Conjugated poly(fluoroalkyl 3-thienylacetate)s synthesized in supercritical carbon dioxide

Full text of DOI:10.1134/S0012500812040039

ISSN 0012ꢀ5008, Doklady Chemistry, 2012, Vol. 443, Part 2, pp. 101–106. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © M.L. Keshtov, A.M. Lopatin, D.V. Marochkin, FangꢀChung Chen, A.R. Khokhlov, 2012, published in Doklady Akademii Nauk, 2012, Vol. 443, No. 5,
pp.586–591.
CHEMISTRY
Conjugated Poly(fluoroalkyl 3ꢀthienylacetate)s
Synthesized in Supercritical Carbon Dioxide
M. L. Keshtova, A. M. Lopatina, D. V. Marochkina, FangꢀChung Chenb,
and Academician A. R. Khokhlova
Received December 29, 2011
DOI: 10.1134/S0012500812040039
Conjugated polymers and supercritical carbon attract enhanced attention due to a unique combinaꢀ
dioxide (scꢀCО2) in recent time have attracted a conꢀ tion of electronic properties such as electrochemical
stability, photoꢀ and electrical conductivity, electroꢀ
chromism, facile structural modification, etc. Howꢀ
ever, these polymers are insoluble in scꢀCО2. A numꢀ
siderable attention of researchers not only from scienꢀ
tific but also from practical viewpoint on account of
their use in different areas of science and technology.
These polymers are intensely used as electroactive ber of authors showed that poly(fluoroalkylthioꢀ
materials for lightꢀemitting diodes, fieldꢀeffect tranꢀ phene)s, on the contrary, are soluble in scꢀCО2 [12, 13].
sistors, electrochromic devices, chemosensors, and
Taking into account the fluorophilicity of scꢀCО2
solar photoelectric cells [1–7], whereas scꢀCО2
[10] and strong interaction between scꢀCО2 and carboꢀ
behaves as an environmentallyꢀfriendly “green” solvent
nyl groups [14], we have modified the polythiophene
that becomes a real alternative to organic solvents for
chain with fluoroalkyl ester groups to obtain polymers
different chemical processes, including fine organic
synthesis and polymer preparation [8, 9]. However, the
practical application of scꢀCО2 for the synthesis of
polymers is confined on account of poor solubility of
the majority of polymers except for amorphous fluoꢀ
rineꢀcontaining polymers and silicones [10].
well soluble in scꢀCО2. In this work, we obtained a series
of novel conjugated polythiophenes containing fluoroꢀ
alkyl ester groups in the side chain using scꢀCО2 as a
solvent.
At present, fluoropolymers are widely studied due
to their low surface energy, chemical and thermal staꢀ
bility, hydrophobicity, and the ability of fluoroalkyl
RESULTS AND DISCUSSION
To obtain novel conjugated poly(fluoroalkyl 3ꢀ
chain to selfꢀorganization [11]. The combination of thienylacetate)s, we developed monomers, fluoroalkyl
unique characteristics of fluorine and electronic charꢀ 3ꢀthienylacetates
. The synthesis of compounds
acteristics of conjugated polymers can lead to the
was carried out according to scheme that implies
1–5
1–5
development of novel materials that are of great interꢀ the conversion of 3ꢀthienylacetic acid into correꢀ
est from the viewpoint of both basic and applied sponding acid chloride followed by its reaction with
research. Among numerous conjugated polymers fluoroalkyl alcohols to form fluoroalkyl 3ꢀthienylaceꢀ
under study, polythiophenes and their derivatives tates
1–5.
O
O
O
OH
Cl
O R
4
3
2
SOCl2
HO–R
Py
S
1
S
S
1–5
[R = CH2(CF2)4CF3 (1); CH2(CF2)5CF3 (2); (CH2)3(CF2)5CF3 (3);
CH2(CF2)7CF3 (4); (CH2)2(CF2)7CF3 (5)].
Scheme 1.
a Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, ul. Vavilova 28,
Moscow, 119991 Russia
b National Chiao Tung University, 1001 University Road,
Hsinchu, Taiwan
The composition and structure of target comꢀ
pounds were confirmed by elemental analysis
data, IR spectroscopy, and 1H and 19F NMR (Table 1).
