synthesis and characterization of poly (indene-co-pyrrole) nanofibers

Received: 21 March 2009, Accepted: 22 June 2009, Published online in Wiley Online Library: 11 August 2009

Synthesis and characterization of poly(indene-co-pyrrole) nanofibersy

Shubhra Goela*, Nasreen A. Mazumdara and Alka Guptab

Nanofibers of poly (indene-co-pyrrole) (CInPy) have been synthesized, using a facile chemical oxidative polymeri-zation reaction. The effect of copolymerization was examined in view of the individually synthesized homopolymernanostructures of polyindene (PIn) and polypyrrole (PPy). Morphological details of CInPy, studied using scanningelectronmicroscopy (SEM) and transmission electronmicroscopy, (TEM) reveal the appearance of dense cottonymess,comprising of fine fibers with an average diameter of 5–10nm. Chemical structural analysis of CInPy, conducted usingultraviolet-visible (UV-Vis), Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR) spectroscopictechniques, reveals that both PIn and PPy are involved in the formation of copolymer organization. Fluorescenceproperties of nanosized copolymer are observed in the blue region, with emission lmax placed at 395nm. Conductivityof copolymer nanofibers (2.4T 10S3 S/cm) is consistent with the morphology and thermal stability properties ofintegral homo-polymers. Improved thermal stability and processability along with the enhanced optical and electricalproperties of copolymer nanostructures outfit it as a better promising material in optoelectronic and light emittingnanodevices, with reference to nanosized PIn and PPy. Copyright � 2009 John Wiley & Sons, Ltd.

Keywords: copolymer nanofibers; polyindene; polypyrrole; optical properties; thermal properties

INTRODUCTION

The science of nanostructured polymers has been quiteinnovative since the last decade due to the unique optical andelectrical properties exhibited by nanoscaled systems, superior tothose of corresponding bulk ones.[1–3] As a result of quantumconfinement,[4] their unusual properties pave way for potentialapplications in a variety of arenas including optoelectronics,luminescence materials, sensors, etc.[4–6] Studies have primarilybeen focused upon electrically conductive polymers. Suchnanostructures have proven to be highly intrigued chemicalsystems with novel physicochemical properties and proposedtechnological applications.[4–7] Attempts are also being made tofurther modify their properties by integrating them with othermolecular systems, either through composite or copolymerformation.[8–10] The formations of such blended nanostructures,whether copolymers or composites from different (two or more)monomers, are likely to bring up systems with characteristicfeatures, better or intermediary to the individual homopoly-mers.[11–13] However, it is always desired to investigate a newpolymeric unit and copolymer nanostructured system thatexhibit interesting properties, which have not been, possibly,much explored earlier.Polyindene (PIn) is a familiar polycyclic polymeric hydrocarbon,

which is obtained by the polymerization of indene under acidicconditions[14–15] and shows special optical properties.[15] How-ever, a major problem with PIn is its extreme brittle nature as aresult of its stiff backbone.[15] Moreover, this restrained structureof PIn due to inclusion of cyclopentane ring system,[16] restrictsthe movement of its polymeric chain and renders it a high glasstransition temperature. This makes PIn an insulating polymer andlimits its applications. One possibility of overcoming this drawbackmay possibly be its synthesis coupled with some suitablecompound that could retain and also enhance its inherentproperties in a better way.

On the other hand, polypyrrole (PPy) is an intrinsic conductingpolymer that serves potential applications in multidisciplinaryfields like batteries, chemical sensors, light emitting diodes,electrodes, actuators, etc.[17–19] Its easy synthesis, high conduc-tivity, and good environmental stability properties have out-shined it as a promising conductive polymer in recent years.[18–19]

At nanodimensional level also, PPy has been extensively exploredas nanowires, nanofilms, nanofibers, nanotubes, and other formsfor its possible technological applications.[20–22] However, thep–electron system along the PPy backbone generates rigidity,and the cross linking points between its polymeric chain make itinsoluble, infusible, and, therefore, poorly processable.[23]

Secondly, PPy shows low mechanical strength, that altogetherconfines its practical applications in many areas.[13]

It is now identified that union of PPy with other organicpolymers as copolymers and composites is associated withpromising synergic effects,[24] like improvements in mechanical

