The composites of silver with globular or nanotubular polypyrrole: The control of silver content

Synthetic Metals 209 (2015) 105–111

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The composites of silver with globular or nanotubular polypyrrole: The control of silver content nkováb , Elizaveta Alekseevaa , Patrycja Boberb , Miroslava Trchováb , Ivana Šede a b, Jan Prokeš , Jaroslav Stejskal * a b

Charles University in Prague, Faculty of Mathematics and Physics, 180 00 Prague 8, Czech Republic Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic

A R T I C L E I N F O

A B S T R A C T

Article history: Received 12 May 2015 Received in revised form 29 June 2015 Accepted 3 July 2015 Available online xxx

Polypyrrole/silver composites were prepared by chemical polymerization of pyrrole using a mixture of oxidants, silver nitrate and iron(III) nitrate, in aqueous medium at room temperature. The silver content from 0 to 78 wt.% was controlled by varying the proportions of both oxidants. Polypyrrole had globular morphology or was obtained as nanotubes in the presence of methyl orange. The morphology of composites was confirmed by transmission electron microscopy. Silver was present as a larger objects of 150–200 nm size in globular polypyrrole morphologies or as 70 nm nanoparticles accompanying the polypyrrole nanotubes. The molecular structure is discussed on the basis of infrared and Raman spectra. Conductivity of the composites of silver with polypyrrole nanotubes is 10–30 S cm 1. For composites with globular polypyrrole, the conductivity was lower, 0.17–0.7 S cm 1. ã 2015 Elsevier B.V. All rights reserved.

Keywords: Conducting polymer Polypyrrole Nanotubes Silver nanoparticles

1. Introduction Since the Nobel Prize was awarded in 2000 “for the discovery and development of conducting polymers” [1], many conducting polymers have received increasing interest [2]. Early studies have illustrated the potential of conducting polymers to compete with metals in the conduction of electric current, and conductivities comparable to those of metals have been reported [3]. Even though the conductivity is still regarded as the most important parameter, other properties came to the forefront. Conducting polymers, mainly polyaniline, polypyrrole (PPy) and poly(3,4ethylenedioxythiophene), possess the ability to respond various stimuli by the change in their optical, chemical and electrical properties, which can be useful in many applications [4–7]. Among conducting polymers, PPy is frequently investigated due to its good environmental stability, biocompatibility [8,9], redox behavior [10], and high conductivity [11]. Polypyrrole has been studied for the immobilization of enzymes, antibodies, and nucleic acids [12]. It is also suitable as a substrate for cell attachment and proliferation and has excellent biocompatibility in vivo [13–15]. In addition, PPy can be used as conducting filler or as a matrix for the preparation of conducting composites [16–18]. Polypyrrole is usually prepared by the oxidation of pyrrole with iron(III) chloride

* Corresponding author. E-mail address: [email protected] (J. Stejskal). http://dx.doi.org/10.1016/j.synthmet.2015.07.003 0379-6779/ ã 2015 Elsevier B.V. All rights reserved.

[11,19]. Other inorganic oxidants have also been successfully tested, such as ammonium peroxydisulfate [20–22] or cerium(IV) sulfate [23,24]. Currently, silver nitrate became of interest because such oxidation of pyrrole leads to PPy/silver composites [21,22,25–31] (Fig. 1). The ability of PPy to reduce silver ions to metallic silver has also been reported [32]. Polypyrrole/silver composites are expected to combine materials properties of polymers and electrical properties of metals [33]. Incorporation of silver nanoparticles to PPy may improve the conductivity of the resulting composites by ca. 3–4 orders of magnitude [11]. Polypyrrole is usually obtained in globular morphology [32], however, the use of structure-guiding agent, methyl orange (MO), has led to nanotubes [19,34]. Globular PPy is difficult to process by compression to pellets that are needed for the electrical characterization. On the contrary, one-dimensional structures, such as nanotubes, produce pellets with good mechanical properties. They are thus better suited for the investigation of conductivity and charge transport and could be of benefit in many applications [35–37]. In addition, the conductivity of PPy nanotubes, 60 S cm 1, is higher than that of the globular form [34]. The impact of MO on the morphology of PPy has been reported for the first time by Yang et al. [38] in 2005, where the creation of PPy nanostructures was obtain due to self-degraded template formed by MO with iron(III) chloride. The synthesis of PPy nanotubes in the presence of MO has later been reported in literature many times [32,39,40–45]. More general mechanisms of nanotubular formation have recently been proposed [19,34].

