J O U R N A L O F C H E M I S T R Y Materials Electrically conductive graft copolymers of poly(methyl methacrylate) with varying polypyrrole and poly(3-alkylpyrroles) contents Siu-Choon Ng,a* Hardy S. O. Chana,b Jun-Feng Xiaa and Wanglin Yua aDepartment of Chemistry, National University of Singapore, Kent Ridge Crescent, Singapore 119260 bDepartment of Materials Science, National University of Singapore, Kent Ridge Crescent, Singapore 119260 Received 27th April 1998, Accepted 14th August 1998 Pyrrole and 3-alkylpyrroles were grafted via chemical oxidative polymerisation with FeCl3 to copolymers of methyl methacrylate and v-(N-pyrrolyl )alkyl methacrylates incorporating varying amounts of v-(N-pyrrolyl )alkyl methacrylates with varying alkyl chain lengths.The electrical conductivity of the resultant graft copolymers attained 10-4–10-3 S cm-1, with the length of the alkyl spacers in v-(N-pyrrolyl )alkyl methacrylates having little influence on the conductivity.A longer alkyl spacer, however, resulted in a lower glass transition temperature for the resulting graft copolymers. The graft copolymers from pyrrole were insoluble whilst those arising from 3-alkylpyrroles were completely soluble in common organic solvents even in their doped states.The past two and a half decades have witnessed intense Experimental interdisciplinary research attention on electrically conducting Synthesis of key monomers conjugated polymers such as polyacetylenes, polyanilines, polypyrroles and polythiophenes on account of their remarkable Pyrrole (Py), methacryloyl chloride and methyl methacrylate electronic, magnetic and optical properties as well as their (MMA) were distilled prior to use.a,a¾-Azobis(isobutyropotential in a wide range of technological applications.1–6 nitrile) (AIBN) (Koch-Light) was recrystallized from absolute However, the generally poor processability of these parent ethanol and dried at 40 °C in vacuo (0.2 mmHg).unfunctionalised systems has severely limited their appli- Triethylamine, dimethyl sulfoxide (DMSO) and nitromethane cations. Consequently, much research has been devoted to were distilled over CaH2. Other chemicals were used as improving the processability of the conductive polymers.7–12 received. Amongst these approaches, the combination of conducting The key monomers of v-(N-pyrrolyl )-n-alkyl methacrylate polymers, particularly polypyrroles, with conventional poly- (NPAM) were synthesized as shown in Scheme 1.mers has been the recent focus of several research groups. Tetrahydropyran (THP)-protected v-bromoalkanols used in Polypyrrole was first grafted onto polystyrene by electrochemi- this synthesis were prepared by bromination of a,v-diols13 cal polymerisation of pyrrole in the presence of a pyrrole followed by THP-protection of the terminal hydroxy groups.derivative of polystyrene.7 The graft copolymers had electrical 3-Alkylpyrroles (3APys) were synthesized according to literaconductivity of 0.05–5 S cm-1 depending on the pyrrole ture procedures14,15 except for the replacement of LiAlH4 for content.However, no information pertaining to the pro- NaAlH2(OCH2CH2OCH3)2 as the reducing agent. cessability of the graft copolymers was reported. Over the past several years, Stanke and co-workers have successfully grafted Polymerization polypyrrole to poly(methyl methacrylate) (PMMA) by The graft copolymers, poly[methyl methacrylate-co-v-(N-pyr- eVecting the chemical oxidative polymerisation of pyrrole in rolyl )alkyl methacrylate]s (PMMA-co-PNPAMs): PMMA-co- the presence of methyl methacrylate–2-(N-pyrrolyl )ethyl PNPHM, PMMA-co-PNPOM, PMMA-co-PNPDM, and methacrylate copolymer using FeCl3 as an oxidant.12 The film PMMA-co-PNPDDM corresponding to n-alkyl spacers of 6, conductivity of the graft copolymers attained a maximum of 8, 