers exhibit high solubility and
good thermal stability. Future works will focus on improving the
molecular weight of the PFCB aryl ether polymers prepared via
Suzuki polycondensation, increasing their thermal stability by
removing the potentially reactive bromo and boronic ester
functionalities through end capping, incorporating more functional
groups into PFCB aryl ether polymers to extend their applications.
+
Ag/AgCl reference electrode. Samples were calibrated to the Fc/Fc
couple.
4.3. Synthesis of PSPC
1,2-Bis{4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan2-yl)pheno-
xyl}hexafluorocyclobutane (M2) (348 mg, 0.6 mmol) and 1,2-
bis(4-bromophenoxyl)hexafluorocyclobutane (M1) (291 mg,
0.6 mmol) were placed into a 50 mL two-neck round-bottom
4
. Experimental
.1. Materials
-(1,2,2-Trifluorovinyloxy) phenylboronic acid and 4-(4,4,5,5-
2 3
flask. A mixture of 2 M K CO aqueous solution (2 mL) and THF
4
(20 mL) were added into the flask and the reaction mixture were
degassed followed by the addition of a catalytic amount of
4
Pd(PPh
3
)
4
(66 mg, 0.06 mmol). The reaction mixture was then
atmosphere.
tetramethyl-1,3,2-dioxaborolan2-yl)-phenyl trifluorovinyl ether
were donated by and are commercially available from Tetramer
Technologies, LLC and distributed though Oakwood Chemicals, Inc.
refluxed with vigorous stirring for 72 h under an N
2
The reaction mixture was cooled to room temperature, and then
was poured into methanol (100 mL) and the resulting light yellow
precipitate was collected through vacuum filtration and washed
sequentially with D.I. water, MeOH, and hexanes. The solid
polymer was then dried in a vacuum oven at 60 8C for an additional
2
-(2-{4-[N,N-Di(4-bromophenyl)amino]phenyl}ethenyl)thien-5-al
(M3) (Scheme S1) [23] and 2-(3-cyano-4,5,5-trimethyl-2(5H)-
furanylidene)-propanedinitrile (TCF) were synthesized according
to published procedure [28]. 1,2-Bis(4-bromophenoxyl)hexafluor-
ocyclobutane (M1) and 1,2-bis{4-(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan2-yl)phenoxyl}henxafluorocyclobutane (M2) were prepared
from their corresponding TFVE monomers according to previously
published procedures (Scheme S1) [22]. For comparative purposes,
24 h to afford PSPC as a light yellow powder (285 mg, 71%).
1
3
H NMR (500 MHz, CDCl ) d 7.49 (s, 4H), 7.23 (dd, J = 28.8,
19
6.9 Hz, 4H), 1.31 (d, J = 31.1 Hz, 2H), 0.99–0.78 (m, 1H). F NMR
(471 MHz, acetone-d
À127.5 (s), À129.5 (s), À120.0 (s), À130.6
(s), À130.8 to À131.5 (m), À131.3 (s), À131.5 (s), À131.8 (s).
6
) d

2
32
J. Wu et al. / Journal of Fluorine Chemistry 180 (2015) 227–233
4.4. Synthesis of PP
J = 4 Hz), 7.43 (d, J = 4 Hz) 7.26 (d, J = 4 Hz), 7.20 (d, J = 4 Hz), 7.15
1
3
(
s), 7.10 (d, J = 4 Hz), 7.08–7.05 (m); C NMR (101 MHz, CDCl
3
) d
To a 25 mL two-neck round-bottom flask containing 1,2-bis (4-
161.1, 152.1, 152.0, 137.2, 136.9, 134.5, 134.1, 132.8, 130.8, 128.3,
1
9
bromo-phenoxyl)
.6 mmol), 1,2-bis (4-boro-perco-ester-phenoxyl) hexafluorocy-
clobutane (M2) (600 mg, 1 mmol), and 2-(2-{4-[N,N-di-(4-bromo-
phenyl) amino]phenyl}ethenyl)thien-5-al (M3) (210 mg,
.4 mmol) was added 13 mL of a base/solvent mixture (3:10,
M K CO (aq):THF), after which the reaction mixture was
hexafluorocyclobutane
(M1)
(307 mg,
128.2, 128.0, 119.0, 118.8, 118.5, 116.2, 115.6; F NMR (376 MHz,
CDCl
0
3
)
d
À125.1, À127.4, À127.5, À128.0, À128.1, À128.3, À128.8,
À128.9, À129.0, À129.5, À129.6, À129.7, À130.2, À130.4, À130.7;
À1
ATR-FTIR (cm
) n 2219, 1604, 1493, 1435, 1396, 1303, 1264, 1194,
0
2
1167, 1116, 1007, 956, 899, 822.
2
3
degassed followed by the addition of a catalytic amount of
Pd(PPh (21 mg, 0.018 mmol). The reaction mixture was then
refluxed with vigorous stirring for 72 h under an N atmosphere.
The reaction mixture was then cooled and poured into MeOH
100 mL), after which the resulting yellow precipitate was
collected through filtration and washed sequentially with D.I.
O and hexanes. The solid polymer was then dried in a vacuum
oven at 60 8C for an additional 24 h to afford PP as a yellow powder
Acknowledgements
3 4
)
2
The authors wish to thank Intel Corporation for their guidance
and support. The authors would also like to thank the Welch
Foundation (Grant AT-0041), the Alan G. MacDiarmid NanoTech
Institute, the National Science Foundation through the Center for
Energy Harvesting Materials and Systems (NSF-I/UCRC, grant
(
H
2
1035024) and the University of Texas at Dallas for their support.
1
(
800 mg, 80%). H NMR (400 MHz, CDCl
3
)
d
9.91 (s, CHO), 7.89 (s),
.82–7.02 (m), 6.97 (s); C NMR (101 MHz, acetone-d 152.1,
51.8, 137.3, 137.0, 134.7, 133.2, 133.1, 129.9, 128.6, 128.5, 127.9,
13
7
1
1
6
)
d
Appendix A. Supplementary data
19
19.0, 118.6; F NMR (376 MHz, CDCl
3
)
d
À126.1, À127.3, À127.5,
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.jfluchem.2015.
10.004.
À128.0, À128.1, À128.9, À129.5, À129.6, À130.2, À130.4, À130.7,
À1
À130.9, À131.1; ATR-FTIR (cm
) n 1669, 1602, 1493, 1301, 1264,
1
196, 1170, 1115, 1006, 958, 822.
.5. Synthesis of P1
Triethylamine (0.1 mL, 0.7 mmol) was added in excess to a
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