Polymer with liquid crystalline side chains

Polymers with Liquid Crystalline Side Chains... 

Extensive work has been done in a number of labora-toriesZ-lUL on the synthesis and characterization of several polymers with liquid crystalline side chains. Various of the papers in this monograph deal with various aspects of such polymers containing mesomorphic side chains. A review of the potential applications of such side chain liquid crystalline polymers therefore, will be redundant. 

Table I. Survey of some n-conjugated polymers with liquid crystalline side chains.

We chose a polyacrylate with liquid crystalline side chains as shown in Fig. 4. The family of this polymer with different alkyl spacers has been prepared by Ringsdorf and coworkers(25). Recently, they reported an interesting application of the following polymers for image recording(26-28) by means of the photoinduced phase transition principle. 

Small molecules with geometrical form-anisotropy and high polarizability may exhibit, besides the well-known crystalline and isotropic (liquid) phases, one or more liquid crystalline phases. If these molecules are attached to a polymer backbone, i.e. a polysiloxane chain by a flexible spacer, liquid crystalline phases are still present. The temperature range in which the liquid crystalline phases are stable may widen and liquid crystalline phases may even appear when the small molecular species exhibit only a crystalline phase. Studies with liquid crystalline side-chain polymers show that optical properties and the orientation function remain almost the same as compared to the small molecular species. 

Optical and electro-optical behavior of side-chain liquid crystalline polymers are described 350-351>. The effect of flexible siloxane spacers on the phase properties and electric field effects were determined. Rheological properties of siloxane containing liquid crystalline side-chain polymers were studied as a function of shear rate and temperature 352). The effect of cooling rate on the alignment of a siloxane based side-chain liquid crystalline copolymer was investigated 353). It was shown that the dielectric relaxation behavior of the polymers varied in a systematic manner with the rate at which the material was cooled from its isotropic phase. 

Estimate the characteristic temperatures of the liquid-crystalline side-chain polymer with the following structural unit ... 

SCLCPs combine liquid crystalline properties and polymeric behavior in one material. If the mesogenic unit is fixed directly to the polymer main chain, the motion of the liquid crystalline side chain is coupled with the motion of the polymer backbone, preventing the formation of a LC mesophase. Therefore, Finkelmann and Ringsdorf proposed that the introduction of a flexible spacer between the main chain and the mesogenic unit would decouple their motions, allowing the mesogenic moiety to build up an orientational order [29,30]. 

The liquid crystalline characteristics of cinnamate esters have been examined and novel azo bearing systems have been made based on 4-[N-ethyl-N-(2-methacryloyloxyethyl)]amino-4 -(2-cinnamoyloxyethylcarbonyl)-2 -(nitroazoben-zene). Poly[4-(2-methacryloylethoxy)azobenzene] has been found to be valuable for the photocontrol of liquid crystalline alignment as have polymers with benzylidene phthalimidine side chains. Poly(methyl methacrylates) with o-cinnamate side chains undergo polarisation isomerisation resulting in photoalign-... 

J. Stumpe, L. Muller, D. Kreisig, G. Hauck, H. D. Koswig, R. Ruhmann, and J. Rtibner, Photoreaction in mesogenic media, 5. Photoinduced optical anistropy of liquid-crystalline side-chain polymers with azodiromophores by linearly polarized light of low intensity, Makromol. 

The last volume is devoted to polymeric liquid crystals (with chapters about main-chain and side-group thermotropic liquid crystal polymers), amphiphilic liquid crystals, and natural polymers with liquid-crystalline properties. 

Yaroschuk O, et al. 2001. Light induced structures in liquid crystalline side chain polymers with azobenzene functional groups. J Chem Phys 114(12) 5330 5337. 

Stumpe J, Muller L, Kreysig D, Hauck G., Koswig HD, Ruhmann R, Rubner J. 1991. Photoinduced optical anisotropy of liquid crystalline side chain polymer with azochro mophores by low intensity of linearly polarized light. Makromol Chem Rapid Commun... 