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2.2. Characterization The transmission electron microscope (TEM) JEOL JEM 2000 FX was used to assess the morphology of the samples. The silver content in the composite materials was determined as an ash. Thermo Nicolet NEXUS 870 FTIR Spectrometer in an H2Opurged environment with DTGS detector in the wavelength range from 400 to 4000 cm 1 has been used for measurement of the infrared spectra. Measurements of the powdered samples were performed ex situ in the transmission mode in potassium bromide pellets. Raman spectra excited with HeNe 633 nm were collected on a Renishaw inVia Reflex Raman microspectrometer. The scattered light was analyzed by the spectroscope with holographic grating 1800 mm 1. A Peltier-cooled CCD detector (576  384 pixels) registered the dispersed light. The room temperature conductivity of globular and nanotubular PPy was determined by a four-point method in the van der Pauw arrangement using a Keithley 220 Programmable Current Source, a multimeter as a voltmeter and a scanner equipped with a matrix card. The composite powders were compressed at 70 kN by a manual hydraulic press to the pellets 13 mm in diameter and 1 mm thick. Fig. 1. The oxidation of pyrrole with silver nitrate to polypyrrole/silver composites. Nitric acid is a by-product.

3. Results and discussion 3.1. Polypyrrole and silver morphology

We report here a facile single-step approach of the preparation of conducting PPy/silver composites in globular and nanotubular forms. The use of mixed oxidants, silver nitrate and iron(III) nitrate [46] in various proportions, allowed to control the silver content from 0 to 76 wt.%. This approach has successfully been earlier used in the preparation of polyaniline/silver composites [47,33]. Special attention was paid to the investigation of the conductivity of the hybrid PPy/silver composites. 2. Experimental Two series of syntheses have been performed. In the first series, a fixed concentration of pyrrole was oxidized with a mixture of oxidants, silver nitrate and iron(III) nitrate. The total molar concentration of oxidants was kept constant but their proportion was varied, the variable being the fraction of silver nitrate to total concentration of oxidants, x = [AgNO3]/([AgNO3] + [Fe(NO3)3]). The higher was the ratio x, the higher is expected to be the content of silver in the resulting PPy/silver composites. The second series was made in the same manner but in the presence of methyl orange, which should stimulate the formation of nanotubular morphology of PPy. 2.1. Synthesis Globular PPy was prepared by the chemical polymerization of 0.05 M pyrrole (98%, Sigma–Aldrich) with iron(III) nitrate nonahydrate (Sigma–Aldrich) or silver nitrate (Lach-Ner, Czech Republic) or their mixtures in various proportions x, from x = 0 for the oxidation with 0.05 M iron(III) nitrate alone to x = 1 for 0.05 M silver nitrate as oxidant. Both the monomer and the oxidants were separately dissolved in water and then mixed. The reaction mixture was stirred with a magnetic bar for 6 h and then left to stand for 7 days at room temperature. The solids were isolated by filtration, rinsed with ethanol, and dried in air, and then over silica gel. Polypyrrole nanotubes were synthesized in a similar condition in the presence of methyl orange (sodium 4-[(4-dimethylamino) phenylazo]benzenesulfonate (Penta, Czech Republic). The pyrroleto-MO mole ratio was 10.