10 and 12 carbons, respectively, in NPAMs were obtained 2×10-2 S cm-1,12a,12c though only marginal solubility was by copolymerization of methyl methacrylate (MMA) with the achieved.12a Although soluble samples of the graft copolymers corresponding NPAMs in THF at 60 °C for 22 h using AIBN could be obtained at a very low polypyrrole content,12b no as an initiator.Thereafter, pyrrole and 3-alkylpyrrole moieties corresponding conductivity datum was reported.In addition, were grafted onto PMMA-co-PNPAMs by eVecting oxidative only an N-pyrrolylethyl spacer group on the pendant ester in polymerisation with 2.5 mole equivalents of anhydrous FeCl3 the precursor copolymer was studied. It is anticipated that in nitromethane at 0 °C for 6 h (Scheme 1). The resultant graft incorporation of longer alkyl spacers between pyrrole and the copolymers were precipitated by pouring into 5% HCl in PMMA backbone will have a significant impact on both the methanol at 0 °C.The precipitate was washed with methanol electrical conductivity and processability of the resultant graft until the solvent remained colorless (for the pyrrole grafted copolymers. Accordingly, with a view to investigating copolymers, the precipitate was stirred in THF overnight after structure–property relations, we have synthesized a series washing with methanol )12b,12e and dried under vacuum of graft copolymers of polypyrrole and poly(3-alkylpyrroles) (0.1 mmHg) at room temperature for 24 h.with the copolymers of methyl methacrylate (MMA) and v-(N-pyrrolyl )alkyl methacrylate of diVerent n-alkyl chain Measurements lengths.It was found that the attachment of long alkyl groups at the 3-position of pyrrole aVorded soluble, film-castable Elemental analyses from which the compositions of the graft copolymers in their doped states with electrical conduc- copolymers and the graft copolymers were calculated were performed at the National University of Singapore tivity in the semiconducting range.J. Mater. Chem., 1998, 8(11), 2347–2352 2347conducted from room temperature to 400 °C at a heating rate of 10 °Cmin-l with about 3 mg samples. Conductivity measurements were carried out on a four point probe connected to a Keithley constant-current source system. Gel permeation chromatographic analyses were carried out using a Waters 600E HPLC system with a Waters 410 diVerential refractometer.The molecular weights referred to the peak maxima of the elution curves were measured against polystyrene standards in THF at 30 °C using the following column combination: PhenogelTM MXL and MXM columns (300 mm×4.6 mm ID), with a separating range from 103 to 106 g mol-1. Results Precursor copolymers PMMA-co-PNPAMs The PMMA-co-PNPAM samples prepared in our experiments were soluble white powders with molecular weights (Mn) of ca. 50 000 g mol-1. Their chemical structures were confirmed by 1H NMR and FTIR spectroscopy. A representative 1H NMR spectrum for PMMA-co-PNPDDM containing 7.7 mol% of pyrrolyl moieties revealed resonances for the a-, b-ring protons at d 6.65 and 6.13 respectively.16a,16b The corresponding FT-IR spectra of the PMMA-co-PNPAMs depict characteristic vibrational bands at 1730 cm-1 (ascribable to ester carbonyl vibrations), 750 and 725 cm-1 ascribable respectively to pyrrole C–Hb and C–Ha bendings (Fig. 2a).12a,12c,12e TGA in air for PMMA-co-PNPAMs revealed an onset decomposition temperature at 180–240 °C, being completely degraded at ca. 450 °C leaving residues of <0.5%. Glass transition temperatures (Tg) of the copolymers were found to be lowered with increasing content of NPAMs.In addition, Tg at a given mole percentage of NPAM in the copolymer was also reduced with increasing length of the n-alkyl spacers in NPAMs (see Fig. 1) suggesting enhanced chain mobility of the copolymers with the