1–5
101

102
KESHTOV et al.
Table 1. Spectral characteristics of thiophene monomers 1–5
Elemental analysis,
found/calculated, %
Monoꢀ
mer
Tm
,
°
C
1H NMR,
δ
, ppm
19F NMR,
, ppm
δ
С
H
F
S
1
115 a 7.34 (dd,
2.0, 1.0 Hz, 1H), 7.09 (dd,
1H), 4.67 (t, 13.7 Hz, 2H), 3.80 (s, 2H) –81.39 (CF3)
J
5.0, 3.0 Hz, 1H), 7.22 (dd,
–126.65 (2F), –123.86 (2F),
34.00 1.61 49.00 7.66
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀ
J
J
5.0, 1.2 Hz, –123.28 (2F), –119.89 (2F),
33.97 1.66 49.26 7.56
J
2
3
120 a 7.30 (dd,
4.9, 3.0 Hz, 1H), 7.19 (m, –126.67(2F), –123.75 (2F),
J
1H), 7.06 (dd, 4.9, 1.1 Hz, 1H), 4.63 (t, –123.26 (2F), –122.53 (2F),
33.16 1.32 52.03 7.15
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀ
J
13.6 Hz, 2H), 3.77 (s, 2H)
32.92 1.49 32.08 6.76
J
–119.94 (2F), – 81.50 (CF3)
38
7.30 (dd,
J
5.0, 3.0 Hz, 1H), 7.17 (dd,
J
1.9, –126.63 (2F), –123.86 (2F),
35.91 2.22 49.27 6.43
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀ
0.8 Hz, 1H), 7.07 (dd,
4.20 (t, 6.3 Hz, 2H), 3.69 (s, 2H), 2.21– –114.86 (2F), –81.49 (CF3)
2.09 (m, 2H), 1.97 (dt, 16.6, 6.2 Hz, 2H)
J 5.0, 1.1 Hz, 1H), –123.28 (2F), –122.28 (2F),
35.87 2.21 49.17 6.38
J
J
4
5
45
40
7.33 (dd,
1H), 7.07 (dd, 5.0, 1.0 Hz, 1H), 4.64 (t, –122.93 (2F), –122.13 (6F),
J
5.0, 3.0 Hz, 1H), 7.21 (m,
–126.40 (2F), –123.49 (2F),
31.30 1.07 56.30 5.67
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀ
J
13.6 Hz, 2H), 3.79 (s, 2H)
31.37 1.22 56.25 5.58
J
–119.71(2F), –81.11 (CF3)
7.32 (dd,
7.07 (dd,
2H), 3.71 (s, 2H), 2.56–2.44 (m, 1H)
J 4.9, 3.0 Hz, 1H), 7.19 (m, 1H), –126.64 (2F), –123.91 (2F),
33.57 1.53 53.96 6.07
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀ
J
5.0, 1.1 Hz, 1H), 4.44 (t, J6.6 Hz, –123.14 (2F), –122.30 (6F),
32.55 1.54 54.90 5.45
–122.04 (2F), –81.39 (CF3)
a
Bp at 2 mmHg.
In particular, the IR spectra of all monomers
1–5
form in the presence of FeCl3 as a catalyst. The polyꢀ
show a strong absorption band typical of carbonyl
mers were prepared in chloroform at ambient temperꢀ
1
group in the region 1738–1762 cm–1. The H NMR ature, while polymerization in scꢀCО2 was conducted
spectra of compounds
1–5
in the region
δ
= 7.40–
at 35–40°С to achieve supercritical state. The oxidaꢀ
7.00 ppm show two doublets of doublets and one douꢀ
blet arising from the different protons of the thiophene
fragment (Table 1). In the aliphatic region, the specꢀ
tive polymerization of fluoroalkyl 3ꢀthienylacetates in
both solvents proceeded successfully with rather high
yields: 80–91 and 70–79%. However, the conversion
in scꢀCО2 was slightly lower, probably because of poor
trum shows a singlet at = 3.7 ppm related to the proꢀ
δ
tons of the methylene group directly bound to the
thiophene ring. Moreover, the integrated intensity
ratio of the aliphatic to aromatic fragments agrees well
with the suggested structures. The 19F NMR spectra of
solubility of FeCl3 in scꢀCО2. All polymers I–V are
soluble in common and fluorinated organic solvents.