(wileyonlinelibrary.com) DOI: 10.1002/pat.1516

Research Article

* Correspondence to: S. Goel, Department of Chemistry, Jamia Millia Islamia(Central University), New Delhi-110025, India.E-mail: [email protected]

a S. Goel, N. A. Mazumdar

Department of Chemistry, Jamia Millia Islamia (Central University), New

Delhi-110025, India

b A. Gupta

Department of Chemistry, Dyal Singh College, Delhi University, Lodhi Road,

New Delhi-110003, India

y In the present work, we report the synthesis of one-dimensional poly (inde-ne-co-pyrrole) nanofibers, using a facile chemical oxidative polymerizationreaction. The effect of copolymerization has been examined, in view of theindividually synthesized homopolymer nanostructures of polyindene andpolypyrrole. Such study has not, so far, been reported in the literature. Theresearch work is novel and has not been published or produced in any journalin any form till now.

Polym. Adv. Technol. 2010, 21 888–895 Copyright � 2009 John Wiley & Sons, Ltd.

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properties[13] and processing.[25] Bozkurt et al.[13] have blendedPIn with PPy in the form of composite, that exhibits bettermechanical strength and thermal stability as compared tothe individual homopolymers. Copolymer nanostructures ofpyrrole with other conjugated p-bonds containing monomerslike aniline[26] and thiophene[12] have also been developed. Themain driving force behind these efforts is, the selection of novelmonomers that can be copolymerized with pyrrole and formstructures with improved optical, thermal, conductive, mechan-ical, and processability properties. Hence, it seems worthwhile toexplore the possibility of synthesizing and characterizing acopolymer system of ‘‘indene and pyrrole’’ at nanoscale, that mayexhibit interesting and improved properties compared to itsconstituent homopolymers. To the best of our knowledge, nosuch attempts have been made to synthesize and characterize acopolymer-based nanostructured system of these monomers.In the present work, we report the synthesis of poly

(indene-co-pyrrole) (CInPy) nanofibers, using a facile chemicaloxidative polymerization method. A major consideration focusedupon developing the copolymer nanostructures is, the improve-ment in the physical and optical properties of correspondinghomopolymeric nanomaterials (PIn and PPy).

EXPERIMENTAL

Materials used

All the chemicals were purchased from Sigma Aldrich. Indene(98%) and pyrrole (98%) were distilled under reduced pressure,prior to the initiation of reaction. All other chemicals (conc.sulphuric acid, methanol and dry ether) were used as received.

Synthesis method

Nanostructures of PIn, PPy, and CInPy were synthesized, using achemical oxidative polymerization method, based on a cationicpolymerization reaction of indene.[14] The synthesis of PIn andPPy nanostructures was carried out as follows: for PInnanomaterial, 7ml of conc. sulphuric acid was added slowly tofreshly distilled indene (0.05moles� 5ml), with fast magneticstirring in inert atmosphere. A reddish brown sticky product,formed within a span of few minutes, was collected andthoroughly washed with deionized water. It was further washedwith acetone, followed by deoxygenated methanol. On triturat-ing with ether, fine brown powder was obtained. Pyrrole waspolymerized in a similar manner as used for indene. For thesynthesis of CInPy nanostructures, 10ml of sulphuric acid wasadded dropwise under fast magnetic stirring to an equimolar(0.05moles of each:�5ml indene, and 3.47ml pyrrole) mixture ofindene and pyrrole in an inert gas atmosphere. The formedpolymerized product was collected, washed, and processed in amanner identical to that used for homopolymers, PIn and PPy.The procured samples were dried and kept in the vacuumdesiccator for subsequent analysis.