The oxidation of pyrrole with mixed oxidants in the presence of MO leads to nanotubular morphology of PPy moiety (Fig. 2). Nanotubes have a 100 nm diameter and a length of a few hundred nm estimated by TEM. Polypyrrole prepared in the absence of MO has globular morphology (Fig. 2). Silver according to analytical analysis is present in all composites prepared by oxidation of pyrrole with silver nitrate or mixture of both oxidants. In the case of globular PPy/silver composites, it can be seen that the silver is present as larger objects of 200 nm size. Also large silver particles are visible in PPy/silver nanotubes prepared by silver nitrate alone, x = 1, uniformly deposited throughout the PPy matrix (Fig. 2). 3.2. Yield and silver content The yield of both the globular and nanotubular PPy/silver composites increases with increasing fraction of silver nitrate, x, in the mixture of oxidants (Fig. 3). This corresponds to the increasing content of silver in the composites. For the oxidation with silver nitrate alone, the stoichiometry (Fig. 1) predicts the yield 2.18 g composite per 1 g of pyrrole and silver content 73.8 wt.%. This is not in agreement with the experimental result (Fig. 3) for the globular samples prepared in the absence of methyl orange. It is important observation that the yield of composites prepared in the presence of methyl orange is systematically higher (Fig. 3). This indicates that methyl orange has to be incorporated into the composites either by physical entrapment inside the nanotubes or as polypyrrole counter-ions. The nature of the effect, which is independent of the oxidant type, is under investigation in separate experiments. The content of silver in the PPy/silver composites is close to the theoretical value 76 wt.%. The ratio of silver in the composites depends directly on the mole fraction of silver nitrate in the oxidant mixture (Fig. 4). 3.3. FTIR spectra Infrared spectra of globular PPy/silver composites prepared without MO exhibit the main peaks of PPy (Fig. 5) [11,20]. We observe

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Fig. 2. Transmission electron micrographs of the globular and nanotubular polypyrrole/silver composites prepared with the oxidant proportion x = 0 (iron(III) nitrate oxidant alone), x = 0.5 (mixed oxidants) and x = 1.0 (silver nitrate oxidant alone). Left column—globular, right column—nanotubular polypyrrole.

the band at 1538 cm 1 of C C stretching vibrations in the pyrrole ring, and the band at about 1470 cm 1 of the C N stretching vibrations in the ring. In all spectra we detect a sharp peak situated at 1383 cm 1 with a shoulder at 1350 cm 1 of nitrate anions which act as counterions in PPy salt [48]. The broad band with maximum at about 1290 cm 1 belongs to C H or C N in-plane deformation modes, and a maximum at 1165 cm 1 is observed in the region of the breathing vibrations of the pyrrole ring. The band at 1035 cm 1 is assigned to the C H and N H in-plane deformation vibrations, and the peaks at about 900 and 780 cm 1 to the C H out-of-plane deformation vibrations of the ring. The positions and shape of the bands in the infrared spectra are independent of the oxidant used. Globular PPy prepared with iron(III) nitrate was much better to disperse in potassium bromide

pellets than in case of compact stone-like structure of PPy prepared with silver nitrate. Absorption of the PPy/silver as-produced composites salts was very small, and the measured spectra contain relatively strong absorption bands in the region of stretching and bending vibrations of water molecules at about 3425 and 1635 cm 1, respectively (Fig. 5) and of the stretching vibrations of aliphatic hydrocarbons at about 2920 cm 1 which come from bromide pellets. They increase with increasing amount of silver nitrate as oxidant. As the peak of nitrate anions is much higher for higher amount of iron(III) nitrate, their presence in the composite probably influences a better dispersion in potassium bromide pellet. Infrared spectra of nanotubular PPy/silver composites prepared in presence of MO exhibit in some cases the main peaks of PPy

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2.4

Y,g

1.8 globular

nanotubular

1.2

0.6 0

20

40

60

80

100

x, mol% AgNO3 Fig. 3. Dependence of the yield, Y, of composite per 1 g of pyrrole of nanotubular (full squares) and globular polypyrrole/silver composites (open squares) on the mole fraction of silver nitrate in the oxidant mixture, x.