Until now there was no obvious correlation found between the monomer structure and the resulting pol qner phase. No.theorr retical structural conditions were described which would result in a liquid crystalline polymer with a definite ordered phase e.g. with a nematic a smectic or a cholesteric phase as in conventional liquid crystals. Although previous examples have established (8 9) the existence of enantiotropic liquid crystalline side chain polymers additional considerations are in order for a systematic synthesis of such polymers. 

C. Noel and J. Virlet, "DSC, Miscibility and X-ray Studies of the Thermotropic Liquid Crystalline Polyesters with Aromatic Moieties and Flexible Spacers in the Main Chain", in "Liquid Crystals and Ordered Fluid, A. Griffin and A. Johnson eds., Plenvim Press, New-York, vol. 1+, 1+01 (198I+) Finkelmann, "Synthesis, Structure, and Properties of Liquid Crystalline Side Chain Polymers", in "Polymeric Liquid Crystals", A. Ciferri, W.R. Krigbaum and R.B. Meyer eds. Academic Press, New-York (I982)... 

The switching properties of liquid crystalline side chain polymers with either siloxane or acrylic groups as main chain are described, especially in relation to the possibility of dualfrequency addressing of fields effects. Also the optical birefringence data are reported. 

The liquid crystalline side chain polymers investigated have either a polysiloxane (compounds SiCl and SIGN) or a polyacrylic (compound AcCN) polymer chain. These are coupled via flexible spacers with the mesogenic p-substituted benzoic acid phenylester groups. SiCl and SiCN are copolymers with p-methoxy components in excess. 

Certain liquid crystalline side-chain polymers based on acrylate have been used as stationary phases for both liquid chromatography (LC) and GC [84,85]. The preparation of LCPs suitable for the separation of polychlorinated dibenzodioxins, dibenzofurans, and other polychlorinated aromatics has been described [86]. In addition, an extensive compilation of stationary phases for GC composed from LCPs with examples of applications have been presented in the literature [82]. 

Keith, C. Reddy, R. A. Tschierske, C. The first example of a liquid crystalline side-chain polymer with bentcore mesogenic units ferroelectric switching and spontaneous achiral symmetry breaking in an achiral polymer. Chem. Commun. 2005, 871-873. 

In Section III, liquid crystalline polyacetylene derivatives that have recently been developed will be reviewed as new types of conducting polymers with liquid crystalline functions in the side chain [1-9]. 

Figure 14 A schematic representation of cross-linking in liquid-crystalline side-chain polymers (adapted from T. Kato, H. Kihara, U. Kumar, T. Uryu, and J.M.J Frechet. Angew. Chem. Int. Ed. 33 1644-1645,1994. With permission).

Fig. 10. Cartoons depicting situations in which a spin-labeled polymer may yield the types of local director distribution shapes shown in Fig. 9. (a) Director perpendicular to polymer chain direction, determined by interactions between spin-label and liquid-crystalline side chains. Different ordering around two axes leads to the elongated distributions shown at the top of Fig. 9b Director parallel to main-chain direction, with spin label held at a fixed angle with respect to the chain, leading to the conical distributions shown at the bottom of Fig. 9.

It is perhaps appropriate to mention here that both nematic liquid crystalline side chain polymers with laterally attached mes-ogenic groups [16] and sanidic aromatic polyamides [17] have been shown to exhibit Nb phases. 

Chvalun SN, Blackwell J, Cho JD, Bykova IV, Percec V (1999) A second columnar liquid crystalline phase formed by polymers with highly tapered side chains. Acta Polym 50 (l) 51-66. doi 10.1002/(SICI)1521-4044(19990101)50 l<51 AID-APOL51>3.0.CO 2-0... 

Yaroschuk, O., Setgan, T., Lindau, J., Lee, S.N., Kelly, J., Chien, L.C. Light induced structures in liquid crystalline side-chain polymers with azobenzene functional groups. J. CJiem. Phys. 114(12), 5330-5337 (2001)... 

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