Characterization

The elemental details were obtained using Elementar Analysen-systeme, GmbH Vario EL composition detecting instrument.Scanning electron microscopic (SEM) images were obtained byLEO 435VP, a variable pressure scanning electron microscope. A

Phillips Morgani 268 microscope was used to collect thetransmission electron microscopic (TEM) images at a magnifi-cation of 14,000X and an exposure time of 100ms. Ultravio-let-visible (UV-Vis) spectra were recorded in CHCl3 solution, usingphoenix-2200DPCV UV-visible spectrophotometer. Fourier trans-form infrared (FTIR) spectra were recorded in transmission modein the mid IR range, using Perkin Elmer (Spectrum BX-II)spectrophotometer. Nuclear magnetic resonance (NMR) spectrawere recorded on a AV 300 spectrometer at 300MHz in CDCl3solution, maintaining the temperature at 258C. Thermal gravi-metric analysis (TGA) was performed, using Perkin ElmerDiamond thermal analyzer, by heating at a rate of 108C/min inair, in the temperature range 50–5008C. Fluorescence spectrawere obtained, using Perkin Elmer spectrophotometer, by meansof pellets having 10mm diameter and 1mm thickness. The DCconductivity measurements were evaluated at room temperatureby the standard 4 -Probe van der Pauw method.

RESULTS AND DISCUSSION

Mechanism

The proposed mechanism for the synthesis of PIn, PPy, and CInPynanostructures is shown in Scheme 1. For PIn (Scheme 1A), itfollows that: indene undergoes an electrophilic polymerization inacidic medium and generates persistent dimer carbocation,leading to the model PIn chain of polyindanyl cations. Thechemistry that occurs between the cationic chain and Lewis acid(H2SO4) results in the adhering of the HSO4

� into the model chainat a localized polaron site.[27] The single terminal indanyl cation,responsible for developing the PIn chain, propagates in a planarfashion in the available short span of polymerization time. For PPy(Scheme 1B), the mechanism follows that: on adding the acid tothe monomer, each neutral pyrrole molecule gets oxidized andyields its free cation radical species. These, then, combine with itsconsecutive radical species and form a dimer, then a trimer, andfinally result in a chain of positively charged PPy unit,[28] with thenegative charged counter anionic species HSO4

� attached at thepositive site of the PPy backbone.[29]

In case of CInPy (Scheme 1C), the pathway follows that: indeneand pyrrole, altogether, undergo an oxidative polymerizationreaction in the presence of the oxidizing agent, sulphuric acid.The pyrrole monomer adheres to the 2,3- position of the indeneunit and doping takes place at the site of pyrrole component,which, thereby, propagates the poly (indene-co-pyrrole) chainfurther.The formation of PIn, PPy, and CInPy is supported by the UV-Vis,

FTIR, and NMR studies discussed further.

Elemental analysis

The C, H, N, S, and O content in PIn, PPy, and CInPy nanostructuresis summarized in Table 1. Presence of N element in the CInPynanofibers proves the formation of a copolymer matrix. Besides,as almost half the percentage of the total C element in PIn andPPy (56.75%) nanostructures subsists in the CInPy (53.59%) andthe content of S element in PPy coincides with that of CInPy, itmay be inferred that pyrrole is the major component of thesynthesized copolymer matrix. The fact is further supported bythe existence of nearly halved percentage of N element in theCInPy to that present in PPy.

Polym. Adv. Technol. 2010, 21 888–895 Copyright � 2009 John Wiley & Sons, Ltd. View this article online at wileyonlinelibrary.com

SYNTHESIS AND CHARACTERIZATION OF NANOFIBERS

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Morphological analysis

The effect of individual molecular structure on the nanostruc-tured morphology is well explicit in the SEM images of PIn, PPy,and CInPy as shown in Fig. 1A-C respectively. As observed in themicrograph for PIn (Fig. 1A), the formation of isolated 1D thickfibers with average diameter of �10–15microns is indicated.

Whilst for PPy (Fig. 1B), a highly porous and random association ofnanofibers in a cauliflower type arrangement is signified,indicating the initial 1D growing model of PPy in high oxidizingenvironment.[30] In contrast, the CInPy (Fig. 1C) appears, more orless, like a bunch of coiled tendrils having smooth surface anduniform diameter between 100–200 nm. A dense parallelarrangement of such tendril like structures is also observed in

Scheme 1. Proposed mechanism pathway for the formation of PIn (A), PPy (B), and CInPy (C).