Nonetheless, partially soluble polymers were obtained
on prolonged polymerization (longer than 2 h). The
different solubility may be associated with crosslinking
of PFT at the 4ꢀposition of the thiophene ring.
compounds
nals typical of СF3 group. The number of signals in the
19F NMR spectra of all monomers
corresponds to
1–5
in the region of
δ
= 80 ppm show sigꢀ
1–5
The structure of the polymers was confirmed by the
IR and 1H and 19F NMR spectra (Fig. 1, Table 2). In
particular, the IR spectra of all polymers I–V exhibit
the number of fluorine atoms in the molecules of these
compounds.
The synthesis of poly(fluoroalkyl 3ꢀthienylaceꢀ
tate)s (PFT) I–V was accomplished under conditions
of the Sugimoto reaction [15] according to the
scheme:
bands typical of carbonyl group in the region 1737–
1762 cm–1. The 1H NMR spectra of the polymers disꢀ
play signals in the range 6.91–7.65 ppm arising from
the aromatic protons of the thiophene ring. The sigꢀ
nals in the range 4.42–2.50 ppm refer to aliphatic proꢀ
tons. The ratio of integrated intensity of the signals of
the aliphatic to aromatic portions agrees well with the
suggested structures for all polymers. Poly(fluoroalkyl
3ꢀthienylacetate)s obtained in scꢀCО2 and chloroform
have similar structures.
O
O
O R
O R
FeCl3
CKꢀCO2
*
*
n
S
S
1–5
I–V
Scheme 2.
1
Poly(fluoroalkyl 3ꢀthienylacetate)s were obtained
We also used H NMR spectra to study the PFT
by the oxidative polymerization of fluoroalkyl 3ꢀthieꢀ microstructure. Indeed, the signal at
δ
= 3.7 ppm from
nylacetates in supercritical carbon dioxide and chloroꢀ the methylene group directly bound to the thiophene
DOKLADY CHEMISTRY Vol. 443
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2012

CONJUGATED POLY(FLUOROALKYL 3ꢀTHIENYLACETATE)S
103
(a)
O
b
c
a
O
CH (CF ) CF
2
2 4
3
c
n
S
b
a
7.6
7.2
6.8
6.4
6.0
5.6
5.2
4.8
4.4
4.0
3.6
3.2
δ
H, ppm
CF3
(b)
(CF2)4
−
74
−
82
−
90
−
98
−
106
−
114
−
122
−130
F, ppm
δ
1
19
Fig. 1. (a) H and (b) F NMR spectra of polymer I.
ring is split into two peaks, which confirms the regioꢀ that, although the molecular weights of the polymers
random character of the bond. Regioregularity (the obtained in both solvents are almost equal, the polyꢀ
ratio of headꢀtoꢀtail, headꢀtoꢀhead, or tailꢀtoꢀtail) was dispersity of polymers obtained in scꢀCО2 is much
calculated from the intensity ratio of two peaks of the
methylene group directly bound to the thiophene ring.
As it was expected, the majority of polymers obtained
in scꢀCО2 have the regiorandom bond character. The
same values were also obtained for PFTs synthesized in
chloroform, which indicates the similar effect of solꢀ
vents on the stereoregularity of polymerization.
higher than that of polymers obtained in chloroform.
This fact may result from the different solubility of the
monomers in scꢀCО2 and chloroform.
All the polymers are soluble in common organic
solvents such as DMF, toluene, THF, chloroform, and
acetone. The thermal characteristics of polyꢀ
thiophenes I–V were studied by TMA and TGA, the
results are given in Table 3. The glass transition temꢀ
The molecular weights and polydispersity of polyꢀ
mers
the range 3950–5880 and 8040–12420 (Mn), 21720–
11200 and 19880–38120 w), 2.71–3.69 and 2.47–
3.07 (Mw Mn), respectively (Table 3). Table 3 shows perature of 10% weight loss (Т10%) determined by TGA
I–V obtained in scꢀCО2 and chloroform vary in
peratures of the polymers (Тg) determined from TMA
curves are rather low and fall in the range of 54
–82°С.