longer spacers. Graft copolymers of PMMA with polypyrrole Black insoluble electrically conductive materials resulted from grafting of polypyrrole to PMMA-co-PNPAMs.However, those prepared from copolymers with a low content of NPAMs (<3 mol%) and of grafted polypyrrole (<20 mol%) showed some swelling in THF. Examination of the representative FTIR spectra (see Fig. 2) revealed that the absorption band at ca. 725 cm-1 attributed to C–Ha bending of the pyrrolyl Scheme 1 Reaction scheme for the syntheses of key monomers of v-(N-pyrrolyl )-n-alkyl methacrylate and graft copolymers with polypyrroles and poly(3-alkylpyrrole)s.Microanalytical Laboratory on a Perkin Elmer 240C elemental analyzer for C, H and N determinations. FT-IR spectra of polymers dispersed in KBr disks were recorded on a Bio-Rad TFS156 spectrometer. 1H NMR were recorded on a Bruker ACF 300 FT-NMR spectrophotometer operating at 300 MHz. CDCl3 was used as solvent and tetramethylsilane (TMS) as internal reference. Thermogravimetric analyses (TGAs) of polymer powders (about 5 mg) were conducted on a Du Pont Thermal Analyst 2100 system with a TGA 2950 thermogravimetric analyzer. A heating rate of 10 °Cmin-l with an air flow of 75 ml min-l was used, the runs being conducted from room temperature to 800 °C.DiVerential scanning calorimetry Fig. 1 Changes in Tg of the copolymers: (a) PMMA-co-PNPHM (2); (DSC) was conducted with a DSC 2910 module in conjunction (b) PMMA-co-PNPOM (&); (c) PMMA-co-PNPDM ($); (d) PMMA-co-PNPDDM (×). with the Du Pont Thermal Analyst system. The analyses were 2348 J. Mater. Chem., 1998, 8(11), 2347–2352Table 1 Shift in CNO stretching vibration of pyrroles grafted copolymers Contents of Py or nCNO/ Graft copolymersa 3APys/mol% cm-1 PMMA-co-PNPHM (6.7%) 20.4 1729 with pyrrole 28.9 1724 33.6 1721 PMMA-co-PNPDDM (1.6%) 12.7 1733 with pyrrole 33.1 1720 PMMA-co-PNPHM (2.6%) 12.4 1731 with 3-octylpyrrole 23.4 1731 31.1 1731 39.9 1729 aThe percentages in parentheses represent the content of NPAMs in PMMA-co-PNPAMs in mol%. moieties in PMMA-co-PNPAMs had disappeared subsequent to the grafting reaction due to the coupling of pyrrole rings.The intense absorption band due to the ester carbonyl functionality at 1730 cm-1 was observed to have shifted to lower wavenumber with increasing polypyrrole content (Table 1). This phenomenon could be ascribable to the formation of NH,ONC hydrogen bonding between the grafted polypyrrole and the ester groups of the PMMA copolymers.12c Table 2 summarises the electrical conductivity of the various polypyrrole grafted copolymers. The electrical conductivity Fig. 2 FTIR spectra of: (a) PMMA-co-PNPDDM with a NPDDM content of 4.2 mol% prior to grafting with pyrroles; (b) its polypyrrole grafted copolymer containing 28.2 mol% of pyrrole; (c) poly(3-octylpyrrole) grafted copolymer containing 21.4 mol% of 3-octylpyrrole.Fig. 4 Scanning electron microscopy (SEM) pictures of cast films of Fig. 3 1H NMR spectra of (a) copolymer of PMMA-co-PNPHM poly(3-alkylpyrrole) grafted onto PMMA-co-PNPHM containing 2.6 mol% of PNPHM: (a) poly(3-octylpyrrole) grafted copolymer containing 2.6 mol% of PNPHM and the poly(3-dodecylpyrrole) grafted copolymer containing 19.0 mol% of 3-dodecylpyrrole at (b) a containing 12.4 mol% of 3-octylpyrrole; (b) poly(3-decylpyrrole) grafted copolymer containing 24.7 mol% of 3-decylpyrrole. normal Relaxation Delay (RD) of 1 s; (c) when RD increased to 10 s. J.Mater. Chem., 1998, 8(11), 2347–2352 2349Table 2 Properties of polypyrrole grafter copolymers of PMMA Yield of Conductivitya/S cm-1 Copolymers Contents of NPAMs in Mn of PMMA- Feed ratio graft Contents of Py in (PMMA-co-PNPAMs) PMMA-co-PNPAMs/ co-PNPAMs/ CPNPAMs/ copolymers graft copolymers xpy/ Further used mol% g mol-1 Cpy (%) mol% Pristine doped with I2 PMMA-co-PNPHM 