(for x = 20, 50), in other cases the spectrum contains the peaks of MO (for x = 80, peaks of MO are marked with asterisks in Fig. 6), or the spectra correspond to the spectrum of neat MO (for x = 0 or 100). This observation can be explained by the fact, that MO is in-homogenously dispersed in the samples, and small amount of sample used in FTIR analysis is taken from different part of them. This hypothesis is supported by the Raman analysis (see Section 3.4). MO is present in the composite in the acid form (Fig. 6). MO observed in nanotubular PPy by infrared spectroscopy corresponds most probably to the solid precipitated structures which are produced when MO interacts with oxidant. Such objects act as templates in the growth of PPy nanotubes [34]. In cases when the spectra of nanotubular samples correspond to the spectrum of PPy, the peaks are practically at the same positions as in the case of globular PPy (compare with Fig. 5), and the strong peak of nitrate anions at 1383 cm 1 is well detected in the spectra. In cases when the spectra correspond to pure MO, nitrate counter-ions are probably replaced by MO which interacts with PPy. 3.4. Raman spectra

80

60 globular

40

20

0

20

40

60

80

100

x, mol % AgNO3 Fig. 4. Dependence of the silver content, wAg, on the nanotubular (full squares) and globular polypyrrole/silver composites (open squares) on the mole fraction of silver nitrate in the oxidant mixture, x.

Globular

100

900 780 675

100

963

1035

FTIR in KBr

x=

Absorbance

x5

1635

2920

x=

1538 1470 1383 1350 1290 1165

3425

Absorbance

Nanotubular

FTIR in KBr

80 50

80

*

50

*

780

0

1538 1470 1383 1290 1165 1035

wAg, wt. %

nanotubular

In the Raman microscope it is observed that the samples of PPy/silver composites are inhomogeneous at micrometre level. In the globular and nanotubular samples we observe dark and bright regions. This observation is reflected in their Raman spectra. The spectra measured in the dark regions correspond to PPy. The bright regions correspond to silver particles and MO. Raman spectra of globular PPy/silver composites exhibit the main peaks of PPy which are practically at the same positions for various composition of oxidant mixture (Fig. 7) [49]. Only small differences in the relative intensities of some peaks are detected. We observe the peaks at 1585 cm 1 of C C stretching vibrations in the pyrrole ring, the peak at 1382 cm 1 of C H and N H in-plane bending vibrations, at 1315 cm 1 of C C stretching vibrations, at 1248 cm 1 of antisymmetric C H in-plane deformation vibrations, at 1085 cm 1 of out-of-plane C H and N H deformation vibrations, and the peak at 931 cm 1 of C C deformation vibrations. Raman spectra of globular PPy/silver composites prepared without MO measured in bright regions are enhanced and they exhibit in some cases a strong fluorescence. These regions correspond to the silver particles and the low-molecular-weight products of pyrrole oxidation. Raman spectra of nanotubular PPy/silver composites prepared in presence of MO and recorded with a 633 nm excitation laser

*

20

20

0 0 MO.HCl

4000

3500

3000

2500

2000

1500

1000

500

–1

4000

3500

3000

2500

2000

Wavenumbers, cm

1500

1000

500

–1

Wavenumbers, cm

Fig. 5. FTIR spectra of globular polypyrrole/silver composites with various composition of oxidant mixture, x.

Fig. 6. FTIR spectra of nanotubular polypyrrole/silver composites with various composition of oxidant mixture, x. The spectrum of pure MO
HCl is shown for comparison.

