Longitudinal liquid crystal polymers

Class a, longitudinal liquid crystal polymers, earlier called main-chain polymers. A new name is necessary to distinguish them from the following classes jS and y and the subclasses (S, (R and Al. There are numerous examples of class a. We do not discuss them here in any detail since the entire Chapter 8 by MacDonald is devoted to thermotropic ones, while Chapter 6 by Northolt and Sikkema deals with lyotropic PLCs of the same class. Orientational and conformational order in longitudinal PLCs is discussed by Frangoise Lauprete in Section 3.1.3.1 would only like to note an account of the history of first polyesters in this class and of future perspectives by Jackson. ... 

NMR Studies of Local Dynamics in Longitudinal Liquid Crystal Polymers... 

Preedericksz transition in planar geometry is uniform in the plane of the layer and varies only in the z direction. However, in some exceptional cases, when the splay elastic constant Ki is much larger than the twist elastic constant K2 (e.g., in liquid crystal polymers), a spatially periodic out-of-plane director distortion becomes energetically favourable. The resulting splay-twist (ST) Freedericksz state is manifested in experiments in the form of a longitudinal stripe pattern running parallel to the initial director alignment no x. 

PLCs have also low isothermal compressibilities. Some longitudinal polyesters in the melt phase have compressibility of about 60% of values for non-liquid-crystal polymer melts. 

Brostow Witold, Faitelson Elena, A., Kamensky Mihail, G., Korkhov Vadim, R, Rodin Yuriy, P. (1999). Orientation of a Longitudinal Polymer Liquid Crystal in a Constant Magnetic Field. Po/yw, 40(6), 1441-1449. 

Figure 3.1 Schematic designs of (a) longitudinal and (b) comb-like polymer liquid crystals with non-covalent bonds.

MORPHOLOGY OF THERMOTROPIC LONGITUDINAL POLYMER LIQUID CRYSTALS... 

Longitudinal polymer liquid crystal + engineering polymer blends miscibility and crystallization phenomena... 

Figure 14.30 Temperature dependence of the relative absorption of the longitudinal wave at 2 MHz parallel (a ) and perpendicular (a ) to the axis of the mesogenic units of a side chain polymer liquid crystal with a polymethylsiloxane backbone. (Adapted from [17] by permission of Israel Institute of Technology.)...

We recall that the first liquid crystals, which were monomer LCs (MLCs), were discovered by Friedrich Reinitzer in 1888 [23] while the first book about them appeared 20 years later [24]. While much has been done in the last century, both MLCs and PLCs remain fascinating object to study and to apply. We have seen several results of MD simulations of PLCs. A tacit assumption was made above all along the simulated PLCs were all longitudinal, that is with LC sequences in the main chain and oriented along the chain backbone. Various other classes of PLCs have been synthesized by chemists [18,25,26]. These include orthogonal, with the LC sequences also in the backbone but perpendicular to it. There exist as well various kinds of combs, and even polymers with three-dimensional LC units. MD simulations should be able to elucidate mechanical behavior of such PLCs as well. This is particularly noteworthy since the promise made in section 15.1 to provide simulation results unobtainable from experiments appears to have been kept. 

Classify polymer liquid crystals in fuiKtion of their chemical shuctures. Compare viscosities of longitudinal and orthogonal polymer liquid crystals. 

In the polymerization of the monomers, the mixture is in a liquid crystal phase. The polymerization environment is anisotropic due to the aligning effect of the liquid crystal on the monomer and the anisotropic diffusion of the monomer in the liquid crystal. After the monomers are polymerized, they phase separate from the liquid crystals to form anisotropic fiber-like polymer networks which mimic the structure of the liquid crystal during the polymerization. The polymer networks consist of cylindrical shape fibers with submicron lateral diameter and hundreds of microns in longitudinal length. The inter-distance between the fibers is typically a few microns. 

The other stationary periodic pattern has been observed in polymer lyotropic liquid crystals [78]. The smallness of the ratio K-iilK 1 of a poly-g-benzylglutamate solution results in a structure in which the period of the longitudinal domains is of the same order of magnitude as the cell thickness. Due to the high viscosity of the material (7i = 34 P) the time for domain formation exceeds 2 h. If the director was initial-... 

Brostow W (1992) An introduction to liquid crystallinity (Liquid crystalline polymers from structures to applications). Elsevier Applied Science, New York Brostow W, D Souza NA, Kubat J, Maksimov R (1999) Creep and stress relaxation in a longitudinal polymer liquid crystal prediction of the temperature shift factor. J Chem Phys 110 9706-9712... 

If the spacer is positioned at the end of the longitudinal axis of the mesogen, it is called end-on fixation. If the spacer is located at the side of the mesogen, it is called side-on fixation [50,51]. The nature and the size of the flexible spacer influence both liquid crystalline phase transition temperature and orientation in the polymer liquid crystal [45,52]. The spacers are usually composed of methylene... 

Brostow W, Hess M, Lopez BL, Sterzynski T. Blends of a longitudinal polymer liquid crystal with polycarbonate relation of the phase diagram to mechanical properties. Polymer 1996 37 1551-60. 

Simon GP. Longitudinal polymer liquid crystal+engineering polymer blends miscibility and crystallization phenomena. In Brostow W, editor. Mechanical and thermophysical properties of polymer liquid crystals. London Chapman and Hall 1998. p. 172-213. [Chapter 7]. 

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