Liquid crystallinity ferrocene polymers

Research into liquid-crystalline ferrocene sidechain polymers has been conducted by the research groups of Zentel and Deschenaux. One such liquid-crystalline polymer, polymethacrylate (18) and its monomer, showed enantiotropic smectic C and smectic A phases. This polymer also exhibited a weight average molecular weight of 100,000. ... 

Senthil and Kannan have also reported the synthesis of liquid crystalline ferrocene-based polymers containing phosphate groups in their backbones. The molecular weights of these polymers were relatively low however, they had very narrow polydispersities. Scheme 26 shows the synthesis of polymers 106 by the polycondensation of 104 with 105. The polymers with 8 and 10 methylene spacers in their backbones possessed clear nematic textures, while most of the other polymers with shorter aliphatic chains had a grainy texture. Only the polymer with ethylene spacers and a pendent phenyl group did not show anisotropic behavior. 

Except for the structure containing 100% of ferrocene unit, which decomposed before melting, all the organometallic copolymers exhibited birefringent melts. Nematic textures were identified by means of polarized optical microscopy and, in one case, by X-ray diffraction studies. For comparison purposes, a polymer without ferrocene unit was prepared, but showed no mesomorphism. The authors deduced that the ferrocene framework was contributing to the liquid crystallinity of the ferrocene-containing polymers. 

Ferrocene-containing liquid crystalline polymers 30 have been reported from the solution polymerization of l,T-bis(chlorocarbonyl)ferrocene, terephthaloyl chloride, and methylhydroquinone in refluxing dichloromethane [38], as indicated in Scheme 10-11. With one exception, these ferrocene containing copolyesters were reported to have birefringent melts. The presence of liquid crystallinity was verified by differential scanning calorimetry (DSC), polarized light microscopy, and X-ray diffraction studies. 

Gao et al. have recently prepared a number of thermotropic liquid crystalline main-chain fer-rocenes exhibiting fluorescent properties.182 The reaction of 1,1 -bisf functionalized)ferrocenes, 95, with 1,4-dibromobutane, 97a, or a,a -dibromo-p-xylene 97b generated polyelectrolytes 97a,b with Mn ranging from 5400-14,700 (Scheme 2.29). These polymers were highly thermally stable with the first weight loss occurring between 172 and 330°C. The liquid crystalline properties showed these materials formed smectic liquid-crystal phases and displayed batonnet textures. 

Senthil and Kannan prepared ferrocene-based liquid crystalline polymers containing phosphate groups in the backbone.191,192 The majority of these polymers showed grainy nematic textures, whereas polymers with 8 and 10 methylene groups in the backbone displayed clear nematic textures. Liquid crystalline behavior was not observed for the polymer incorporating both ethylene spacers and a pendent phenyl group. 

Liquid crystalline polymers containing ferrocene in their side chains have been reported.235-240 Deschenaux used free-radical synthesis to prepare thermotropic liquid crystalline polymethacrylates containing ferrocene (Scheme 2.46).235 Polarized light microscopy showed that monomer 171 and its corresponding polymer 172 exhibited enantiotropic smectic A and C phases. 

Deschenaux and co-workers also isolated liquid crystalline polysiloxanes containing ferrocene in their side chains.236 These polymers contained either 1,3- or l,l -disubstituted ferrocene and were synthesized from the reaction of preformed polysiloxanes and vinyl organo-iron monomers. 

This type of approach has been extended to main-chain liquid crystalline polymers 26 with low loadings of ferrocene groups in the side-group structure. In some cases, changes in liquid crystalline morphology from nematic to smectic were observed upon oxidation, as the formation of ionic domains facilitates the generation of layered structures (Figure... 

Liu X H, Bruce DW, Manners I. 1997. Novel calamitic side chain metallomesogenic polymers with ferrocene in the backbone S5mthesis and properties of thermotropic liquid crystalline poly(ferrocenylsilanes). Chem Commun (3) 289 290. 

The section commences with monosubstituted ferrocene derivatives, after which the influence of the substitution pattern on the formation and stability of liquid-crystalline phases for disub-stituted ferrocene derivatives will be discussed. Next, the influence of the three-dimensional structure of ferrocene on the mesomorphic properties will be highlighted, optically active ferrocene materials will be described and, finally, ferrocene-containing liquid-crystalline dendrimers will be introduced ferrocene-containing liquid-crystalline polymers will not be reported. Note that a review devoted to ferrocene-containing thermotropic liquid crystals has already been published. ... 

The redox properties of the ferrocene unit were also used to control the liquid-crystalline organization of side-chain liquid-crystalline poly(methacrylates) the reduced polymer gave rise to smectic C and smectic A phases whereas the oxidized polymer showed a nematic phase. ... 

Ferrocene was the starting point for organometallic chemistry nearly four decades ago and is still today one of the most studied and versatile organometallic building blocks. Ferrocene has been incorporated in polymeric systems to alter bulk properties of the material. Ferrocene possesses excellent thermal and photochemical stability and can also protect polymeric systems from photodegradation. In addition, the ferrocene building block has been used in conducting polymers and in main chain liquid crystalline polyesters. ... 

It has also been reported that polymers containing ferrocene units in the main-chain or sidechains may possess liquid crystalline characteristics. " Ferrocene-based liquid crystalline polyesters (3) containing phosphorous groups in their backbones have been reported by Senthd and Kannan. ... 

Research in metallocene-containing polyamides, polyureas, polyuretiianes, and polyesters continued to be conducted in the 1980s, and since that time, research into these classes of materials has continued to grow7 Homoannular and heteroaimular liquid-crystalline polymetallocenes have been prepared by Zentel and coworkers through condensation reactions. Ferrocene-based liquid-crystalline polymers have also been reported by Senthil and Kannan. The synthesis of ferrocene polymers containing backbone organophosphorus moieties 32 is shown in scheme 9. 

Synthesis and mesomorphic properties of the first ferrocene-containing side-chain liquid crystalline polymers, 69, obtained by grafting either a 1,1 - or a 1,3-disubstituted ferrocene derivative functionalized by a vinyl group onto a polysiloxane have been reported [155J. These polymers showed enantiotropic SmC and/or SmA mesophases. 

Chiral phosphorus-containing dendrimers which have ferrocene molecules at the periphery have been the subject of work by Majoral and co-workers. These materials will have obvious applications in catalysis. Layer-by-layer dendrimers, which are built up containing chiral ferrocenylphosphine molecules, have also been prepared, and their chiroptical and electrochemical properties have been investigated. A recent article covers the basic chemistry of ferrocene-containing liquid-crystalline polymers which stems from the extensive work of Deschenaux, who essentially pioneered the area. A ferrocene end-capped dendrimer has also been used in carbon monoxide sensing. The actual dendrimer, shown as 19, has 48 ferrocene molecules on the periphery. 

Polymerization of organoiron monomers has also resulted in the production of liquid crystalline polymers containing ferrocene units in their sidechains. " Scheme 6 illustrates Deschenaux s free-radical synthesis of ferrocene functionalized thermotropic liquid crystalline polymethacrylates Monomer 31 and its corresponding polymer 32 exhibited enantiotropic smectic A and C phases. 

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