E. Alekseeva et al. / Synthetic Metals 209 (2015) 105–111

x=50

x=100

nanotubular

10 –1

Intensity

x=

Raman exc. 633 nm 1085 1055 931

1585

1382 1315 1248

dark regions

Globular

109

σ, S cm

100 80

1

50

globular

20 0

3000

2500

0.1

2000

1500

1000

500

–1

Wavenumbers, cm

(Fig. 8) exhibit the main peaks at 1588, 1392, 1319, 1245, 1048 and 926 cm 1, which are only slightly shifted in comparison to their positions in the spectrum of globular PPy. They differ in the region of the peaks situated at 1045 and 925 cm 1, which reflects their nanotubular structure and the interaction with MO. Raman spectra of nanotubular PPy/silver composites prepared with MO and measured in bright regions are enhanced and they correspond to the spectra of pure MO in its salt or base forms. 3.5. Conductivity The conductivity of globular and nanotubular PPy/silver composites has been measured on pellets prepared by compression of corresponding powders. The mechanical integrity of nanotubular PPy/silver pellets was better than those of globular PPy/silver composites. The globular PPy/silver composites prepared with silver nitrate alone could not be compressed to a pellet at all. The conductivity of PPy nanotubes prepared by the oxidation of pyrrole with iron(III) chloride hexahydrate in the presence of MO reported in the literature [34] is typically 11–68 S cm 1 and depended on the dimensions of nanotubes. In present study, we have used a mixture of oxidants (silver nitrate and iron(III) nitrate nonahydrate) at various mole ratios. It was expected that the highly conducting silver formed by the reduction of silver nitrate would increase the conductivity of composites. The high level of

dark regions

10

15

20

25

30

Fig. 9. Dependence of the conductivity, s , of nanotubular (full squares) and globular polypyrrole/silver composites (open squares) on volume fraction of the silver content, ’Ag, in the composites.

conductivity the PPy/silver composites in nanotubular form might be of benefit for potential application in biomedicine, such as in photothermal cancer therapy [50]. The conductivity of globular PPy/silver composites is lower compared with nanotubular form (Fig. 9) because globular PPy is less conducting than PPy nanotubes. It has been reported that the conductivity of PPy prepared in the presence of anionic surfactants is higher [11,51]. The molecule of MO used in the preparation of nanotubes comprises a large hydrophobic part as well as hydrophilic sulfonic group and it can, in principle, play a similar role as a surfactant to prepare PPy/silver nanotubes with improved conductivity (Fig. 9). The reason why surfactants may increase the conductivity of PPy has not been satisfactorily explained but it seems to positively affect the organization of PPy chains.

687 624

x=

865

1145 1048

925

Raman exc. 633 nm

1392 1319 1245

1588

Intensity

5

φAg, %

Fig. 7. Raman spectra of globular polypyrrole/silver composites with various composition of oxidant mixture, x.

Nanotubular

0

100 80 50

20 0

3000

2500

2000

1500

Wavenumbers cm

1000

500

–1

Fig. 8. Raman spectra of nanotubular polypyrrole/silver composites with various composition of oxidant mixture, x.

Fig. 10. Polypyrrole salt is deprotonated by ammonium hydroxide to corresponding polypyrrole base. Ammonium salt of an acid originally protonating polypyrrole is produced by neutralization.

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s B (S cm 1)

0 10 50 100

24 31 26 17

0.010 0.037 0.101 0.014

Raman exc. 633 nm 921

1609 1545 1395 1322 1242

bases

x=

875

s (S cm 1)

Intensity

x (mol%)

Nanotubular

1041

Table 1 The comparison of the conductivity, s , of nanotubular polypyrrole/silver composites prepared by the oxidation of pyrrole with iron(III) nitrate nonahydrate and silver nitrate mixed in various proportions, x, and of corresponding deprotonated forms, s B.

100-Base

50-Base

50 Base

2000

Wavenumbers, cm

2000

1500

Wavenumbers, cm

100 Base

3000

2500

1000

500

–1

770

1169

1028 903

1104

1600 1560 1640

3000

1535 1439

Absorbance

10 Base

1467 1358 1298

x=

4000

Nanotubular

FTIR in KBr

960

3437

10-Base

1000 –1

Fig. 11. FTIR spectra of deprotonated nanotubular polypyrrole/silver composites with various composition of oxidant mixture, x.

