J. MATER. CHEM., 1994, 4(8), 1351-1352 First Ferrocene-containing Side-chain Liquid-crystalline Polymers Robert Deschenaux,*a Isabelle Kosztics: Ulrich Scholten," Daniel Guillonb and Mohammed Ibn-Elhajb a Universite de Neuchitel, lnstitut de Chimie, Av. de Bellevaux 57,2000 Neuchitel, Switzerland lnstitut de Physique et Chimie des Materiaux de Strasbourg, Groupe des Materiaux Organiques, 23 Rue du Loess, B.P.20 CR, 67037 Strasbourg Cedex, France The synthesis and mesomorphic properties of the first ferrocene-containing side-chain liquid-crystalline polymers, obtained by grafting either a 1,l'-or 1,3-disubstituted ferrocene derivative functionalized by a vinyl group onto a polysiloxane, are reported; these polymers showed enantiotropic smectic C and/or smectic A phases.Increasing interest is currently devoted to metal-containing latter materials showed only limited properties: ;I nematic thermotropic liquid-crystalline polymers. The incorporation melt was observed at elevated temperatures (isotropization of a metal centre into mesomorphic materials capable of temperatures were not reported); furthermore, these com-forming films or fibres could lead to a source of processable pounds were found to be insoluble in most solvents. materials exhibiting new magnetic, optical and electronic Obviously, new structures are required to rationalize the properties.' structure-mesomorphic property relationship for metal-Main-chain and side-chain coordination liquid-crystalline containing liquid-crystalline polymers. polymers have attracted most attention so far.2 Interesting We report herein the synthesis and mesomorphic behaviour magnetic studies were made with a copper-containing nematic of ferrocene-containing monomers 1 and 2 and of side-chain polyester.2" A series of main-chain polyesters incorporating polysiloxanes 3 and 4.Ferrocene-containing side-chain liquid- These crystalline polymers have not been described previously. The the ferrocene unit in their backbone was also rep~rted.~ 1 CH3I (CH3)3Si-(SiO),-Si(CH3)3I H 5 e 2 6 CH3 (CH&3iO-I Si(CH& c 0 2 0 c o Z e OC 1eH37 I(CH,), ,o~ C O ~ ~ O ~ C ~ 3 4 mesomorphic properties of 1-4 were investigated by differen- tial scanning calorimetry (DSC), polarized optical microscopy and X-ray diffraction studies.1 and 2 were prepared from either ferrocene-1,l'-diacid chloride4 or ferrocene-1,3-diacid chloride5 and the appropriate phenol derivatives6 following a stepwise procedure we recently developed for synthesizing unsymmetrically 1,l'- and chiral 1,3-disubstituted ferrocene-containing thermotropic liquid cry~tals.~The structures of 1 and 2 were confirmed by 'H NMR spectroscopy and elemental analysis. The 1,l'-disubstituted ferrocene derivative 1 exhibited enantiotropic smectic C and smectic A phases (c'124's,'13l.sA'141.I).On heating, the 1,3-disubstituted ferrocene derivative 2 showed an enantiotropic smectic A phase (C.168.SA.201*I). On cooling from the isotropic melt, a monotropic smectic C phase also formed at 160 "C after the smectic A one.Ferrocene derivative 2 melted at a higher temperature than its 1,l'-isomeric ana- logue l. This result can be explained from the X-ray crystal structure obtained for a 1,3-disubstituted ferrocene derivative which revealed that such a substitution leads to highly aniso- metric structures' as compared to the 'step' structure of ferrocene derivatives substituted in l,l'-positi~ns.~ Polymers 3 and 4 were synthesized by grafting of monomer 1 or 2 onto polysiloxane 5 (Huls America Inc., no. PS 120; M =2270) or 6 (Huls America Inc., no. PS 123.5; m= 15-18%, n =82-85%; M =2000-2500), respectively, following a litera- ture procedure" [toluene, 70 "C, 24 h; PtC12( 1,5-C,Hl2); 1.1 equiv.of monomer]. The ratio of substitution is not yet known; however, the strong decrease of the Si-H bond peaks in the reaction as followed by 'H NMR spectroscopy (4.7 ppm, CDC1,) and IR spectroscopy (2160 cm-', KBr), revealed that a high content of monomeric unit was anchored onto the polysiloxane. The bulkiness of the ferrocene unit may have prevented the reaction from going to completion. Polysiloxanes 3 and 4 showed good solubility in common organic solvents (CH,Cl,, CHCl,, THF, toluene). Purification was accomplished by addition of methanol into a CH,Cl, solution followed by centrifugation to recover the precipitated polymer. After several purification cycles, the polymer was obtained in ca. 40% yield. Absence of unreacted monomer was confirmed by gel permeation chromatography (Ultrastyragel, THF).Molecular weight determination of the synthesized polymers is currently under investigation (unsatis- factory results have been obtained so far using GPC with polystyrene standards to calibrate the columns). Polymeric structures 3 and 4 presented interesting meso- morphic behaviour. On heating, both compounds gave rise to a birefringent melt between the crystal state and the isotropic liquid. No decomposition was detected. As is often the case with polymers, the mesophases could not be identified by polarized optical microscopy: owing to the high viscosity of these materials, typical textures cannot develop." However, an unambigous characterization of the liquid-crystalline phases was provided by means of X-ray diffraction analyses which revealed that polymer 3 exhibited enantiotropic smectic C and smectic A phases (c.13o.sc.148.sA.171.I) and polymer 4 presented an enantiotropic smectic A phase (C-146.SA.2O2-I).Therefore, the polymeric structures retained the mesophases J. MATER. CHEM.. 1994, VOL. 4 shown by their corresponding low-molar-mass ferrocene derivative. Note that the polymers exhibited a broader aniso- tropic domain than the monomers (41 "C for 3 and 17 "C for 1; 56 "C for 4 and 33 "C for 2). In the smectic A phase, the d-layer spacine calculated from X-rax diffraction data was found to be 54.5 A (at 160°C) and 64.8 A (at 170"C) for 3 and 4, resptctively. Since CPK models gave a molecular length L of 68.5 A for 1 and 2 (in their fully extended conformation), a d/L ratio of 0.80 and 0.95 was obtained for 3 and 4, respectively.These data suggest a monolayer organization of the monomeric units with a pro- nounced disorganized molecular arrangement in the case of 1. In conclusion, polymers 3 and 4 showed pronounced liquid- crystal character, high thermal stability and good solubility in organic solvents. This combination of properties makes ferrocene-containing side-chain liquid-crystalline polysilox- anes interesting materials for the development of electroactive liquid-crystalline polymers. Finally, owing to the planar chiral- ity of monomeric unit 2, due to the substitution of the 1,3-positions by two different sub~tituents,~~ polymer 4 is also chiral.To our knowledge, this is the first example of a chiral metal-containing liquid-crystalline polymer. 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