Int. J. Mol. Sci. 2008, 9, 383-393
International Journal of
© 2008 by MDPI
Full Research Paper
Synthesis and Characterization of Polyacetylene with Side-chain
Banu Koz, Baris Kiskan and Yusuf Yagci *
Istanbul Technical University, Department of Chemistry, Maslak 34469, Istanbul, Turkey
Tel. +90 212 285 6325 or 3241; Fax: +90 212 285 6169 or 6386; E-mails: firstname.lastname@example.org;
* Author to whom correspondence should be addressed.
Received: 30 November 2007; in revised form: 30 January 2008 / Accepted: 29 February 2008 /
Published: 18 March 2008
Abstract: A new polyacetylene derivative with electroactive thiophene substituent, namely
poly(2-methylbut-2-enyl thiophene-3-carboxylate) was synthesized and characterized. For
this purpose, novel acetylene monomer was synthesized by the reaction of 3-
thiophenecarboxylic acid with propargyl bromide and polymerized with a Rh catalyst to
give the corresponding polymer. The chemical structure of the polymer was characterized
to comprise the conjugated backbone and electroactive thiophene side group. UV spectral
changes of the polymer with temperature were also studied. The polymer exhibited better
thermal stability than the unsubstituted polyacetylenes.
Keywords: Polyacetylene, Helical polymer, Conjugated polymer, Thiophene.
It is known that substituted acetylenes polymerize with transition metal catalysts [1-4]. Among
various catalysts used, Rh based catalysts received particular interest as they efficiently polymerize
mono-substituted acetylenes, especially phenylacetylene [4-12]. Rh catalysts are also capable of
polymerizing monomers with polar substituents such as propiolic esters [13-18] and propargyl amide
[19-22]. Moreover, polymerization is tolerant to protic solvents such as alcohols [5, 7], amines , and
even water  and ionic liquids  and selectively give stereo-regular polymers with cis-transoid
isomer having helical main chain [4-6]. Providing that the helical sense of the π-conjugated polymers
Int. J. Mol. Sci. 2008, 9
is controlled, the polymer backbone becomes optically active [23-26]. The backbone chirality of the
π-conjugated polymers can be detected directly by measuring their CD behavior, since the main-chain
itself is a chromophore. Meanwhile, substituted polyacetylenes exhibit unique properties such as
semi-conductivity, nonlinear optical properties, and high gas permeability due to the conjugated main
chain and rigid molecular structure [1, 27-29]. However, notoriously intractable and thermally unstable
nature of polyacetylenes is deterrent for their potential use in technological applications. Attachment of
aromatic pendants to the polyacetylene backbone is one way to overcome problems associated with
intractability and thermal degradation [4, 30-38]. For example, poly-(1-phenyl-1-alkyne)s are soluble
in common solvents and do not decompose at elevated temperatures for a prolonged period of time
. It is expected that incorporation of various substituents to acetylenes and their subsequent
polymerization may lead to the conjugated polymers with new properties. Polymers containing
thiophene units have been the subject of extensive research for more than 25 years. Polythiophenes are
interesting for their not only electrical properties, but also electrophysical, magnetic, liquid crystalline
and optical properties [39, 40]. However, polythiophenes suffer from the poor mechanical and physical
properties. These properties can be improved by incorporating thiophene moieties into other insulating
polymers and subsequent polymerization through these electroactive thiophene groups [41-43].
Various controlled [44-47] and conventional  polymerization methods to incorporate thiophene
groups into polymers have recently been reported. It seemed therefore appropriate to synthesize acety-
lene with electroactive thiophene group. The corresponding polymers may form helical thiophene
strands as well as a helical polyacetylene main chain possessing unique electronic and photonic
functions. In this study, we report synthesis of acetylene with side-chain thiophene moiety and its
polymerization with Rh catalyst in conjunction with co-catalyst. Structural, thermal and
electrochemical characterizations of the monomer and corresponding polymer were performed by
FT-IR, 1H-NMR, UV, TGA and CV measurements.
Results and Discussions
The synthetic strategy used to prepare propargyl thiophene, as monomer, based on heterogeneous
esterification reaction between 3-thiophenecarboxylic acid and propargyl bromide in basic medium
Scheme 1. Synthesis and Polymerization of Propargyl-thiophene by Using Rh(nbd)Cl2].
The chemical structure of propargyl thiophene was confirmed by both FT-IR and 1H-NMR
spectroscopy. As can be seen from Figure 1, 1H-NMR spectrum exhibits structural characteristics of
both acetylene and thiophene units. The signal of terminal acetylene proton emerges as triplet at
Int. J. Mol. Sci. 2008, 9
2.50 ppm with 2.4 Hz J, and the two C3 protons of the propargyl part were noted as a doublet at
4.86 ppm with 2.5 Hz J. Additionally, C2, C4 and C5 protons of thiophene heterocycle appear at
8.16 ppm as doublet of doublet (dd) with 4J13: 3 Hz and 5J14: 1.3 Hz, at 7.30 ppm as dd, 3J34: 5.9 Hz
and 4J13: 3 Hz, at 7.53 ppm as dd, 3J34: 5.2 Hz and 5J14: 1.3 Hz, respectively.
