Side Chain Polymer Liquid Crystals

It has been demonstrated that polymers with mesogens attached as side chains can exhibit liquid crystalline properties, and mueh of the basic knowledge we have concerning side-chain liquid crystal polymers is due to the work of Ringsdorf, Finkelmann, Shibaev, and Plate. The extent to which the mesophases can develop in these systems is influenced by the flexibility of the backbone chain and whether 

Effect of Chain Flexibility on the Transition Temperatures of Side-Chain Liquid Crystal Polymers Having a Common Mesogen 

The polymer chain to which the mesogens are bonded can have different degrees of flexibility, and this can affect both the Tg and the temperature of the liquid crystal to isotropic phase transition Tj. This is illustrated in Table 11.7 for a series of polymers with a constant mesogen imit but a chain flexibility that decreases in the order methacrylate aerylate siloxane. The temperatures of the transitions are seen to decrease in the same order. 

The orientational order in nematie polymers can be deseribed by a parameter S, defined by 

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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... 

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... 

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. 

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... 

Laterally appended side-chain liquid crystal polymers tend to exhibit nematic phases... 

Assume a side chain liquid crystal polymer, consisting of a flexible backbone and mesogenic side groups, is able to form the Sc phase and its glass transition is below the ambient temperature, such a side chain liquid crystal polymer will be expected to show ferroelectricity. The side groups are packed in a way similar to small molecular mass ferroelectric liquid crystals. The backbone is suppressed between layers, occasionally penetrating into them. The conformation of the backbone is discus-like. 

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