El Mostafa Moujahid

Fabrice Leroux

Jean-Pierre Besse

Marc Dubois

Comptes Rendus Chimie

Preliminary communication / CommunicationIn situ polymerisation of monomers in layered double hydroxidesEl Mostafa Moujahid, Fabrice Leroux, Marc Dubois, Jean-Pierre Besse *Laboratoire des matériaux inorganiques (UMR 6002 CNRS), université Blaise-Pascal, 63177 Aubière cedex, FranceReceived 6 March 2002; accepted 4 November 2002AbstractVinyl or amino-benzene sulfonates (VBS andABS) are polymerised in situ after a soft thermal treatment (T = 473 K) betweenthe sheets of layered double hydroxides (LDH). The reaction of polymerisation is studied either by13C CP- MAS NMR or ESRspectroscopies. The resonance peak associated to the vinyl group disappears from theVBS/LDH hybrid material, and conversely,a narrow signal, characteristic of free radicals, is observed for the ABS/LDH system.To cite this article: E.M. Moujahid, C. R.Chimie 6 (2003).© 2003 Académie des sciences. Published by E´ditions scientifiques et médicales Elsevier SAS. All rights reserved.RésuméLa polymérisation in situ de monomères tels que le vinyl benzene (styrène) sulfonate (VBS) et l’amino-3-benzène sulfonate(ABS), préalablement incorporés entre les feuillets d’une matrice d’hydroxyde double lamellaire, est effectuée par un traitementthermique modéré (T = 473 K). La réaction de polymérisation est vérifiée, pour VBS, par résonance magnétique nucléaire13C,en polarisation croisée et rotation à l’angle magique, avec la disparition de la liaison vinylique, et, pour ABS, par résonanceparamagnétique électronique, avec l’apparition d’un signal étroit caractéristique de radicaux libres dans les polymères conduc-teurs.Pour citer cet article : E.M. Moujahid, C. R. Chimie 6 (2003).© 2003 Académie des sciences. Published by E´ditions scientifiques et médicales Elsevier SAS. All rights reserved.Keywords: in situ polymerisation; layered double hydroxide;13C CP MAS and ESR spectroscopyMots clés : polymérisation in situ ; hydroxyde double lamellaire ; spectroscopies RMN13C de l’état solide et RPE1. IntroductionA great interest is actually devoted to the prepara-tion of nanocomposites. These multifunctional materi-als are usually built from a topotactic reaction betweena 2D host structure and a guest molecule [1,2]. Owingto the highly tuneable properties of their two constit-uents (for instance, thermoplasticity, insulative or con-ductive properties for the polymer, UV protection, de-lay in flammability from the inorganic host structurepoint of view), the nanocomposites find their applica-tions in a large number of fields, such as those empha-sising mechanical enhancement, gas permeability orpolymer electrolyte [3–7].In this study, we focussed our attention on the incor-poration of a polymer into the lamellar structure of* Corresponding author.E-mail address: jpbesse@chiimtp.univ-bpclermont.fr(J.-P. Besse).C. R. Chimie 6 (2003) 259–264© 2003 Académie des sciences. Published by E´ditions scientifiques et médicales Elsevier SAS. All rights reserved.DOI: 10.1016/S1631-0748(03)00002-Xlayered, double hydroxides. The latter are made ofsheets of edge-sharing metal octahedra where, by com-parison to brucite M(OH)2, a fraction of the divalentmetal cations (M) is replaced by trivalent cations (M').The excess of charge, i.e. M', is counterbalanced byinterlayered anions, leading to an anionic exchangecapacity. Two LDH materials M2M' (OH)6Cl·2 H2O,where (M, M') = (Zn, Al) and (Cu, Cr) are designed asthe inorganic host framework.Direct polymer incorporation is hampered by theadsorption on crystallites, thus limiting the diffusionbetween the layers. Therefore, the polymerisation ofthe interleaved monomer is an appropriate method, asillustrated by several systems such as pyrrole/V2O5xerogel [8], aniline/RuCl3 [9], etc., although in situpolymerisation requires usually low pH or/and the useof an external oxidising agent, such as (NH4)2S2O8 orFeCl3. LDH material is plagued by these two condi-tions, as it dissolves at low pH, and it presents a greataffinity for the counter-anions of the oxidising agent,thus back-exchanging the monomer [10]. An alterna-tive method consists of synthesising the LDH