2.6 41400 1/10 43 26.7 — — 2.6 1/40 46 47.1 3.0×10-4 3.2×10-4 6.7 58600 1/5 57 20.4 — — 6.7 1/10 33 28.9 — 4.8×10-5 6.7 1/20 41 33.6 2.2×10-4 3.1×10-4 PMMA-co-PNPOM 0.2 44400 1/5 50 16.7 4.9×10-4 5.4×10-4 0.2 1/10 33 24.5 5.6×10-4 8.9×10-4 0.2 1/40 40 45.9 8.9×10-4 7.8×10-4 2.4 43300 1/10 46 18.4 — — 2.4 1/40 59 36.1 3.9×10-4 5.0×10-4 PMMA-co-PNPDM 0.9 49300 1/10 58 23.4 — — 0.9 1/20 47 26.3 3.4×10-4 3.2×10-4 0.9 1/40 43 44.2 6.0×10-4 7.7×10-4 3.6 47400 1/10 56 21.1 — — 3.6 1/20 58 27.6 — 1.8×10-5 3.6 1/40 38 30.4 5.5×10-4 8.3×10-4 PMMA-co-PNPDDM 1.6 41400 1/20 60 33.1 — — 1.6 1/40 38 44.7 6.5×10-3 7.8×10-3 4.2 52600 1/10 49 23.2 — — 4.2 1/40 52 29.7 1.2×10-4 5.8×10-4 a — means the conductivity is less than 1.0×10-5 S cm-1.was found to increase with increasing content of grafted chain have the eVect of reducing the chain mobility of the resultant graft copolymers to some degree which consequently polypyrrole attaining 10-4–10-3 S cm-1 when the pyrrole contents were less than 50 mol%.Higher contents of grafted results in higher Tg. polypyrrole did not result in any significant increase in the conductivity. In addition, further doping with iodine at room Graft copolymers of PMMA with poly(3-alkylpyrrole)s temperature did not result in any distinct rise in conductivity, indicating that the graft copolymers had already been fully The graft copolymers from 3-alkylpyrroles having octyl, decyl, and dodecyl pendants with PMMA-co-PNPAMs also aVorded doped in the grafting process. There were no obvious eVects arising from the use of diVerent alkyl spacers in NPAMs or black powders.Their key properties are summarised in Table 4.Their molecular weights (Mn) showed an apparently marginal of varying the content of NPAMs in PMMA-co-PNPAMs on the electrical conductivity of the resultant graft copolymers. increase in comparison to the precursor copolymers (PMMAco- PNPAMs). It was found that the graft copolymers prepared The Tg values of some polypyrrole-grafted copolymers are depicted in Table 3.On comparing Fig. 1 with Table 3, it is from PMMA-co-PNPAMs having low NPAM contents (<2.6 mol%) were completely soluble in common organic clearly evident that Tg of the polypyrrole-grafted copolymers are somewhat higher than the corresponding PMMA-co- solvents (THF, CHCl3, and acetone) even in their doped states irrespective of the grafted poly(3-alkylpyrrole) (P3APy) con- PNPAMs.In addition, Tg of the graft copolymers prepared from the same precursor copolymers PMMA-co-PNPAMs tent. Cast films of the P3APy grafted copolymers from their chloroform solutions on glass slides were examined using containing the same molar percentage of PNPAMs can be seen to increase with increasing grafted polypyrrole content. scanning electron microscopy (SEM) (see Fig. 4 for representative SEM pictures). At lower 3-alkylpyrrole contents, the graft This indicates that pyrrole units grafted onto the PMMA Table 3 Tg of polypyrrole grafter copolymers of PMMA Copolymers Contents of NPAMs in Mn of Contents of grafted Tg of graft (PMMA-co-PNPAMs) PMMA-co-PNPAMs/ PMMA-co-PNPAMs/ Py in copolymers xpy/ copolymers/ used mol% g mol-1 mol% °C PMMA-co-PNPHM 2.6 41400 0 124.1 2.6 26.7 130.0 6.7 58600 0 113.8 6.7 28.9 146.2 PMMA-co-PNPOM 2.4 43300 0 113.3 2.4 8.1 119.2 2.4 18.4 127.6 PMMA-co-PNPDM 0.9 49400 0 119.3 0.9 23.4 122.2 0.9 44.2 129.8 3.6 47400 0 110.0 3.6 13.1 113.5 3.6 27.6 124.9 PMMA-co-PNPDDM 1.6 41400 0 118.3 1.6 12.7 127.5 1.6 33.1 132.8 1.6 44.7 133.7 4.2 52600 0 95.3 4.2 16.4 122.8 2350 J.Mater.Chem., 1998, 8(11), 2347–2352Table 4 Properties of the poly(3-alkylpyrrole)s grafted copolymers of PMMA Content of Copolymers Yield of 3APy in (PMMA-co- Mn of PMMA-co- Feed ratio graft graft Mn of graft PNPAMs) PNPAMs/ CPNPAMs/ copolymers copolymers/ copolymers/ Conductivityb 3-Alkylpyrroles useda g mol-1 C3APy (%) mol% g mol-1 S cm-1 Solubilityc 3-Octylpyrrole PMMA-co- 41400 1/10 78 12.4 n.d.