(M
The polymers show good thermal stability. The temꢀ
/
DOKLADY CHEMISTRY Vol. 443
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2012

104
KESHTOV et al.
Table 2. Spectral characteristics of polythiophenes of general formula
O
O
R
n
S
NMR; δ, ppm
Polymer
R
IR, cm–1
1758
λ
abs, nm
λ
fl, nm
1Н
19F
I
CH2(CF2)4CF3
6.72–7.25(m,1Н) –126.44 (2F)
4.51–4.77(m,2Н) –123.74 (2F)
3.71–4.00(m,2Н) –123.11 (2F)
–119.80 (2F)
402
526
–80.93 (CF3)
II
CH2(CF2)5CF3
(CH2)3(CF2)5CF3
CH2(CF2)7CF3
(CH2)2(CF2)7CF3
1762
1740
1757
1737
6.87–7.21(m,1Н) –126.31 (2F)
4.41–4.79(m,2Н) –123.51 (2F)
3.50–3.97(m,2Н) –122.97 (2F)
–122.26 (2F)
386
381
395
398
512
506
525
525
–119.73 (2F)
–80.96 (CF3)
III
IV
V
6.75–7.25(m,1Н) –126.37 (2F)
4.10–4.32(m,2Н) –123.54 (2F)
3.52–3.91(m,2Н) –123.07 (2F)
1.18–2.31(m,4Н) –122.12 (2F)
–114.52 (2F)
–81.04 (CF3)
6.67–7.23(m,1Н) –126.25 (2F)
4.48–4.75(m,2Н) –123.44 (2F)
3.51–3.92(m,2Н) –122.35 (2F)
–122.04 (6F)
–119.72 (2F)
–80.83 (CF3)
6.60–7.25(m,1Н) –126.26 (2F)
4.15–4.53(m,2Н) –123.62 (2F)
3.82–3.93(m,2Н) –122.26 (2F)
2.28–2.58(m,2Н) –122.05 (6F)
–113.73 (2F)
–80.89 (CF3)
in argon atmosphere and in air are within 248–294 absorption spectra of polymers
I
–
V
obtained in scꢀ
= 381–402 nm and shifted to
the blue region as compared with poly(3ꢀoctylꢀ
thiophene) ( = 437 nm) due to decrease in the conꢀ
and 270 300 for the polymers obtained in scꢀCО2
–
°С
C
О2 are in the range of
λ
and chloroform, respectively. The data of Table 3 indiꢀ
cate that the introduction of additional CF2 groups in to
the polymer chain leads to increase in the glass transiꢀ
tion temperature and thermal stability of the polymers.
λ
jugation length of poly(fluoroalkyl 3ꢀthienylacetate)
chain. These spectra are identical to those of polymers
I–V obtained in chloroform. All the polymers exhibit
Ultraviolet absorption and fluorescence spectra
provide further understanding of the conjugation
extent of the polymer, the structure and effect of fluoꢀ
roalkyl ester substituents on the polymer chain and
electronic effects in PFT obtained in scꢀCО2. The
photophysical properties of the polymers were studied
by UV and fluorescence spectroscopy, the results are
presented in Fig. 2 and Table 2. The maxima of
fluorescence in the blue region with emission maxima
in the range 506–526 nm (Fig. 2). There is a marked
difference in the Stokes shift. Fluorescence maxima
are shifted to the right by 124–130 nm relative to the
absorption maxima with minimal overlapping. Such a
trend in fluorescence takes place for the polymers
obtained in both scꢀCО2 and chloroform.