The conductivity should be discussed especially in terms of the silver content in the composites. For the composites of PPy/silver, the percolation of silver phase should result in the increase of conductivity. The weight fractions of silver, determined experimentally as an ash, have been recalculated to volume fractions by using densities of polypyrrole 1.3 g cm 3 and silver 10.5 g cm 3. No percolation threshold, however, has been observed for both composites with globular and nanotubular PPy, even though the fraction of silver was close to 30 vol.% (Fig. 9, globular PPy/silver composites). The decrease in conductivity with increasing content of silver for most of composites should be noted. For related polyaniline, it is known that the oxidants with lower oxidation potential yield products with higher content of non-conducting aniline oligomers compared with stronger oxidants [52]. This results in the reduction in the conductivity. In the present case, however, the oxidation potentials of iron(III) nitrate and silver nitrate are close, 0.77 and 0.80 V, respectively. The difference in acidity level of oxidant solutions may also cause the difference in the conductivity of product for a similar reason [53]. We can only speculate if the similar reasoning may apply also to PPy synthesis.

Fig. 12. Raman spectra of deprotonated nanotubular polypyrrole/silver composites with various composition of oxidant mixture, x.

the spectra of the as produced nanotubular PPy salts. The maxima of the bands are observed at 1560 (with a shoulder at 1600 cm 1), at 1467, 1358, 1298, 1169 (with a shoulder at 1104 cm 1), and at 1028, 903 and 770 cm 1. They are very close to each other for different composition of oxidant mixture and also to the spectrum of deprotonated nanotubular PPy prepared by oxidation with iron (III) chloride hexahydrate [49]. Raman spectra of nanotubular PPy bases differ from the spectra of the as produced nanotubular PPy salts (Fig. 12). The maxima of the bands are observed at 1609, 1545, 1395, 1322 (with a shoulder at 1242 cm 1) and at 1041, and 921 cm 1 (with a shoulder at 875 cm 1). As in case of the infrared spectra they are very close to each other for different composition of oxidant mixture and also to the spectrum of deprotonated nanotubular PPy prepared by oxidation with iron(III) chloride hexahydrate [49]. In optical images of the nanotubular PPy/silver composites we have also observed some red crystals. Their Raman spectra correspond to MO in salt form. 4. Conclusions The oxidations of pyrrole carried out in the absence and in the presence of methyl orange yield globular and nanotubular polypyrrole, respectively. This applies to both iron(III) nitrate and silver nitrate oxidants. Infrared spectra confirm that the molecular structure of polypyrrole is close for both oxidants. The oxidation with silver nitrate results in polypyrrole composites with silver particles. By varying the proportion between both oxidants, the content of silver in the composites was varied. The silver contents up to 63 wt.% in polypyrrole nanotubes and 78 wt.% for globules have not increased the overall conductivity of polypyrrole alone, and even a certain decrease was found. The conductivity of composites with nanotubular polypyrrole was higher, 10–30 S cm 1, compared with globular forms, 0.1–0.7 S cm 1.

3.6. Deprotonated samples (bases) Acknowledgements It has been observed for polyaniline/silver composites that the conversion of conducting polyaniline salt to non-conducting base surprisingly led to the increase of overall conductivity of composites [47]. For that reason, several of PPy/silver composites were deprotonated with ammonia (Fig. 10) and their conductivity determined. In the contrast to polyaniline, the conductivity of composites was reduced (Table 1). The molecular structure of the deprotonated nanotubular PPy/silver composites is not influenced by the presence of anions (Fig. 11). The infrared spectra of nanotubular PPy bases differ from

The authors thank the Czech Science Foundation (13-00270S) for financial support and to Dr. M. Cieslar from Charles University in Prague for providing TEM images. References [1] A.G. MacDiarmid, Angew. Chem. Int. Ed. 40 (2001) 2581–2590. [2] J. Stejskal, I. Sapurina, M. Trchová, Prog. Polym. Sci. 35 (2010) 1420–1481. [3] K. Lee, S. Cho, S.H. Park, A.J. Heeger, C.W. Lee, S.H. Lee, Nature 441 (2006) 65–68.