— + PNPHM (2.6%) 1/20 81 23.4 n.d. 4.8×10-4 + 1/30 89 31.1 42000 8.6×10-4 + PMMA-co-PNPOM 44400 1/10 88 12.4 n.d. — + (0.2%) 1/20 79 18.9 n.d. 8.8×10-5 + PMMA-co-PNPDM 49300 1/10 75 11.8 n.d. — + (0.9%) 1/20 80 25.5 50100 1.3×10-4 + PMMA-co-PNPDDM 41400 1/10 88 13.6 n.d. — + (1.6%) 1/20 90 20.2 n.d. 1.0×10-4 + PMMA-co-PNPDDM 52600 1/10 90 13.9 — — ± (4.2) 1/20 88 21.4 — 2.3×10-4 ± PMMA-co-PNPDDM 49800 1/10 89 19.4 — — – (7.7%) 1/20 86 24.0 — 1.2×10-4 – 3-Decylpyrrole PMMA-co- 41400 1/20 78 24.7 42300 3.0×10-4 + PNPHM (2.6%) PMMA-co-PNPOM 44400 1/20 81 21.4 n.d. 1.3×10-4 + (0.2%) PMMA-co-PNPDM 49300 1/20 79 18.3 n.d. 1.2×10-4 + (0.9%) PMMA-co-PNPDDM 41400 1/20 86 20.2 42100 2.3×10-4 + (1.6%) 3-Dodecylpyrrole PMMA-co- 41400 1/20 87 19.0 n.d. 2.5×10-4 + PNPHM (2.6%) PMMA-co-PNPOM 44400 1/20 84 19.4 44800 8.0×10-4 + (0.2%) PMMA-co-PNPDM 49300 1/20 85 20.2 n.d. 2.5×10-4 + (0.9%) PMMA-co-PNPDDM 41400 1/20 90 19.5 42100 3.9×10-4 + (1.6%) aThe percentages in parentheses represent the content of NPAMs in PMMA-co-PNPAMs in mol%. b — means the conductivity is less than 1.0×10-5 S cm-1. cRefers to solubility in CHCl3, THF, and acetone: ‘+’ completely soluble; ‘±’ partially soluble; ‘–’ insoluble.n.d. means not determined. copolymers appeared homogeneous suggesting the grafted prohibit crosslinking between pyrrole rings may also be the cause of the great improvement in the solubility of 3APy P3APy to have completely dissolved into the PMMA-co- PNPAM copolymers (Fig. 4a). However, at higher P3APy grafted copolymers.With increasing contents of NPAMs in PMMA-co-PNPAMs, the solubility of the resultant graft contents, the graft copolymers displayed a globular network structure (Fig. 4b) which could be attributed to phase copolymers decreased. Thus, the graft copolymers of 3-octylpyrrole with PMMA-co-PNPDDMs were completely soluble, separation/aggregation of the P3APy component in the graft copolymers.This observation is suggestive that at lower 3- partially soluble and insoluble when the content of NPDDM in PMMA-co-PNPDDMs was increased from 1.6 to 4.2 and alkylpyrrole contents, homogeneous grafted copolymers resulted whereas at higher contents, an apparently then 7.7 mol%, respectively (Table 4). This could be attributed to the crosslinking between NPAM units, which is more likely incompatible polymer blend between two polymers resulted.As with polypyrrole grafted copolymers the FTIR spectra with increasing content of NPAMs in PMMA-co-PNPDDMs. As with the polypyrrole grafted copolymers, the conductivity of P3APy (Fig. 2c) grafted materials revealed the disappearance of the C–Ha bending vibrational band indicative of a of the P3APy grafted copolymers increases with the content of P3APys attaining ca. 10-4 S cm-1 at about 20 mol%. successful grafting process via a–a couplings of P3Apy to the pyrrolyl moieties in PMMA-co-PNPAMs. Further corrobor- Thereafter, further increase in the content of 3APys did not result in any further increase of the conductivity of the ation for this was provided from the disappearance of the aproton signal in the 1H NMR spectra of the representative resultant graft copolymers as evident in Table 4 from the representative experimental results based on the graft copoly- poly(3-dodecylpyrrole) grafted copolymers (Fig. 3). However, the signal at ca. 6.15 ppm due to the b-protons of the pyrrolyl mer of 3-octylpyrrole and PMMA-co-PNPHM (containing 2.6 mol% NPHM). Further, from Table 2 and 4, the introduc- moiety also disappeared.This phenomenon was also previously observed by Stanke et al.12b,16b and was attributed to the tion of long alkyl groups onto the 3-position has only marginal influence on the conductivity