Side-chain LCPs polymer backbone

Side-chain LCPs can be prepared by attaching a mesogen pendant to a flexible polymer backbone (18). These materials often have optical properties similar to low molar mass LCs and have generated interest for such applications as non-linear optics, filters and optical storage devices. 

This paper presents summaries of unique new static and dynamic theories for backbone liquid crystalline polymers (LCPs), side-chain LCPs, and combined LCPs [including the first super-strong (SS) LCPs] in multiple smectic-A (SA) LC phases, the nematic (N) phase, and the isotropic (I) liquid phase. These theories are used to predict and explain new results ... 

Ei ft 0, (In t ) — (In O3) - 0, and E2 — Ej - 0. For the particular Cl side-chain LCPs and Cl combined LCPs (including SS LCPs) studied (3-13) with the earlier single-component analogue of this mixture theory, it has been found that the N LC phase and the I liquid phase for these polymers involve the packing of plate-like sections of backbones and side chains thus, (ln 0- ) 0, (ln f ) 0,... 

Side-chain LCPs are, in a way, more subtle than their main-chain counterparts because, thanks to the flexible spacers, the polymer main chain (called backbone) still retains many degrees of freedom. In fact, there is a true balance between the natural disorder of the backbones and the liquid-crystalline order of the rod-like moieties. For instance, in the SmA phase, it was recently demonstrated by SANS that the backbone performs a 2-dimensional random walk between the smectic layers [22]. Therefore, these materials have poor mechanical properties but display a rich variety of mesophases, even at room temperature. This makes them more suitable for applications in displays and electro-optic devices. 

The liquid crystalline material in the LCD is not necessarily a LCP. However, in order to fix the liquid crystalline material conventional polymers are used for embedding and LCP are also used. Side chain LCPs combine the properties of liquid crystals and polymers with flexible main chains. Since the liquid crystal moieties are fixed on the backbone of the main chains of the polymer, this type of liquid crystals may not flow away, as it may be the case in monomeric liquid crystals. 

In main chain LCPs the mesogens are part of the polymer backbone, while side chain LCPs are formed when the mesogens are connected as lateral substituents to the polymer, in most cases via a flexible spacer . Also, combinations of main chain and side chain LCPs are known. 

So how do these common, useful polymers relate to liquid ciystal polymers (LCPs) Well if the alkene monomer (1) is substituted by a moiety conducive to the generation of liquid crystal phases, then the resulting polymer may exhibit liquid crystalline phases (see below). Similarly, if the methyl ester unit in monomer 3 is replaced by a long, rod-like moiety similar to the liquid crystal stractures shown in Chapter 3, then on polymerisation a liquid crystalline methacrylate polymer may result. In each case the mesogenic units are attached to the side of the polymer backbone and such systems are denoted side chain polymers. If either or both of the bifunctional units involved in a condensation polymerisation e.g., 8) are of a mesogenic nature e.g., a biphenyl or terphenyl unit), then a liquid crystalline polymer may result. In this case the mesogenic units are a part of the backbone stmcture and such systems are denoted main chain polymers. 

Collings PJ (1990) Nature s delicate phase of matter. Adam Hilger lOP, Bristol, p 196 Datta A, Chen HH, Baird DG (1993) The effect of compatibilization on blends of polypropylene with a liquid-crystalline polymer. Polymer 34(4) 759-766 Davidson P (1999) Selected topics in X-ray scattering by liquid-crystalline polymers. In Mingos DMP (ed) Liquid crystals II. Springer, Berlin, pp 1-39 Dowell F (1988) New theories for smectic and nematic liquid-crystal polymers backbone LCPs and their mixtures and side-chain LCPs. Mol Cryst Liq Cryst Inc Nonlinear Opt 157 (l) 203-227... 

The double architectures shown in Table 1.1 correspond to LCPs more commonly referred to as combined , indicating that their structures combine the features of main chain and side chain LCPs. Thus mesogenic entities are located both in the side chains and in the polymer backbone, and mesophase microstructures tend to contain mesogens from each of these environments. Ordering that involves main chain components implies a tendency away from the random-coil conformation associated with flexible, non-mesogenic backbones this is possibly why double LCP materials are often crystalline and tend to exhibit at least one smectic mesophase (sometimes several) in their thermal profiles. 

Super-strong (SS) polymers (3-11) are specially-designed combined LCPs in which the side chains of one molecule are designed to interdigitate (pack between) the side chains of neighboring molecules, thus leading to molecular self-reinforcement and enhanced molecular ordering (thus, enhanced mechanical properties) compared to backbone LCPs. 

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