Figure 1. 1H NMR spectrum of propargyl-thiophene.
The FT-IR spectrum shown in Figure 2 (b) also establishes the structure of the monomer. Accor-
dingly, diagnostic stretching vibrations of ester carbonyl, aromatic C-H and terminal acetylenic C-H
and C ≡ C bands appear at 1716 cm-1, 3112 cm-1, 3292 cm-1 and 2128 cm-1, respectively. Moreover,
sp2 C-O and sp C-O stretching vibrations observed at 1246 and 1095 cm-1 are additional support for the
Propargyl thiophene is expected to undergo polymerization with Rh catalyst through the acetylenic
group as depicted in Scheme 1. The Rh-catalyzed polymerization reaction in toluene proceeded
smoothly at ambient temperature and gave the expected polyacetylene in moderate yields after
precipitation. In this polymerization, (bicyclo[2,2,1]hepta-2,5-diene)chlororhodium(I) dimer,
abbreviated as [(nbd)RhCl]2, was selected as the catalyst due to its widespread use in related
polymerizations. The results of polymerizations under different experimental conditions are given in
Table 1: Polymerizationa of acetylene-thiophene by Rh catalysts in conjunctiona with
a [M]o = 0.2 M, [Rh]= 2 mM, [Co-catalyst] =20mM, 30 oC, 24 h; b Determined by GPC according to
Int. J. Mol. Sci. 2008, 9
As can be seen, polymerization with all co-catalysts used resulted in polymers with relatively low
yields and molecular weights. Limited chain growth is probably due to the inefficient ligation of
co-catalysts and monomer together to the growing species [49, 50]. The chemical structure of the
polyacetylene obtained was confirmed by both FT-IR and 1H-NMR spectroscopy. In the FT-IR
spectrum (Figure 2), the disappearance of the acetylenic C-H and C ≡ C stretching vibrations at
3292 cm-1 at 2128 cm-1, respectively, was clearly noted. Also, carbonyl C=O stretching at 1716 cm-1
and sp2 C-O and sp C-O stretching vibrations at 1246, 1095 cm-1 are evidencing the retention of ester
group after the polymerization.
Figure 2. FT-IR spectra of (a) PAT-2 and (b) propargyl-thiophene.
Further analysis of the polymer by 1H-NMR as presented in Figure 3 indicated the characteristic
peak for cisoid =C-H proton at 6.4 ppm. Additionally, the two protons, neighboring ester group and
double bond emerge at 4.75 ppm with a slight shift compared to C3 protons of the precursor propargyl
unit (see Figure 1). This shift clearly suggests the transformation of triple bond to double bond. The
retention of aromatic peaks was also noted.
Figure 3. 1H NMR spectrum of polymer PAT-2.
Int. J. Mol. Sci. 2008, 9
Electrochemical property of the polymer was investigated by cyclic voltammetry (CV). Reversible
redox potentials and LUMO energy values based on the value of 4.8 eV for ferrocene (FC) with respect
to zero vacuum level [51, 52] were determined and summarized in Table 2. As can be seen
poly(acetylene-thiophene) displays two cathodic peaks and two anodic peaks. The reduction potentials
are 0.71 V and 1.16 V and LUMO is 4.09 eV. These results clearly indicate the electroactivity of the
polymer. It is worth to mention that no detectable redox peaks were observed with the polymers
possessing non-conjugated backbone i.e., methacrylate and maleimide polymers with side chain
thiophene unit [42-43]. However, they become electroactive only in the presence of bare monomers
such as thiophene and pyrrole. The enhanced activity in our case may be due to the conjugated
backbone. In this connection, it should be pointed out that polyacetylenes with directly attached
thiophene units were previously reported. However, no information on their electrochemical properties
was given .
Table 2. Cylic voltammetrya data and LUMO energy values of poly(acetylene thiophene)
in dichloromethane. E1/2/V vs. Fc is the reduction potential versus ferrocene electrode
(E1/2/V vs. Fc= (E1/2/V vs. Ag/AgCl)-(EFc/V vs. Ag/AgCl)).
Electrode Epc/V Epa/V
E1/2/V vs. Fc
a Supporting electrolyte is 0.1 M tetrabutylammonium perchlorate (TBAP). [PAT-2] = 6.6 g/l.
Figure 4. UV-vis spectral changes of PAT-2 from 5 to 55 0C measured in CHCl3
[PAT-2]= 1.8 x 10-5.