of the resultant graft copolymers. formation of aggregates and slow relaxation of the said resonance.17, 18 In our samples, we have verified the existence of the pyrrolyl b-protons by conducting NMR experiments Conclusions with the relaxation delay increased to 10 seconds, whereupon the d 6.15 b-proton signal reappears (Fig. 3c and the inset). Pyrrole and 3-alkylpyrroles were grafted to the precursor copolymers of PMMA and NPAMs by eVecting an oxidative Unlike the graft copolymers from unsubstituted pyrrole, the carbonyl band in FTIR spectra of the soluble graft copolymers polymerisation with FeCl3 in nitromethane.The electrical conductivity of the graft copolymers increases with increasing did not show any significant shift to lower wavenumbers with increasing content of 3APy (Table 1). This could be ascribable pyrrole or 3-alkylpyrroles content attaining ca. 10-4–10-3 S cm-1. The carbon chain lengths of the n-alkyl spacers to the formation of NH,ONC hydrogen bonding being disfavoured by the steric eVects of the n-alkyl pendants between pyrrole and the methacrylate groups in NPAMs had little eVect on the conductivity of the resultant graft copoly- attached.Similarly, steric eVects of the pendant chains which J. Mater. Chem., 1998, 8(11), 2347–2352 23515 A. O. Patil, A. J. Heeger and F.Wudl, Chem. Rev., 1988, 29, 183. mers, though longer alkyl spacers have an eVect of lowering 6 N. Toshima and S. Hara, Prog. Polym. Sci., 1995, 20, 155. the glass transition temperatures of the polypyrrole grafted 7 A. I. Nazzal and G. B. Street, J. Chem. Soc., Chem. Commun., copolymers. The graft copolymers of polypyrrole were insol- 1985, 375. uble, whilst the graft copolymers of 3-alkylpyrroles prepared 8 J.H. Han, T. Motobe, Y. E. Whang and S. Miyata, Synth. Met., from low NPAM-containing PMMA-co-PNPHMs and low 3- 1991, 45, 261. 9 G. Ruggeri, E. Spila, G. Puncioni and F. Ciardelli, Macromol. alkylpyrroles contents were completely soluble in common Chem., Rapid Commun., 1994, 15, 537. organic solvents even in their doped states. The introduction 10 V.Castelvetro, A. Colligiani, F. Ciardelli, G. Ruggeri and of long alkyl pendants onto the 3-position of pyrrole was M. Giordano, New Polymeric Mater., 1990, 2, 93. shown to have little influence on the conductivity of the 11 M. R. Simmons, P. A. Chaloner and S. P. Armes, Langmuir, 1995, resultant graft copolymers. 11, 4222. 12 (a) D. Stanke and M. L. Hallensleben, Synth. Met., 1993, 55–57, 1108; (b) D. Stanke, M. L. Hellensleben and L. Toppare, Synth. We thank the National University of Singapore for financial Met., 1995, 72, 89; (c) ibid., 1995, 73, 1; (d) ibid., 1995, 72, 61; support through the research grant RP960613. W.-L. Yu is (e) D. Stanke, M. L. Hellensleben and L. Toppare, Macromol. grateful to NSTB for a postdoctoral research fellowship and Chem. Phys., 1995, 196, 1697. 13 S.-K. Kang, W.-S. Kim and B.-H. Moon, Synthesis, 1985, 1161. J. F. Xia to NUS for the award of a research studentship. 14 J. Ruhe, T. Ezquerra and G. Wegner, Makromol. Chem., Rapid Commun., 1989, 10, 103. 15 E. P. Papadopoulos and N. F. Haidar, Tetrahedron Lett., 1968, References 14, 1721. 16 (a) D. Stanke, M. L. Hallensleben and L. Toppare, Synth. Met., 1 G. Tourillon, Handbook Of Conducting Polymers, ed. T. A. 1995, 72, 167; (b) D. Stanke, M. L. Hallensleben and L. Toppare, Skotheim, Marcel Dekker, NY, 1986. Synth. Met., 1995, 73, 267. 2 A. G. MacDiarmid and A. J. Epstein, Faraday Discussions, 1989, 17 G. L. Baker and F. S. Bates, Macromolecules, 1984, 17, 2619. 88, 317. 18 B. Bidan and M. Guglielmi, Synth. Met., 1986, 15, 49. 3 E. M. Genies, A. Boyle, M. Lapkowski and C. Tsintavis, Synth. Met., 1990, 36,139. 4 M. G. Kanatzidis, Chem. Eng. News, 1990, Dec 3, 36. Paper 8/06438E 2352 J. Mater. Chem., 1998, 8(11), 2347–2352