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S. GOEL, N. A. MAZUMDAR AND A. GUPTA

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the figure. It is important to note that the density ofnanostructures is greatly increased in the CInPy matrix, thanthat observed initially in PIn form.When observed under TEM, this divergence in morphology is

more clearly highlighted. The TEM images shown in Fig. 2 A-Cexplicitly highlight the characteristic morphological features ofPIn, PPy, and CInPy, respectively. The TEM image of PIn (Fig. 2A)depicts long fibers (lengths upto several microns) having smoothsurface and uniform diameter of �100–200 nm. For PPy (Fig. 2B),the dense pack of nanofibers observed in SEM image appears tobe composed of 1D, thin, and elongated tubular structures withan average diameter of �100 nm. These structures arenon-uniform and emerge out as rough surfaces. Interestingly,the CInPy (Fig. 2C) shows a dense cottony mesh type

arrangement, comprising of entangled thread-like fine fiberswith an average diameter of 5–10 nm. Formation of suchnanofibers with diameters of order 5 nm in a simple template freeapproach has been rare if not scarce.The key reasons for the differences in morphology of these

polymers may be attributed to (a) the variations in growth patternand (b) degree of polymerization, which altogether govern themorphological changes.[30] Presence of more active sites (inhighly oxidized environment) on the PPy chain causes itspolymerization to proceed in different directions, producingcauliflower-like structures.[30] However, in case of PIn, the singleterminal indanyl cation, responsible for developing the PIn chain(see Scheme 1A), propagates in a planar fashion in the availableshort span of polymerization time, causing the model chain tobreed in only one uniform direction with no side branchreactions. Nevertheless, in CInPy, a collective interaction ofindene and pyrrole monomers forming poly (indene-co-pyrrole)takes place, and as such, the intrinsic morphologies of both theindividual polymeric systems (PIn and PPy) result in a bunch ofcoiled, tubular 1D structures (SEM of CInPy, Fig. 1C) and, thus, thedensity is enhanced. Regularity in the PPy backbone is boosteddue to the prevention of sideway pyrrole–pyrrole polymerizationreactions, thereby decreasing its structural defects and formingordered and integrated structures.

Ultraviolet-visible spectroscopy

The UV-Vis absorption spectra of PIn (curve a) and CInPy (curve b)nanosized structures are overlaid in Fig. 3. The spectrum of PPy

Table 1. C, H, N, S, and O content in PIn, PPy, and CInPynanostructures

Element(%)

Polyindene(PIn)

Polypyrrole(PPy)

Copolymer(CInPy)

C 72.660 40.850 53.590H 5.960 5.915 5.787N 0.000 10.160 5.100S 3.217 10.590 10.520O 18.163 32.485 25.003

Figure 1. Scanning electron micrographs of PIn (A), PPy (B), and CInPy (C) nanostructures.



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nanomaterial could not be compared due to insolubility of thesample in the CHCl3 solution. The spectrum of PIn nanofibers(curve a) shows the characteristic sharp p–p� absorption peak at267 nm, typical to indene.[31] Compared to the optical spectra ofPIn, this absorption peak appears to be broader and slightlyshifted to lower wavelength at 262 nm in CInPy (curve b). Thechanged p-bond chromophore of indene–pyrrole aromatic ring

system in CInPy nanomaterial due to overlapping of phenylp-conjugated unit (of indene) and skeleton of pyrrole monomer,is possibly responsible for this blue shifted and broadenedabsorption peak. It is also observed that the weak shoulder in PInnear 320–330 nm, associated with indanyl and dimer cationformation in the growing PIn chain[14] and protonated state ofPIn,[14] extends till higher wavelength �400 nm in the CInPynanofibers. These additional absorptions suggest p–p� electrontransitions in the band gap of the conjugated pyrrole ringsystem,[21] existing in CInPy polymeric chain.Again, an added absorption band in the region of 476–533 nm

is observed in the optical spectra of CInPy nanofibers, which ischaracteristic to the bipolaronic absorption bands of dopedPPy.[32] The bands give evidence of p–p� electron transitions ofoxidized PPy[32] and indicate the formation of copolymer.Furthermore, formation of bipolarons in the copolymer matrixsuggests greater conjugated segments for CInPy than in the PInnanosized structures.[32]

Fourier transform infrared spectroscopy

The overlaid FTIR spectra of PIn (curve a), PPy (curve b), and CInPy(curve c) nanofibers in the mid-infrared range (500–3500 cm�1)are shown in Fig. 4. The FTIR spectrum of the mechanical mixtureof PIn and PPy nanomaterials (curve d) is also shown forcomparison.It has been observed that there is significant difference in the

FTIR spectra of PIn, PPy, and CInPy along with their respectivecharacteristics bands, revealing the formation of polymers and

Figure 2. Transmission electron micrographs of PIn (A), PPy (B), and CInPy (C) nanostructures.

