LCP—See Liquid crystalline polymers

Liquid crystalline polymers (LCPs), 10 374, 517-518 13 370-372. See also Liquid-crystal polyesters (LCPs) Liquid-crystal polymers (LCPs) thermotropic, 13 381-382 Liquid-crystalline thermotropic polyesters, 20 34... 

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. 

Liquid crystalline polymers (LCPs) are best thought of as being a separate, unique class of TPs. Their molecules are stiff, rodlike structures organized in large parallel arrays or domains in both the melted and solid states. These large, ordered domains provide LCPs with characteristics that are unique compared to those of the basic crystalline or amorphous plastics (see Table 2-9) [2]. 

The commercial polymers used in the study are characterized in Table 1. The polypropylenes PP1-PP5 were homopolymers exhibiting different melt viscosities (see Fig. 1) supplied by Neste Chemicals. Liquid-crystalline polymer 1 (LCPl) (Vectra A950 by Hoechst Celanese) is a totally aromatic polyester-type thermotropic main-chain LCP copolymer based on p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA). Liquid-crystalline polymer 2 (LCP2) (Rodrun LC-3000 by Unitika Ltd) is a more flexible thermotropic main-chain LCP copolyester consisting of 60%... 

The zero shear viscosity of flexible linear polymers varies experimentally with and theoretically with [20]. Due to the highly restricted rotational diffusion, the viscosity of TLCPs is much more sensitive to the molecular weight than that of ordinary thermoplastics as discussed in section 3. Doi and Edwards predicted that the viscosity of rod-like polymers in semi-dilute solutions scales with A/ [see Equation (12)] [2]. Such a high power dependence of viscosity on the molecular weight has been experimentally observed both for lyotropic LCPs [14,15] and for TLCPs [16-18]. The experimental values of the exponent range from 4 to 7 depending on the chemical structure, the chain stiffness, and the domain or defect structure of the liquid crystalline solution or melt. The anisotropicity of the liquid seems to have little effect on the exponent. A slightly smaller exponent for the nematic phase than for the isotropic phase (6 in the nematic phase versus 6.5 in the isotropic... 

For an introductory account of LCP s including references to more detailed information, see the review article on "Rheology of Rod-like Polymers in the Liquid Crystalline State" by author, J. Rheology 25, 619 (1981). (The bibliography of this paper is appended for reference. 

Elastomeric LCP networks with the potential to show piezoelectric behavior were described by Zentel and co-workers [109, 110, 125, 773]. More recently, Meier and Finkelmann [774, 775] created piezoelectric cholesteric elastomers and described some of their properties. Polymers [776] and networks [126,777] with nonlinear optical responses were recently synthesized. Some of these polymers are liquid crystalline [776], We see no reason why mesogenic monomers and NLO responsive monomers may not soon be combined to form permanently crosslinked NLO LCP networks. 

The first liquid crystal polymers (LCPs), in which structural moieties known to lead to mesomorphic behavior in small-molecule liquid crystals have been incorporated into the main chain, were reported in early 1980s. The presence of the mesogenic units in the polymer chain enhances the tendency for the material to form the liquid crystalline state, and these polymers also show better thermal stability. Both the nematic and smectic phases can be observed in these materials, (see Fig. 4.12). 

Secondly, we see in Table 7.8 a rare example of a side chain polymer with no spacer that is liquid crystalline (n = 0, m=l). Zhou" uses the term mesogen-jacketed to describe the probable microenvironment around the backbone when spacer lengths to lateral mesogens are short, with close proximity of the centres of gravity of the mesogens and the points of substitution onto the backbone. The polymers are then somewhat reminiscent of the longitudinal ( worm ) LCPs dealt with in Chapter 8. 

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