E. Alekseeva et al. / Synthetic Metals 209 (2015) 105–111 [4] H. Yamato, M. Ohwa, W. Wernet, J. Electroanal. Chem. 397 (1995) 163–170. [5] A. Boyle, E.M. Geniès, M. Lapkowski, Synth. Met. 28 (1989) 769–774. [6] A. Chaubey, K.K. Pande, V.S. Singh, B.D. Malhotra, Anal. Chim. Acta 407 (2002) 97–103. [7] T. Liu, L. Finn, M. Yu, H. Wang, T. Zhai, X. Lu, Y. Tong, Y. Li, Nano Lett. 14 (2014) 2522–2527. [8] P.A. van Hal, M.P.T. Christiaans, M.M. Wienk, J.M. Kroon, R.A.J. Janssen, J. Phys. Chem. B 103 (1999) 4352–4359. [9] M. Ferreira, V. Zucolotto, F. Huguenin, R.M. Torresi, O.N. Oliveira, J. Nanosci. Nanotech. 2 (2002) 29–32. [10] J.L. Wilson, P. Poddar, N.A. Frey, H. Srikanth, K. Mohomed, J.P. Harmon, J. Appl. Phys. 95 (2004) 1439–1443. [11] M. Omastová, M. Trchová, J. Kovárová, J. Stejskal, Synth. Met. 138 (2003) 447– 455. [12] N.K. Guimard, N. Gomez, C.E. Schmidt, Prog. Polym. Sci. 32 (2007) 876–921. [13] A.N. Zelikin, D.M. Lynn, J. Farhadi, I. Martin, V. Shastri, R. Langer, Angew. Chem. Int. Ed. 41 (2002) 141–144. [14] X.P. Jiang, Y. Marois, A. Traoré, D. Tessier, L.H. Dao, R. Guidoin, Z. Zhang, Tissue Eng. 8 (2002) 635–647. [15] D.D. Ateh, H.A. Navsaria, P. Vadgama, J. R. Soc. Interface 3 (2006) 741–752. [16] J. Fournier, G. Boiteux, G. Seytre, G. Marichy, Synth. Met. 84 (1997) 839–840. [17] L.X. Wang, X.G. Li, Y.L. Yang, React. Funct. Polym. 47 (2001) 125–139. [18] Z.L. Mo, Y.X. Sun, H. Chen, Eur. Polym. J. 43 (2007) 300–306. [19] M. Joulazadeh, A.H. Navarchian, Synth. Met. 199 (2015) 37–44. [20] N.V. Blinova, J. Stejskal, M. Trchová, J. Prokeš, M. Omastová, Eur. Polym. J. 43 (2007) 2331–2341. [21] F.J. Liu, Q.Y. Yuan, S.M. Shang, X.H. Yu, Q. Zhang, S.X. Jiang, Y.G. Wu, Compos. B Eng. 69 (2015) 232–237. [22] J.Y. Liu, J.J. Wang, X.H. Yu, L. Li, S.M. Shang, Micro Nano Lett. 10 (2015) 50–53. lu, Polym. Bull. 33 (1994) 535–540. [23] A.S. Saraç, C. Erbil, B. Ustamehmetog [24] M. Omastová, M. Mi9cušík, Chem. Pap. 66 (2012) 392–414. [25] S.B. Wang, G.Q. Shi, Mater. Chem. Phys. 102 (2007) 255–259. [26] Z.Q. Shi, Synth. Met. 160 (2010) 2121–2127. [27] K.H. Kate, K. Singh, P.H. Khana, Synth. React. Inorg. Metal-Org. Nano-Metal Chem. 41 (2011) 199–202. [28] Y.J. Jung, P. Govindaiah, S.W. Choi, I.W. Cheong, J.H. Kim, Synth. Met. 16 (2011) 1991–1995. [29] X.M. Feng, Chin. J. Chem. 28 (2010) 1359–1367.