materialin the presence of the polymer, the so-called ‘ templat-ing method’ . However, this method gives rise to ill-defined solids [11].We present an easy pathway to reach in situ poly-merisation. First, the monomers, vinyl or amino-benzene sulfonate (called VBS and ABS), are incorpo-rated by an anion exchange reaction from the chlorineanions present between the LDH sheets. A soft thermaltreatment is then applied to the monomer/LDH deriva-tives. Recently, this process was found to induce thepolymerisation of aniline carboxylic acid in the galler-ies of a LiAl2(OH)6Cl·H2O hydrotalcite-type sample[12], the pristine material being, however, partiallyexchanged with the monomer. In the present contribu-tion, the in situ polymerisation of VBS and ABSbetween the layers of LDH materials are characterisedby 13C CP-MAS NMR and ESR spectroscopies, re-spectively.2. Experimental section2.1. PreparationThe starting LDH substrates M2M' (OH)6Cl·n H2Owere prepared using a coprecipitation method for(M, M') = (Zn, Al) [13] and the ‘salt and oxide disso-lution’ synthesis for (M, M') = (Cu, Cr) [14]. For thefirst method, a solution of ZnCl2 (2 M) and AlCl3 (1 M)was slowly added to decarbonated water under a vig-orous stirring at a constant pH of 9. For the second, 250cm3 of CrCl3 (10–2 M) were added dropwise to asuspension of copper oxide (CuO) (20 mmol; grainsize z 5 mm; Aldrich). In each case, the slurry wasaged overnight, centrifuged and then washed severaltimes with decarbonated water and finally dried atroom temperature.For the exchange reactions from the chlorideanions, the quantity of monomer corresponded to twicethe exchange capacity. VBS (CH= CH2–C6H4SO3H,Aldrich 99% purity grade) and ABS (NH2–C6H4SO3H, 97%, Aldrich) were used as received. Theexchange capacity is of 270 and 290 mequiv/100 g for(M, M') = (Cu, Cr) and (Zn, Al), respectively. Theexchange reaction time was 24 h. The resulting powderwas separated as described above.Elemental analysis was performed at the VernaisonAnalysis Centre of CNRS by using the inductive con-duction plasma coupled to atomic emission spectros-copy (ICP/AES) technique.2.2. InstrumentationX’Pert Pro Philips equipped with a HTK16 AntonPaar chamber and a PSD-50m Braun detector was usedto record XRD diagrams. The conditions were: stepwidth of 0.0387 °, time per step of 60 s, and an apertureof 2 ° (155 channels).ESR spectra were recorded using an X Band BrukerEMX spectrometer equipped with a standard variabletemperature accessory and operating at 9.653 GHz atTable 1Chemical compositions of LDH and derivative materials reportedper (OH)2.Sample CompositionZn2Al/Cl Zn0.67Al0.33(OH)2Cl0.33·0.75 H2OCu2Cr/Cl Cu0.68Cr0.32(OH)2Cl0.33·0.92 H2OZn2Al/VBS Zn0.67Al0.33(OH)2(CH2CHC6H4SO3)0.33Cle·0.78 H2OCu2Cr/ABS Cu0.67Cr0.33(OH)2(C6H4NH2SO3)0.32Cle·0.85 H2OElemental analyses (weight in% for 100 g): for Zn2Al/Cl: Zn:38.94%, Al: 8.04%, Cl: 10.57% H: 3.12%. For Cu2Cr/Cl: Cu:34.71%, Cr: 14.18%, Cl: 9.69%, H: 3.14%. For Zn2Al/VBS: Zn:27.06%, Al: 5.58%, Cl: 0.32%, H: 3.62%, S: 6.62%. ForCu2Cr/ABS: Cu: 25.33%, Cr: 10.26%, Cl: 0.45%, H: 2.91%, N:2.79%.260 E.M. Moujahid et al. / C. R. Chimie 6 (2003) 259–264room temperature and at 9.411 GHz when the tempera-ture accessory is set up. Diphenylpicrylhydrazyl(DPPH) is used to determine the resonance frequency(g = 2.0036 ± 0.0002).13C solid-state NMR experiments were performedon a 360 Brüker spectrometer at room temperaturewith a 4-mm diameter zirconia rotor. To enhance thesensitivity of the nucleus, cross-polarisation (CP) tech-nique was performed. Under a spin-locking of theprotons, the conditions of Hartmann–Hahn are ap-plied. 