Figure 3. UV-Vis spectra of PIn (a) and CInPy (b) nanofibers.



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co-polymer. In all these curves (curve a–c), the band at�600 cm�1 is observed. In PIn nanofibers (curve a), it isascribed to the out-of-plane bending of two CH groups of cisarrangement,[33] in PPy nanofibers (curve b), this band is assignedboth to the out-of-plane bending of two CH groups,[33] and theN�H out of plane vibration.[34] Interestingly, in CInPy nanofibers(curve c), this band is slightly more prominent, which may beattributed to the improvement in the molecular arrangement,indicating interactions of indene and pyrrole monomers. Thesharp band at�752 cm�1 in PIn spectrum is assigned to C�H ringout of plane bending vibrations[13] but in case of CInPy and themixture (curve d), it appears as a weak band. Besides this, thepeak attributed to the S¼O stretching[33] at 1060 cm�1 for PIn, isobserved at a lower wavenumber (at 1050 cm�1) for the PPynanosized fibers. However, this peak appears at a higherwavenumber, 1070 cm�1, for CInPy nanofibers. It is also notedthat in the PIn spectrum, a sharp peak at 1185 cm�1, overlappedwith the peak at 1205 cm�1 indicates the S¼O stretchingvibrations[35] thereby signifying the doped state of the polymer.However, doping in PPy is confirmed by the IR band at 1139 cm�1

overlapped by 1167 cm�1, as a consequence of influence of S¼Ostretching vibrations[36] on the C�H and N�H plane deformationbands. Moreover, the presence of doping in CInPy nanofibers isobserved at higher wavenumber of 1189 cm�1 overlapped by1217 cm�1, suggesting improved interaction of indene andpyrrole integral segments in the copolymer backbone. The IRband at �1445 cm�1, in the spectrum of PPy, is assigned to thecombination of C¼C stretching, C�N stretching, and deformationin pyrrole ring[26], and the band at �1470 cm�1 in the PInspectrum is assigned to C�C ring stretching frequency.[13] TheCInPy spectrum shows the presence of both these bands with aweaker intensity, revealing that the monomers (indene andpyrrole) are present in CInPy nanostructures.In addition, the PIn spectrum shows a peak at �3100 cm�1 in

the C¼C�H stretch[33] region, which disappears in the spectrumof CInPy. Moreover, the N�H stretch band at�3200 cm�1 (due tohydrogen bonded N�H groups)[33] in the spectrum of PPy andCInPy is expectedly absent in the spectrum of PIn. The above

results reveal that the monomers, indene and pyrrole, are wellincorporated in the CInPy nanostructures, and pyrrole ringsconstitute the dominant part of the copolymer formed (as alsosuggested in elemental studies).The chemical bonding between indene and pyrrole molecules

in the CInPy matrix is confirmed by comparing its IRcharacteristics with the FTIR spectrum of the mechanical mixtureof PIn and PPy nanomaterials. Significant differences can beobserved in the region 1100–1300 cm�1 (corresponding topyrrole ring vibrations modes)[36] and the band at �900 cm�1

(C�H bending vibrations),[36] which is present in CInPy but isabsent in spectrum of the mixture.The above FTIR studies reveal that all the IR bandmarkers in the

PIn and CInPy spectra are qualitatively much improved incomparison to those reported in literature,[13] showing wellresolved and sharp peaks due to the orderly arrangement ofmonomers in nanodimensions.

Nuclear magnetic resonance spectroscopy

1H NMR spectra of PIn and CInPy nanostructures are shown inFig. 5, which support their chemical organizations. The PPy

Figure 5. 1H NMR spectrum for the synthesized PIn (A) and CInPy

(B) nanofibers.

Figure 4. FTIR spectrum for nanofibrous structures of PIn (a), PPy

(b), and CInPy (c), and the mixture of PIn and PPy (d).



