Polymers mesomorphism

The X axis represents the concentration of the mixture of the two polymers (mesomorphic or non mesomorphic). 

A 0-jum polymerized film has been placed between two conductive glass plates. When the polymerization of such a layer is performed under orienting electric fields, the dielectric constant decreases from the high value of the liquid crystal to the classical value for the polymer. Mesomorphic order in the resulting polymer will be investigated by x-ray studies. 

The investigations of polymer mesomorphism have been carried out for a wide variety of polymeric systems and for various types of polymers and copolymers. ... 

In this chapter we have tried to outline the chemical structure that leads to the formation of the various mesophases exhibited by side-chain polymer liquid crystals. Electro-optic phenomena in these systems have then been considered in terms of potential device applications. Since such studies have only been carried out over the last five years or so it is evident that there will be many more applications discovered over the next decade as a better understanding of the composite polymer-mesomorphic properties is attained. 

These differences on the stress-strain behavior of P7MB and PDTMB show the marked influence of the mesomorphic state on the mechanical properties of a polymer. When increasing the drawing temperatures and simultaneously decreasing the strain rate, PDTMB exhibits a behavior nearly elastomeric with relatively low modulus and high draw ratios. On the contrary, P7MB displays the mechanical behavior typical of a semicrystalline polymer. 

Characteristic of the microstructure of PET fibers in their final production form is the occurrence of three types of polymer phases crystalline, mesomorphous, and amorphous. The first phase is the result of crystalline aggregation of PET molecules, the second phase—of mesomorphous or, in other words, paracrys-talline aggregation, the third phase—of amorphous aggregation. The mesomorphous and amorphous phases together form a noncrystalline part of the fiber. 

The quantitative proportion of the mesomorphous phase in PET fibers is strongly diversified and depends on the conditions of fiber manufacture. According to Lindner fl7], it is estimated to be in the range 0.21-0.36. For poorly stretched fibers (below 300% of draw ratio), the mesophase constitutes almost exclusively an ordered part of the polymer in the fiber. With an increase in the draw ratio of the fiber, the proportion of the mesophase in the whole fiber mass increases, mainly at the cost of the amorphous phase. It is assumed that the mesophase constitutes about 0.5 of the amorphous phase mass for poorly stretched fibers and about 1.2 of this mass for highly stretched fibers. 

In this subsection some examples are presented of polymorphic polymers, for which one or more forms are solid mesomorphic, in the sense described in the Sect. 2.1. Let us recall that in this review we will not deal with liquid mesomorphic forms. 

Attard GS, Garnett S, Hickman CC, Imrie CT, Taylor L (1990) Liq Cryst 7 495 Shibaev VP, Lam L (eds) (1994) Liquid crystalline and mesomorphic polymers. Springer, BerUn Heidelberg New York... 

Starkweather H.W., Cocrystallization and polymer miscibility, J. Appl. Polym. Sci., 25, 139, 1980. Seguela R. and Pmd homme J., Affinity of grain deformation in mesomorphic block polymers submitted to simple elongation. Macromolecules, 21, 635, 1988. 

Fig. 18 Components used to form mesomorphic, halogen-bonded polymers...

Poly(epichlorohydrin) (PECH) and poly(2,6 - dimethyl-1,4-phenylene oxide) (PPO) containing pendant mesogenic units separated form the main chain through spacers of zero to ten methylene units were synthesized and characterized in order to test the "spacer concept." Both polymers were modified by phase transfer catalyzed esterifications of the chloromethyl groups (PECH) or the bromobenzyl groups (brominated PPO) with potassium co -(4-oxybiphenyl) alkanoates and potassium u-(4-methoxy-4-oxybiphenyl)-alk.an oates. While PPO required ten methylene units as a spacer and 4,4 -methoxybiphenyl as mesogen to present thermotropic liquid crystalline mesomorphism,... 

Figure 8 Liquid-crystalline polymers in which the mesomorphic sequences occur in the side-chain (middle), in the chain backbone (top), or in both (bottom) ( combination structures).

A number of systems which in polymer literature are normally referred to as mesophases are obtained under kinetic control. Examples are the smectic phase of isotactic polypropylene [18,19], mesomorphic syndiotac-tic polypropylene [20-22], mesomorphic PET [23,24], and other instances where intermediate degrees of order result after quenching polymers from the melt to temperatures often close to Tg. In these cases disorder is plausibly more static than in bundles close to T0 and these phases usually crystallize upon heating to an appropriate temperature in the stable crystal phases. 

Polymers showing crystalline mesomorphic modifications, characterized by chains in disordered conformations, are exceptions to the equivalence principle. Examples of these cases are shown in Section 2.6. 

Mesomorphic forms characterized by conformationally ordered polymer chains packed in lattices with different kinds of lateral disorder have been described for various isotactic and syndiotactic polymers. For instance, for iPP,706 sPP,201 sPS,202 syndiotactic poly(p-methylstyrene) (sPPMS),203 and syndiotactic poly(m -methylstyrene),204 mesomorphic forms have been found. In all of these cases the X-ray fiber diffraction patterns show diffraction confined in well-defined layer lines, indicating order in the conformation of the chains, but broad reflections and diffuse haloes on the equator and on the other layer lines, indicating the presence of disorder in the arrangement of the chain axes as well as the absence of long-range lateral correlations between the chains. 

There are several very important advantages we obtain from this novel class of LC polymers. They can be prepared with well defined chain ends and narrow molecular weight distribution. Therefore, we could provide important information concerning the influence of the nature of the polymer chain ends on their mesomorphic... 

Field-induced change in the orientation of either dichroic dye molecules (the guest) dissolved in a mesophase (the host) or dichroic dye moieties (the guest) of polymers (the host) resulting in changes in the absorption spectrum of a mesomorphic mixture. 

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