13C CP-MAS NMR spectra were obtained at75.46 MHz, 1H 90 °, with a pulse width of 4.7 µs, a CPtime of 1.5 ms, and a recycling time of 3 s. Thechemical shift was calibrated with the carbonyl ofglycine at 176.03 ppm. The spinning condition was 10kHz.Electrochemical measurements were performed in athree-electrode cell, with acetonitrile (ACN) andLiClO4 (0.5 M) as electrolyte. The counter- and refer-ence electrodes were in platinum. The experimentswere carried in potentiostatic mode, with steps of50 mV s–1, and measured with a Princeton EGG–273apparatus. The composite working electrode depositedon Pt grid is based on 80, 10, and 10% in weight ofactive material, carbon black, and polyvinylidene dif-luoride, respectively.3. Results and discussionThe chemical analyses are reported in Table 1. Forthe chlorine LDH pristine material, noted as Zn2Al/Cland Cu2Cr/Cl, the ratio between the two cationsmatches the nominal 2:1 value, showing that the reac-tion of formation is completed. The exchange reactionswith the organic molecules, VBS and ABS, are alsocompleted, since the chloride anions are present astraces only. The monomer-modified LDH materials arenoted Zn2Al/VBS and Cu2Cr/ABS.The powder X-ray diffraction patterns ofMM'(OH)6Cl·n H2O, (M, M') = (Zn, Al) or (Cu, Cr) arecharacteristic of the LDH structure [14]. The patternwas refined using R3m space group in rhombohedralsymmetry (eight distinct dhkl distances were indexed).The cell parameters a and c (equal to three times theinterlamellar distance, c = 3 d(003)) are 3.07 and23.28 Å, respectively, for [Zn2Al–Cl], and 3.11 and22.53 Å for [Cu2Cr–Cl]. The exchange of the chlorineanions by the monomer molecules increases the basalFig. 1. In situ XRD patterns of (1) LDH pristine and monomerderivatives at (2) 25 °C and (3) 200 °C for the materials (a)Zn2Al/VBS and (b) Cu2Cr/ABS. The asterisk corresponds to PSDsystem. The Miller indexing is given.261E.M. Moujahid et al. / C. R. Chimie 6 (2003) 259–264spacing, d(003), of the host structure, from 7.76 to18.04 Å for the incorporation of VBS between [Zn2Al]sheets, and from 7.51 to 15.35 Å for ABS between[Cu2Cr] (Fig. 1). The values are consistent with twolayers of monomer on each side of the interlamellargallery.A soft thermal treatment was applied for 4 h, at 160and 180 °C, to the monomer-modified LDH materials;they are then called Zn2Al/VBS-T and Cu2Cr/ABS-T.For the former, the colour turns from white to yellowand, for the latter, pale green to dark brown. Theharmonics (00l) for the two materials become broader,and a decrease in the interlayer distance, d(003), isobserved, down to 14.46 and to 12.71Å for the nano-composites Zn2Al/VBS-T and Cu2Cr/ABS-T, respec-tively (Fig. 1). A similar contraction of the lamellarstructure was observed for the in situ polymerisation ofa,b-aspartate into hydrotalcite-type compounds [15].To elucidate whether or not the polymerisation doesoccur after the thermal treatment, 13C CP–MAS NMRand ESR spectroscopies are employed to scrutinise thenanocomposites Zn2Al/VBS-T and Cu2Cr/ABS-T, re-spectively.The 13C CP-MAS spectrum of VBS/Zn2Al beforeand after thermal treatment is displayed in Fig. 2. Theresonance peaks for the VBS molecule C1H2= C2H-Fig. 2. 13C CP- MAS spectra. Assignment of the resonance peaks is indicated in the text.262 E.M. Moujahid et al. / C. R. Chimie 6 (2003) 259–264C3(C44H4)C5–SO3 are assigned as follows: C1,113.9 ppm; C2, 137.4 ppm; C3, 141.5 ppm; C4, 125ppm; C5, 143.8 ppm. When incorporated between[Zn2Al] LDH sheets (no heat treatment), some reso-nance peaks are shifted; this corresponds to a shieldingeffect for C2, C3, and C5. This is explained by theelectrostatic interaction between SO3 function and theLDH surface, thus weakening the electrophilic charac-ter toward C5. The effect propagates through the ben-zene backbone down to C1, which is downfield shifted.After the treatment, the resonance peaks of the materialresemble that of poly(styrene) sulfonate, noted as PSS,with the disappearance of C1 and the formation ofhumps located at ~40–50 ppm, characteristic of –CHand –CH2 responses. In the meantime, C3 is shifted, asexpected in the absence of the vinyl group. Undoubt-edly, it means that VBS monomers have been polymer-ised between Zn2Al LDH layers.ESR measurements are conducted for the nanocom-posite ABS/Cu2Cr hybrid (Fig. 3). In addition to theLDH response (associated with a peak-to-peak lin-ewidth, noted as DHpp, close to 1100 ± 20 G(g = 2.0621 ± 0.0005), a narrow signal appears at 393K (DHpp = 30 ± 4 G), associated with a g value of2.0034 ± 0.0004. This value is in the range commonlyobserved for organic radicals and/or conduction elec-trons and comparable to what is found for other relativesystems, such as PANI intercalated