DOKLADY CHEMISTRY Vol. 443
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CONJUGATED POLY(FLUOROALKYL 3ꢀTHIENYLACETATE)S
105
Table 3. Certain characteristics of obtained in scꢀCO2 polythiophenes of general formula
O
O
R
n
S
T10%,
C c
(ТHF)
°
Tg, °C
(DМF)
Yield, % b
Mn
Mw
Mw/Mn
Polymer
R
Solvent
285
ꢀꢀꢀꢀꢀꢀ
I a
I
CH2(CF2)4CF3
CH2(CF2)4CF3
CHCl3
scꢀCO2
86
73
9230
5810
25780
19180
2.77
3.30
82
305
270
ꢀꢀꢀꢀꢀꢀ
74
285
303
ꢀꢀꢀꢀꢀꢀ
II a
II
CH2(CF2)5CF3
CH2(CF2)5CF3
CHCl3
scꢀCO2
91
79
12420
5880
38120
21720
3.07
3.69
82
79
317
294
ꢀꢀꢀꢀꢀꢀ
300
282
ꢀꢀꢀꢀꢀꢀ
III a
III
(CH2)3(CF2)5CF3 CHCl3
(CH2)3(CF2)5CF3 scꢀCO2
80
71
11730
5070
31670
17240
2.70
3.40
62
58
305
263
ꢀꢀꢀꢀꢀꢀ
280
275
ꢀꢀꢀꢀꢀꢀ
IV a
IV
CH2(CF2)7CF3
CH2(CF2)7CF3
CHCl3
scꢀCO2
80
70
8040
4140
19880
11200
2.47
2.71
72
63
280
260
ꢀꢀꢀꢀꢀꢀ
278
260
ꢀꢀꢀꢀꢀꢀ
V a
V
(CH2)2(CF2)7CF3 CHCl3
(CH2)2(CF2)7CF3 scꢀCO2
82
72
8430
3950
24370
13230
2.89
3.35
68
63
295
248
ꢀꢀꢀꢀꢀꢀ
270
a
b
c
Polymers were obtained in chloroform.
Polymerization conditions: 2 h at 40°C at monomer to catalyst ratio of 1 : 4.
The temperature of 10% weight loss of polymers in air in the numerator and that in argon in the denominator.
Experimental results show that scꢀCО2 has no
effect on the conformational distribution of polymers
in the course of polymerization.
Thus, we have prepared a series of novel fluoroalkyl
esterꢀcontaining polythiophenes by oxidative
polymerization in scꢀCО2 and chloroform. The polyꢀ
I–V
1.00
0.75
0.50
0.25
0
1000
I
II
III
IV
V
750
500
250
0
300
350
400
450
500
, nm
550
600
650
700
λ
–5
Fig. 2. Absorption and fluorescence spectra of polymers
DOKLADY CHEMISTRY Vol. 443 Part 2 2012
I
–V
in chloroform (
с
= 10 M).

106
KESHTOV et al.
3. Keshtov, M.L., Mal’tsev, E.I., Pozin, S.I., and
Khokhlov, A.R., Vysokomol. Soedin. Ser. A, 2010,
vol. 52, no. 12, pp. 2203–2208.
mers were obtained in both solvents in high yields and
with high molecular weights.
The properties of the polymers obtained in scꢀCО2
,
4. Keshtov, M.L., Venidiktova, O.V., Barachevskii, V.A.,
et al., Vysokomol. Soedin. Ser. A, 2009, vo. 51, no. 7,
pp. 1269–1277.
such as molecular weight, polydispersity, conjugation,
UV absorption, are similar to the properties of
poly(fluoroalkyl 3ꢀthienylacetate)s obtained in chloꢀ
roform. The unique combination of fluoroalkyl and
carbonyl groups makes the poly(fluoroalkyl 3ꢀthienyꢀ
lacetate)s highly soluble in scꢀCО2. Our studies show
that scꢀCО2 is an alternative promising solvent for the
oxidative polymerization of fluoroalkyl 3ꢀthienylaceꢀ
tates.
5. Keshtov, M.L., Grigor’ev, T.E., and Khokhlov, A.R.,
Vysokomol. Soedin. Ser. A, 2009, vol. 51, no. 12,
pp. 2178–2189.
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pp. 2952–2958.
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ACKNOWLEDGMENTS
9. Keshtov, M.L., Mal’tsev, E.I., Lopatin, A.M., et al.,
This work was supported by the Division of Chemꢀ
istry and Material Science, Russian Academy of Sciꢀ
ences (Basic Research Programs OKhꢀ3 “Design and
Study of Macromolecules and Macromolecular Strucꢀ
tures of New Generations” and OKhꢀ2 “Design of
New Metallic, Ceramic, Glass, Polymeric, and Comꢀ
posite Materials”).
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DOKLADY CHEMISTRY Vol. 443
Part 2
2012