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nanomaterial was found to be insoluble in the CDCl3 medium,and hence its spectrum could not be recorded.The PIn nanofibers (Fig. 5A) show a multiplet in region

6.8–7.2 ppm, assigned to the aromatic protons.[15–16] Aliphaticprotons in PIn are located in the region 2.2–2.9 ppm, owing tocyclopentane ring current in the polymer.[15] The methyleneprotons are positioned at 1.2 as a sharp resonance singlet.[15]

Contrarily, the CInPy nanofibers (Fig. 5B) show a sharp singlet at7.2 ppm due to aromatic protons and the methylene protonsplaced at 1.7 ppm. In addition, a small peak is observed in theNMR spectrum of CInPy nanofibers at �4.2 ppm, which may beattributed to the N�H bond,[25] due to the incorporation ofpyrrole moiety. Furthermore, presence of N�H signals in CInPyindicates that N�H bond well resides in the copolymer chain andis in good agreement with the FTIR results, discussed earlier. Theabsence of aliphatic protons in CInPy, attributed to thecyclopentane ring current (present in indene monomer units),specifies the coupling of indene and pyrrole monomeric units at 2and 3 positions of indene ring and proves the polymerizationwith the pyrrole moiety at its site.

Thermal stability

The thermo-gravimetric (TG) scans of PPy (curve a), PIn (curveb), and CInPy (curve c) nanofibers are compared in Fig. 6,suggesting their degradation in three stages. In the first step,nearly 4–10% weight loss occurs in all nanostructures within thetemperature range of 100–1808C (�10% for PIn and�4% for PPyand CInPy), which is in general ascribed to the expulsion ofadhered water molecules, loss of dopant, and low molecularweight oligomers from the polymer matrixes.[29] The secondphase of thermal decomposition in these nanostructures isobserved in the 200–4008C range, which corresponds to thebreakdown of respective polymeric backbone chains.[29] Thepercentage of thermal degradation in this range (200–4008C) isalso observed to vary with the type of polymeric nanostructure. Itis highest for PIn (53%), followed by CInPy (38%), and then PPy(32%). Above 4008C, the nanosized polymers depict a constant

degradation pattern with rapid rise in temperature. During thefinal stage at 5008C, there is a total weight loss % of 86%, 55%,and 45% for PIn, CInPy, and PPy nanostructures, respectively.The above findings clearly indicate that the thermal stability for

these nanostructures follows the order, as PPy>CInPy>PIn. It isalso well observed that the overall TG-profile of CInPynanomaterial more resembles that of PPy nanomaterial ascompared to the PIn nanomaterial. The high weight loss % for PInis counteracted by the copolymerization of indene with pyrrole,thereby improving its thermal properties in the developedcopolymer nanofibers.

Fluorescence spectroscopy

In order to study the effect of copolymerization process on thefluorescent properties of the synthesized CInPy nanofibers withregard to nanosized PIn, fluorescent spectra of both polymerswere collected. Figure 7 shows the overlaid fluorescenceemission spectra for the synthesized PIn (curve a) and CInPy(curve b) nanostructures. It is observed from the spectra that,both PIn and CInPy nanostructures show fluorescent propertiesin the blue region with emission in the 360–470 nm (3.4–2.6 eV)region, and lmax is located at 430 and 395 nm, respectively.It may be marked that PIn nanofibers (curve a) show a red shift

due to the existence of increased number of phenyl rings in itsplanar structure that suppress the formation of p-aggregates andfence the quenching process.[37] However, the CInPy nanofibers(curve b) exhibit a comparative low energy excitation and higherpeak intensity in this region than the latter, suggesting moreordered structure and longer-conjugation length segments in itsmatrix.[38] This, in turn, supports the morphological and UV-Visspectra analysis discussed earlier.

Conductivity measurements

The electrical conductivity (EC) values for the PIn, PPy, and CInPynanostructures, measured at room temperature, are given inTable 2. From the data, it can be observed that the conductivityvalue of the CInPy nanofibers lies between that of integralcomponents (PIn and PPy), PPy displaying the highest EC value. It

Figure 6. Thermogravimetric curve for the nanodimensional structures

of PPy (a), PIn (b), and CInPy (c). Figure 7. Fluorescence spectra for PIn (a) and CInPy (b) nanostructures.