in layered perovs-kite [16]. When the thermal treatment is performed inthe absence of air, the narrow signal is absent. Addi-tionally, the molecules ABS do not provide such asignal in temperature, pointing out the importance ofthe confinement supplied by LDH framework.The presence of a quinoid structure in the nanocom-posite ABS/Cu2Cr-T was confirmed by a FTIR study,with the presence of a vibration band at 1597 cm–1[17].To further ascertain results, the electrochemical be-haviour of the material Cu2Cr/ABS-T is studied in anaprotic solvent (Fig. 4). The anodic sweep is character-ised by a peak at Va = –800 mV/Pt. The current peak isascribed to the quasi-reversible oxidation of leucoem-eraldine to emeraldine [18]. In contrast, the pristinematerial Cu2Cr/Cl exhibits a featureless capacitive re-sponse (Fig. 4).The electropolymerisation of the materialCu2Cr/ABS was also studied. On the anodic sweep,two current peaks are observed, the peak at –750 mV isascribed to the p-doping of the polymer [18], the re-versible response at –280 mV (and Vc = –550 mV,marked by an asterisk) is associated to the stabilisationof dimers [19].As reported by other authors, the polymerisation ofan amino ring-substituted monomer may then beachieved in hydrophobic solvent [20, 21], although, inour case, it is accompanied by the formation of dimers.Moreover, the absence of the electrochemical responseof dimer confirms the efficiency of the thermal treat-ment for the polymerisation process.4. ConclusionWe demonstrate that in situ polymerisation may beachieved within the interlayered space of non-oxidising LDH host structure by a soft heat treatment.Fig. 3. In situ derivative ESR signal of the material Cu2Cr/ABS at(a) 273 K and (b) 413 K recorded with a sweep width of 6500 G. Ininset, the spectra are recorded with a sweep width of 150 G tomagnify the narrow signal (receiver gain: 5000).263E.M. Moujahid et al. / C. R. Chimie 6 (2003) 259–264In the present contribution, it is exemplified by thenanocomposites Zn2Al/VBS and Cu2Cr/ABS. The or-ganic–inorganic materials are characterised by a com-bination of techniques.References[1] C.O. Oriakhi, J. Chem. Educ 77 (2000) 1138.[2] P. Gomez-Romero, Adv. Mater. 13 (2001) 163.[3] S.J. Komarni, Mater. Chem. 2 (1992) 1219.[4] E. Ruiz-Hitzky, Adv. Mater. 5 (1993) 334.[5] E. Giannelis, Adv. Mater. 8 (29) (1996).[6] H. Ishida, S. Campbell, J. Blackwell, Chem. Mater. 12 (2000)1260.[7] F. Leroux, J.-P. Besse, Chem. Mater. 13 (2001) 3507.[8] M.G. Kanatzidis, C.G. Wu, H.O. Marcy, D.C. DeGroot,C.R. Kannewurf, Chem. Mater. 2 (1990) 222.[9] L. Wang, P. Brazis, M. Rocci, C.R. Kannewurf, M.G. Kanatzi-dis, Chem. Mater. 10 (1998) 3298.[10] S. Rey, J. Mérida-Robles, K.S. Han, L. Guerlou-Demourgues,C. Delmas, E. Duguet, Polym. Int. 48 (1999) 277.[11] C.O. Oriakhi, I.V. Farr, M.M. Lerner, Clays, Clay Miner. 45(1997) 194.[12] V.P. Isupov, L.E. Chupakhina, M.A. Ozerova, V.G. Kostro-vsky, V.A. Poluboyarov, Solid State Ionics 231 (2001)141–142.[13] S. Miyata, Clays Clay Miner. 31 (1983) 305.[14] A. De Roy, C. Forano, K. El Malki, J.-P. Besse, in: L. Occelli,H. Robson (Eds.), Synthesis of Microporous Materials, Rein-hold, Van Nostrand, 1992.[15] N.T. Whilton, P.J. Vickers, S.J. Mann, Mater. Chem. 7 (1997)1623.[16] S. Uma, J. Gopalakrishnan, Mater. Sci. Eng. B 34 (1995) 175.[17] M. Moujahid, M. Dubois, J.-P. Besse, F. Leroux, Chem. Mater.14 (2002) 3799.[18] W.S. Huang, B.D. Humphrey, A.G. MacDiarmid, J. Chem.Soc., Faraday Trans, 82 (1986) 2385.[19] K.L.N. Phani, S. Pitchumani, S. Ravichandran, Langmuir 9(1993) 2455.[20] M.C. Miras, C. Barbero, R. Kötz, O. Haas, J. Electrochem.Soc. 138 (1991) 335.[21] K. Yamada, K. Teshima, N. Kobayashi, R. Hirohashi, J. Elec-troanal. Chem. 394 (71) (1995).Fig. 4. Cyclic voltammograms for the materials Cu2Cr/Cl, Cu2Cr/ABS, and Cu2Cr/ABS-T. The asterisks (*) indicate the response of the dimers(see text).264 E.M. Moujahid et al. / C. R. Chimie 6 (2003) 259–264

In situ polymerisation of monomers in layered double hydroxides

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In situ polymerisation of monomers in layered double hydroxides

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