Ferroelectric liquid crystalline polymers side chain

Ferroelectric side chain liquid crystalline polymers have been synthesized recently. Because of their non-central symmetry they don t need to be poled. This has led to the recent active research efforts in the field of ferroelectric side chain liquid crystalline polymers (Guglielminetti et al., 1990 Spassky et al., 1989 Kapitza et al., 1986). 

Naciri, J., Pfeiffer, S., and Shashidhar, R., Fast switching ferroelectric side chain liquid-crystalline polymer and copolymer, Uq. Cry.%t., 10, 585-591 (1991). 

Reorientation Dynamics of a Ferroelectric Side-Chain Liquid-Crystalline Polymer in a Polarity-Switched Electric Field... 

Naciri J, Pfeiffer S, Shashidhar R (1991) Fast switching of ferroelectric side-chain liquid-crystalline polymer and copolymer. Liq Cryst 10(4) 585-591. doi 10.1080/02678299108036446... 

Ferroelectric liquid crystals (FLC) have attracted attention because of their high speed response and memory effect (7-5). The characteristics of fast response and memory effect make them suitable in electro-optical device applications, such as display, light valve and memory devices. Ferroelectric side chain liquid crystalline polymers (FLCPs) exhibit desirable mechanical properties of polymers and electro-optical properties of low molecular weight FLC, which have been investigated extensively Corresponding author. 

It is difficult to grow a good organic crystal film and a Langimur-Blogette film of up to 1 micron thickness. However, polymers have a wide choice and can be tailored to meet the above requirements. The polymers may be side chain liquid crystalline polymers, ferroelectric liquid crystalline polymers and amorphous polymers. Among them the side chain liquid crystalline polymers have drawn more attention. 

It has been found experimentally that the spontaneous polarization Ps of side chain liquid crystalline polymers is more or less the same as that of small molecular mass liquid crystals, i.e., so far as the chemical formula of the side group of a side chain liquid crystalline polymer is the same as that of a small molecular mass liquid crystal. This phenomenon illustrates that either the side groups in the side chain liquid crystalline polymer or the small molecular mass ferroelectric liquid crystal in their Sc phase are aligned in same way. The dependence of Ps on temperature for the three small molecular mass ferroelectric liquid crystals LI, L2 and L3 and their polymer counterparts PI, P2 and P3 are depicted in Figure 6.40. 

Boemlburg et al. (1991) first discovered the anti-ferroelectric liquid crystal phase in the chiral side chain liquid crystalline polymer, Sca phase. Several other research groups followed with more such side chain liquid crystalline polymers. Boemlburg et al. (1992) reported an anti-ferroelectric liquid crystal in the molecule... 

Vallerien SU, Zentel R, Kremer F, Kapitza H, Fischer EW (1989) Ferroelectric modes in combined side-group main chain liquid-crystalline polymers. Makromol Chem Rapid Commun 10(7) 333-338... 

S. U. VUIerien. R. ZenteL F. Kremer, H. Kapttza, and B. H. Fisdicr, Ferroelectric modes in combined side gro q> main chain liquid crystalline polymers. MakromoL Chem. Rapid Comimm. 10 335 (1969). 

Shibaev et al. (1984) first synthesized a ferroelectric side chain polymeric liquid crystal. In the following years a lot of liquid crystalline polymers of such kind were synthesized. In early research studies techniques used to understand polymers and whether they showed the liquid crystal phase were limited so that the conclusion was ambiguous. It was only in 1988 when Uchida et al. (1988) measured the spontaneous polarization and the tilt angle that people became convinced that this side chain polymer in the literature (Shibaev et al., 1984) is indeed a ferroelectric liquid crystal. 

The side chain polysiloxane liquid crystalline polymers PI, P2 and P3 composed of the above three ferroelectric liquid crystals as the side groups exhibit the ferroelectric liquid crystal phase, their chemical formulae being respectively. 

For the small molecular mass ferroelectric liquid crystal when reversing the polarity of the applied electric voltage the molecules rotate locally while their molecular mass centers don t necessarily move accordingly. But for side chain ferroelectric liquid crystalline polymers, as one of the side group ends is confined to backbone, shown in Figure 6.43, the polarity reversion must be accompanied by the movement of their mass centers, which causes a backflow in order to re-distribute the mass centers. Moreover, the side groups may collide with each other. The effect results in the displacement of the backbone. The above effects increase the difficulty of re-orientation and hence increase the viscosity. 

Endo et al. (1992) measured the optical transmission and the polarity-reverse current during the polarity reversion of a side chain ferroelectric liquid crystalline polymer. It was found that both parameters reached peak values at the same time. It was concluded that the rigid core of the side groups responsible for birefringence moves simultaneously with the dipole moment reversion and the latter contributes to the polarity reversion current. The FTIR experiment suggested that the backbone moves when the polarity is reversed. 

Mesogenic groups can be incorporated into polymeric systems [7]. This results in materials of novel features like main chain systems of extraordinary impact strength, side-chain systems with mesogens which can be switched in their orientation by external electric fields or—if chiral groups are attached to the mesogenic units—ferroelectric liquid crystalline polymers and elastomers. The dynamics of such systems depends in detail on its molecular architecture, i.e. especially the main chain polymer and its stiffness, the spacer molecules... 

The molecule is a liquid crystalline polymer with chiral smectic C phase forming parts attached as side chains. The field required to switch the direction of polarization of the polymer is very low (0.3 MVm ). There is a lot of interest in liquid crystalline ferroelectric polymers, because of their possible use for fast-switching electro-optical devices. More information about ferroelectric liquid crystals can be found in references [36,37]. 

The author s group chose polyacrylate [102, 103], polyoxyethylene [104, 105], polysiloxane [103], and a polyacrylate/polysiloxane hybrid polymer [106] as the main chain according to the design in Fig. 1.26b-e. We attached various kinds of side-chain structures onto polymer main chains described above and checked the physical properties of these side-chain-type ferroelectric liquid crystalline polymers (FLCPs). 

In addition to investigating ferroelectric liquid crystalline conjugated polymers with dynamic switching functionahties under an electric field, our group has also developed photoresponsive liquid crystalline conjugated polymers with dynamic switching of linearly and circularly polarized luminescence. This was accomplished through the use of a photoisomerizable moiety in the polymer side chain. 

Recently, liquid-crystalline polyphenylene derivatives have been synthesized through substitution of a fluorine-containing chiral liquid-crystalline group into side chains, with an aim to develop ferroelectric liquid-crystalline conjugated polymers (Fig. 5 Suda and Akagi 2008). These are attracting interest because they can afford anisotropies in electrical and optical properties when they are macroscopically aligned. This study also elucidated that PPP can be used to prepare new types of polymer materials. 

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. 

Svensson, M., Helgee, B., Skarp, K., Hermann, D., and Andersson, G., Chiral liquid crystalline side-chain polymers effects of side-chain length on physical properties, Ferroelectrics, 181, 319-326 (1996). 

Pfeiffer, M., Beresnev, L. A., Haase, W., Scherowsky, G., Kuehnpast, K., and Jung-bauer, D., Dielectric and electrooptic properties of a switchable ferroelectric liquid crystalline side chain polymer. Mol. Cryst. Liq. Cryst., 214, 125-141 (1992). 

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