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is in good agreement with regard to the morphological andthermal characteristics of the respective polymers, as discussedearlier.It is noted that the charge created on the doped PIn backbone

(Scheme 1A), due to protonation in the form of polarons (radicalcations), is responsible for EC. High planarity in PIn structureleads to easier charge transport and explains the conductivity forit. However, the delocalization interrupted by chain-endsdecreases its conjugation length, and consequently, the EC ofthe polymer. Copolymerization of indene with pyrrole signifi-cantly increases the conductivity value in the resultingcopolymer nanofibers. This improvement in EC value of CInPynanostructures can be accounted due to the following mainreasons: (a) enhanced conjugation length[39] between thearomatic rings (indene and pyrrole) along the copolymer chainwhich led to easier charge flow; (b) presence of additionalbipolarons[32] attributed to oxidized pyrrole, incorporated in thecopolymer matrix; (c) better molecular order in the copolymerchains.[40]

CONCLUSIONS

The work contributes two exciting research areas: firstly, facilesynthesis of nanosized conducting polymer, and secondly, theformation of a novel nanostructured copolymer system, exhibit-ing unique functionality. Poly (indene-co-pyrrole) nanofiberssynthesized using a one-step chemical route display significantimproved properties in contrast to the integral homopolymers:PIn and PPy. Pyrrole seems to play an important role in thecopolymerization of indene, thereby gaining control over theconstrained structural features of the nanofabricatedmaterial in abetter way, leading to enhanced coplanar characteristics in thePIn backbone. Furthermore, the results indicate that thestructural defects in the rigid PPy backbone could be combatedon coupling indene with pyrrole, and in doing so, theprocessability (solubility) of PPy can be increased.The findings reveal that CInPy nanofibers enclose the proper-

ties well desired in the nanodimensioned PIn and PPy, andpropose them as a substitute material of conducting polymer fordifferent nanotechnological applications.

Acknowledgements

The authors express their gratitude to Jamia Millia Islamia andthe Principal of Dyal Singh College, for providing the researchfacilities.

REFERENCES

[1] E. Roduner, Chem. Soc. Rev. 2006, 35, 583.[2] S. Goel, A. Gupta, K. P. Singh, R. Mehrotra, H. C. Kandpal, Mater. Sci. &

Eng. A 2007, 443, 71.[3] D. R. Paul, L. M. Robeson, Polymer 2008, 49, 3187.[4] J. I. Pascual, J. Mendez, J. Gomez-Herrero, A. M. Baro, N. Garcia, U.

Landman, W. D. Luedtke, E. N. Bogachek, H-P. Cheng, Science 1995,267, 1793.

[5] L. Meng, Y. Lu, X. Wang, J. Zhang, Y. Duan, C. Li,Macromolecules 2007,40, 2981.

[6] J. A. Pomposo, E. Ochoteco, C. Pozo, P. M. Carrasco, H. J. Grande, F.Rodrı́guez, Polym. Adv. Technol. 2006, 17, 26.

[7] A. Gupta, S. Goel, K. P. Singh, R. Mehrotra, H. C. Kandpal, Indian J.Chem. A 2006, 45A, 1831.

[8] H. A. Patel, R. S. Somani, H. C. Bajaj, R. V. Jasra, Bull. Mater. Sci. 2006,29(2), 133.

[9] I. W. Hamley, Nanotechnology 2003, 14, R39.[10] D. Mecerreyes, R. Stevens, C. Nguyen, J. A. Pomposo, M. Bengoetxea,

H. Grande, Synth. Met. 2002, 126, 173.[11] B. Sari, M. Talu, Synth. Met. 1998, 94, 221.[12] X. Li, M. Lu, H. Li, J. Appl. Polym. Sci. 2002, 86, 2403.[13] A. Bozkurt, U. Akbulut, L. Toppare, Synth. Met. 1996, 82, 41.[14] M. Givehchi, A. Polton, M. Tardi, M. Moreau, P. Sigwalt, J. P. Vairon,

Macromol. Symp. 2000, 157, 77.[15] S. Kanaoka, N. Ikeda, A. Tanaka, H. Yamaoka, T. Higashimura, J. Polym.