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Figure 4 shows the UV spectral changes of the polymer solution in CHCl3 with temperature. As can be
seen, the absorbance at lower wavelengths increases by increasing the temperature probably due to the
transformation to a non-ordered structure. Thermal stability of the poly(acetylene-thiophene) (PAT-2)
was investigated by thermal gravimetric analysis (TGA) under nitrogen exposure. The TGA profile of
the polymer is shown in Figure 5 and the results are summarized in Table 3. It is well known that
mono-substituted polyacetylenes are generally thermally unstable. Typically, poly(1-hexyne) starts to
lose its weight at ~ 150 0C. Interestingly, the temperature for 5% weight loss is 230 oC for PAT-2. In
fact, this value is slightly lower than that of the another aromatic substitutued poly(phenyl acetylene)
(T= ~ 264 oC) [35-38].
Table 3. Thermal properties of polyacetylenes.
T5%a (ºC) T10%b (°C)
Ycd at 500°C (%)
aT5%: The temperature for which the weight loss is 5%; bT10%: The temperature for which the weight loss is 10%; cTd max:
Maximum weight loss temperature; dYc: Char yields
Figure 5. TGA thermogram of PAT-2 (a) recorded under nitrogen at a heating rate of 10
0C/min., (b) derivative of curve (a).
In conclusion, a new conjugated polymer, polyacetylene, with electroactive active thiophene groups
was synthesized by using a Rh catalyst and characterized. The polymer structure, electrochemical and
thermal properties were characterized by various instrumental methods. The new polymer is expected
to undergo electropolymerization leading to crosslinked polymers having conjugated segments in both
main- and side-chain with enhanced conductivities and helical tunnels in the structure. Further studies
in this line are now in progress.
Int. J. Mol. Sci. 2008, 9
3-Thiophenecarboxylic acid % 99 (Acros), propargyl bromide solution in toluene ~ %80 (Fluka), te-
trabutylammonium bromide (+ %99) (Acros), (bicyclo[2,2,1]hepta-2,5-diene)chlororhodium(I) dimer
([(nbd)RhCl]2 )≥ %98 (Fluka), diisopropylamine ≥ % 99 (Merck), triethylamine ≥ % 99.5 (Aldrich),
were purchased and used as received. Solvents used for polymerization were purified before usage by
the standard drying and distillation procedures.
The molecular weights of polymers were measured by GPC at 30 0C with an Agilent instrument
(Model 1100) consisting of a pump, refractive index and UV detectors and four Waters Styragel col-
umns (HR 5E, HR 4E, HR 3, and HR 2) eluent THF, flow rate of 0.3 mL/min and calibrated with po-
lystyrene standards. Toluene was used as an internal standard. Data analyses were performed with PL
caliber Software. 1H NMR spectra were recorded on a Bruker 250 Mhz spectrometer using CDCl3 as
solvent and tetramethylsilane as the internal standard. FT-IR spectra were measured on Perkin-Elmer
FT-IR Spectrum One spectrometer. Thermal gravimetric analysis (TGA) was performed on Perkin-
Elmer Diamond TA/TGA with a heating rate of 10 0C min under nitrogen flow. Cylic voltammetry
measurements were carried out using a Princeton Applied Research Model 2263. Cylic voltammetry in
dichloromethane was performed using a 3-electrode cell (BASI model solid cell stand) with a polished
2mm sized Pt disc electrode as working electrode, a Pt wire counter electrode and an Ag/AgCl refer-
ence electrode, with a solution of polymer (6.6 g/l) and tetrabutylammonium perchlorate (TBAP,0.1
M) in CH2Cl2. All solutions were purged with nitrogen for at least 10 min before starting the mea-
surements. UV-vis spectra were recorded on JASCO V-530 UV-vis spectro photometer.
In a 250 mL flask, of 3-thiophenecarboxylic acid (2.0 g, 15 mmol) was dissolved in 100 mL of 0.1
N NaOH. The mixture was heated at 50 0C until a clear solution was formed. To this solution, tetrabu-
tylammonium bromide (0.50 g, 1.55 mmol) was added as a phase transfer catalyst. Then, a solution of
propargylbromide (2.0 g, 17 mmol) in 20 mL of toluene was added portion wise. The mixture was kept
stirring at 60 0C for 24 h. At the end of this period, it was cooled to afford solid. Additonally, the re-
maining toluene layer was separated and washed repeatedly with %2 NaOH (200 mL, 0.1 N) and with
water. Evaporating toluene afforded extra solid.
Polymerization was carried out under N2 atmosphere in a Schlenk tube equipped with a three-way
stopcock. A typical polymerization procedure is as follows: A toluene solution (2.0 mL) of 1 (1 mmol)
was added to a toluene solution (3.0 mL) of [(nbd)RhCl]2 (10-3 mmol ) with co-catalyst diisopropyla-
mine (10-2 mmol). Polymerization was carried out at 30 0C for 24 h.
Int. J. Mol. Sci. 2008, 9
The authors would like to thank Istanbul Technical University, Research Fund for financial support.
One of the authors (B.Koz) would like to thank Tubitak (Turkish Scientific and Technologic Research
Council) for the financial support by means of a postdoctoral fellowship.
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