111

[30] X.M. Yang, L. Liang, F. Yan, Chem. Lett. 39 (2010) 118–119. [31] D. Munoz-Rojas, J. Oró-Solé, O. Ayyad, P. Gómez-Romero, J. Mater. Chem. 21 (2011) 2078–2086.  ata, M. Varga, J. Prokeš, M. Cieslar, P. Bober, J. [32] J. Škodová, D. Kopecký, M. Vrn Stejskal, Polym. Chem. 4 (2013) 3610–3616. [33] J. Stejskal, Chem. Pap. 67 (2013) 814–848.  ata, P. Fitl, J. Stejskal, M. Trchová, P. Bober, Z. [34] J. Kopecká, D. Kopecký, M. Vrn Morávková, J. Prokeš, I. Sapurina, RSC Adv. 4 (2014) 1158–1551. [35] R. Ansari, A.F. Delavar, J. Iran. Chem. Soc. 5 (2008) 657–668. [36] F.M. Kelly, J.H. Johnston, T. Borrmann, M.J. Richardson, Eur. J. Inorg. Chem. 2007 (2007) 5571–5577. [37] M. Choi, J. Jang, J. Colloid Interface Sci. 325 (2008) 287–289. [38] X.M. Yang, Z.X. Zhu, T.Y. Dai, Y. Lu, Macromol. Rapid Commun. 26 (2005) 1736–1740. [39] X.M. Feng, H.P. Huang, J.J. Zhu, Nanotechnology 18 (2007) 195603. [40] X.M. Yang, L.A. Li, F. Yan, Sens. Actuators B: Chem. 145 (2010) 495–500. [41] X.M. Yang, L.A. Li, Synth. Met. 160 (2010) 1365–1367. [42] J.L.S. Antonio, L.M. Lira, V.R. Gonçales, S.I. Cordoba de Torresi, Electrochim. Acta 101 (2013) 216–224. [43] M. Li, W.G. Li, J. Liu, J.S. Yao, J. Mater. Sci. Mater. Electron. 24 (2013) 906–910. [44] J. Upadhyay, A. Kumar, Mater. Sci. Eng. B 178 (2013) 982–989. [45] S.B. Ye, J.C. Feng, ACS Appl. Mater. Interface 6 (2014) 9671–9679. [46] P. Bober, J. Liu, K.S. Mikkonen, P. Ihalainen, M. Pesonen, C. Plumed-Ferrer, A. von Wright, T. Lindfors, C. Xu, R.-M. Latonen, Biomacromolecules 15 (2014) 3655–3663. [47] P. Bober, J. Stejskal, M. Trchová, J. Prokeš, Polymer 52 (2011) 5947–5952.  á9 [48] M. Omastová, K. Mosn cková, P. Fedorko, M. Trchová, J. Stejskal, Synth. Met. 166 (2013) 57–62.  [49] G. Ciri c-Marjanovi c, S. Mentus, I. Pašti, N. Gavrilov, J. Krsti c, J. Travas-Sejdic, L.T. Strover, J. Kopecká, Z. Morávková, M. Trchová, J. Stejskal, J. Phys. Chem. C 118 (2014) 14770–14784. [50] K. Yang, H. Xu, L. Cheng, C.Y. Sun, J. Wang, Z. Liu, Adv. Mater. 24 (2012) 5586–5592. [51] M. Omastová, M. Trchová, J. Kovárová, J. Stejskal, Synth. Met. 143 (2004) 153–161. [52] I.Yu. Sapurina, J. Stejskal, Russ. J. Gen. Chem. 82 (2012) 265–275. [53] I.Yu. Sapurina, J. Stejskal, Russ. Chem. Rev. 79 (2010) 1123–1143.