Sci. A: Polym. Chem. 2002, 40, 2449.[16] S. F. Hahn, M. A. Hillmyer, Macromolecules 2003, 36, 71.[17] R. Ansari, E-J. Chem. 2006, 3(13), 186.[18] H. N. ME. Mahmud, A. Kassim, Z. Zainal, W. M. M. Yunus, J. Appl. Polym.

Sci. 2006, 100, 4107.[19] S. Xing, G. Zhao, J. Appl. Polym. Sci. 2007, 104, 1987.[20] W. Zhong, S. Liu, X. Chen, Y. Wang, W. Yang,Macromolecules 2006, 39,

3224.[21] U. Sree, Y. Yamamoto, B. Deore, H. Shiigi, T. Nagaoka, Synth. Met.

2002, 131, 161.[22] S. Goel, N. A. Mazumdar, A. Gupta, Polym. Adv. Technol. 2009, DOI:

10.1002/pat.1417[23] J. Rodriguez, H.–J. Grande, T. F. Otero, in Handbook of Organic

Conductive Molecules and Polymers: Conductive Polymers: Synthesisand Electrical Properties, (Ed. H. S. Nalwa), vol. 2, John Wiley & SonsLtd, New York, 1997, pp. 15–468.

[24] R. Turcu, D. Bica, L. Vekas, N. Aldea, D. Macovei, A. Nan, O. Pana, O.Marinica, R. Grecu, C. V. L. Pop, Rom. Rep. Phys. 2006, 58(3), 359.

[25] X. Li, L. Wang, Y. Jin, Z. Zhu, Y. Yang, J. Appl. Polym. Sci. 2001, 82, 510.[26] X. Li, X. Zhang, H. Li, J. Appl. Polym. Sci. 2001, 81, 3002.[27] C. Eristi, M. Yavuz, H. Yilmaz, B. Sari, H. I. Unal, J. Macromol. Sci. A: Pure

Appl. Chem. 2007, 44, 759.[28] J. Kim, D. Sohn, Y. Sung, E. Kim, Synth. Met. 2003, 132, 309.[29] M. Han, Y. Chu, D. Han, Y. Liu, J. Colloid Interface Sci. 2006, 296, 110.[30] S. Goel, A. Gupta, K. P. Singh, R. Mehrotra, H. C. Kandpal, Inter. J. Appl.

Chem. 2006, 2(3), 157.[31] A. L. Person, G. Eyglunent, V. Daele, A. Mellouki, Y. Mub, J. Photochem.

Photobiol. A: Chem. 2008, 195, 54.[32] R. Turcu, R. Grecu, M. Brie, I. Peter, A. Bot, W. Graupner, Studia

Universitatis Babes- Bolyai, Physica, special issue 2001, 216.[33] H. F. Shurvell, in Spectra-Structure Correlations in the Mid-and Far-

Infrared in Handbook of Vibrational Spectroscopy, (Eds. J. M. ChalmersP. F. Griffith), John Wiley & Sons Ltd, New York, vol. 3 2002,pp. 1783–1816.

[34] Y. Tian, F. Yang, W. Yang, Synth. Met. 2006, 156, 1052.[35] W. Prissanaroon, L. Ruangchuay, A. Sirivat, J. Schwan, Synth. Met.

2000, 114, 65.[36] M. Omastova, M. Trchova, J. Kovarova, J. Stejskal, Synth. Met. 2003,

138, 447.[37] D. H. Kim, J. A. Lee, S. U. Son, Y. K. Chung, C. H. Choi, Tetrahedron Lett.

2005, 46, 4627.[38] C. A. Breen, T. Deng, T. Breiner, E. L. Thomas, T. M. Sager, J. Am. Soc.

2003, 125(33), 9942.[39] P. M. Carrasco, H. J. Grande, M. Cortazar, J. M. Alberdi, J. Areizaga, J. A.

Pomposo, Synth. Met. 2006, 156, 420.[40] W. Chen, X. Wan, N. Xu, G. Xue, Macromolecules 2003, 36, 276.

Table 2. EC values for the synthesized PIn, PPy, and CInPynanofibers

Polymer Conductivity s (S/cm1)

PIn 1.73� 10�4

PPy 6� 10�2

CInPy 2.4� 10�3



895

synthesis and characterization of poly (indene-co-pyrrole) nanofibers

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