Side-chain liquid crystals

In general terms, high molar mass liquid crystals are classified according to the location of the mesogenic unit in the polymer. Thus, they are either incorporated into the main chain (main-chain liquid crystal polymers - MCLCP Fig. 5A) or they are pendant from the main chain (side-chain liquid crystal polymers - SCLCP Fig. 5B). 

Fig. 5 Schematic representation of the molecular arrangement in A main-chain and B side-chain liquid crystal polymers...

C. B. McArdle, Side Chain Liquid Crystal Polymers, Blackie and Son, Glasgow, 1989. 

Fig. 2-21 Main-chain and side-chain liquid crystal polymers.

McArdle, C. B. In Side Chain Liquid Crystal Polymers McArdle, C. B., ed.. Chapman and Hall New York, 1989, p. 357. 

Figure 2. Schematic structure of side chain liquid crystal polymers with dichroic dyes (imparting nonlinear optical properties) and mesogenic side groups.

McArdle CB, "Side Chain Liquid Crystal Polymers", Blackie, Glasgow, 1989. 

Gray GW (1989) In McArdle CB (ed) Side chain liquid crystal polymers. Blackie, London... 

Percec, V., Pugh, C. in Side Chain Liquid Crystals , McArdle, C. B. Ed., Blackie, Glasgow, 1989. 

Phenylacetylene derivatives, (V), were prepared by Tang [2] and converted into the corresponding polyacetylenes, (VI), as illustrated below, containing a side-chain liquid crystal molecular architecture of backbone + spacer + mesogenic group. These products were subsequently used in electronic and mechanical applications. 

The living ROMP reactions of norbomene and norbomene derivatives have been used to make a variety of polymers possessing unusual properties. Copolymerization of selected fimctionalized norbomenes with norbomene has been used to synthesize star polymers and side-chain liquid crystal polymers. This chemistry has also resulted in the preparation of phase separated block copolymers that contain uniform sized metal or semiconductor nanoparticles. The... 

Shibaev, V. P. Some new physico-chemical aspects of side-chain liquid crystal polymers.. Vloi. Cryst. Liq. Cryst. 243, 201 (1994). 

The concept of a side chain liquid crystal polymer has been demonstrated in a number of laboratories and is well documented in the literature (J ). Most of the side chain liquid crystalline polymers reported to date contain polysiloxane, polyacrylate or polymethacrylate main chains. More recent studies on the effect of backbone flexibility now include the use of flexible poly(ethylene oxide) or more rigid poly( a-chloroacrylate) chains. 

Polyphosphazenes represent a new approach to the design and synthesis of side-chain liquid crystal polymers. Polyphosphazenes are inorganic main-chain polymers consisting of alternating phosphorus-nitrogen atoms in the main chain with two substituents attached to each phosphorus atom. The top of Figure 1 shows the general structure for a side chain liquid crystal polymer a polymer... 

The two-step synthesis process shown in Figure 2 affords several possibilities for preparing new side-chain liquid crystal polymers. The polymerization process allows one to vary the molecular weight and molecular weight distribution (MWD), and potentially change the properties of the liquid crystalline state. Most of the polyphosphazenes reported in the literature, including the examples in this paper, are derived from the bulk uncatalyzed process this... 

For the synthesis of side chain liquid crystal polyphosphazenes, the most important examples in Figure 2 are the alkoxy- and aryloxy-polymers. Mesophase behavior has been noted with simple side chains, such as trifluoroethoxy and aryloxy side chains (9). This mesophase behavior is not conventional liquid crystal order, but polymers which exist in a conformationally disordered state (10). 

Figure 3. Side-chain liquid crystal polyphosphazenes.

Part of the rationale for investigating liquid crystal polyphosphazenes is for nonlinear optical (NLO) applications. In general, for NLO activity, polymers must either contain noncentrosymmetric side chains (eg., side-chain liquid crystal polymers) or highly delocalized (conjugated) backbones (16). Alternatively, polymers can be doped with low molar mass compounds to obtain NLO activity. 

At the present time, only a few side-chain liquid crystal polyphosphazenes have been synthesized and investigated. Opportunities exist to prepare a wide variety of side-chain liquid crystalline polyphosphazenes, based on the polymerization-substitution process outlined in Figure 2. Alternative approaches, such as side chain modification of polyphosphazenes prepared by the thermal decomposition of N-silylphosphoranimines (19), may provide even further options for preparing liquid crystal polyphosphazenes. 

S. Yitzchaik, J. Ratner, F. Buchholtz, and V Krongauz, Photochromism of side-chain liquid crystal polymers containing spironaphthoxazines, Liq. Cryst. 8, 677-686 (1990). 

A H-NMR study of the dynamics of the phenyl ring of a side-chain liquid crystal polymer has been carried out. The rotation of the phenyl ring about its paru-axis has been attributed to the relaxation process and a Gaussian distribution of the activation energy points to a dynamic heterogeneity of the... 

The catalyst, hydrogen hexachloroplatinate IV) hydrate, (H2PtCl6) may be used in the hydrosilylation reaction. If this catalyst is used then the reaction mixture must be left stirring at 60-70X overnight. Sometimes a trace amount of colloidal platinum may be present in the side-chain liquid crystal cyclic siloxane tetramer. This can be removed by adding a small amount of triphenylphosphine (0.1 g) at step 11. 

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