Chain Thermotropic Liquid-Crystalline Polymers

Main-Chain Thermotropic Liquid-Crystalline Polymers 

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Some particularities of the extraction of ions from an aqueous organic phase, and of the phase catalyzed polyetherification will be summarized. These will represent the fundamentals of our work on the synthesis of some novel classes of functional polymers and sequential copolymers. Examples will be provided for the synthesis of functional polymers containing only cyclic imino ethers or both cyclic imino ethers as well as their own cationic initiator attached to the same polymer backbone ABA triblock copolymers and (AB)n alternating block copolymers and a novel class of main chain thermotropic liquid crystalline polymers containing functional chain ends, i.e., polyethers. 

Three major topics of research which are based on phase transfer catalyzed reactions will be presented with examples. These refer to the synthesis of functional polymers containing functional groups (i.e., cyclic imino ethers) sensitive both to electrophilic and nucleophilic reagents a novel method for the preparation of regular, segmented, ABA triblock and (A-B)n alternating block copolymers, and the development of a novel class of main chain thermotropic liquid-crystalline polymers, i.e., polyethers. 

In the procedures below, methodology is described to facilitate medium scale (ca. 100 g) synthesis of a main-chain thermotropic liquid crystalline polymer containing ethylene glycol units as a flexible spacer between the rigid aromatic units. Two methods are described melt polymerization, and polymerization in a heat-transfer solvent with an inorganic medium (Claytone). For melt polymerization, the material is obtained as an extremely rigid solid, while in the... 

Main-Chain Thermotropic Liquid-Crystalline Polymers... 

X. Jin and T. S. Chung, Thermal decomposition behavior of main-chain thermotropic liquid crystalline polymers, Vectra A-950, B-950, and Xydar SRT-900, Journal of Applied Polymer Science, 73, 2195 (1999). 

Part I Main-Chain Thermotropic Liquid-Crystalline Polymers... i... 

Solution behavior occupies a central position in polymer science. Here we briefly review some recent results for th solution properties of main chain thermotropic liquid crystalline polymers (LCPs) dissolved in liquid crystalline solvents. We concentrate on the distortional properties of such LCPs. 

Figure 1.69 General structure of main-chain (M.C.) and side-chain (S.C.) LCPs. Adapted from T. S. Chung, The recent developments of thermotropic liquid crystalline polymers. Polymer Engineering and Science, 26(13), p. 903. Copyright 1986, Society of Plastics Engineers.

Thermotropic liquid crystalline polymers, like polyesters containing mesogenic units on the main chain, may not be described by the wormlike chain model (cf. Sect. 1.2). The present article does not consider this type of polymers. 

Shibaev, V. P., Moiseenko, V. M., Plate, N. A. Thermotropic liquid crystalline polymers, 3, Comb-like polymers with side chains simulating the smectic type of liquid crystals. Makromol. Chem. 181, 1381 (1980)... 

The rigid rod chains in para-aramids tend to form so-called liquid crystals when they are dissolved in polar solvents or heated to certain temperatures. The polymers showing liquid crystalline behavior in melts are called the thermotropic liquid crystalline polymers, and those showing similar properties in solution are called the lyotropic liquid crystalline polymers. These liquid crystals exist in three distinct phases according to their specific structures (Fig. 12.25). 

Hsieh et al [62] found that for a range of thermotropic liquid crystalline polymers, the greater the free volume measured by PAL the greater the chain mobility at Tg and the higher the value of tan S (damping strength) measured by dynamic mechanical analysis. 

Semiyen, J. A. Ring-Chain Equilibria and the Conformations of Polymer Chains. Vol. 21, pp. 41-75. Sharkey, W. H. Polymerizations Through the Carbon-Sulphur Double Bond. Vol. 17, pp. 73-103. Shibaev, V. P. and Plati, N. A. Thermotropic Liquid-Crystalline Polymers with Mesogenic Side Groups. Vol. 60/bi, pp. 173-252. 

The homopolyestcr of 4-hydroxybcnzoic acid and its copolyestcrs with 6-hydroxy-2-naphthoic acid and with 4,4 -biphenol and tcrephthalic acid are of continuing commercial and academic interest. (1,2) From the applications side, interest stems from the high moduli and high temperature properties of these polymers, while on the fundamental side, interest arises from the main-chain thermotropic liquid crystalline... 

Thermotropic side-chain ionic liquid-crystalline polymers are particularly attractive when the aim is that of merging the liquid-crystalline characteristics of the low molecular weight mesogen side groups with the mechanical properties of the polymeric main chain. It is not surprising, then, that they attracted most of the research efforts in the polymeric ionic liquid crystals field. 

The unique molecular packing of rod-like chains in liquid crystalline polymers (LCP) closely resembles the extended chain structure of highly oriented flexible chain polymers, suggesting that these materials are good candidates for barrier applications. Thermotropic LCP s, first developed in the early 1970 s, have been the object of much interest because of their excellent mechanical properties and ease of product fabrication. Preliminary observations have shown that a commercially available wholly aromatic thermotropic copolyester has gas permeability coefficients that are lower than those of polyacrylonitrile (4.). These results raise some fundamental questions as to the nature of the mechanism for transport of small molecules through a matrix of ordered rigid rod-like chains. 

Thermotropic liquid crystalline polymers containing P-diketonato groups 11 give inter-chain complexation of the diketonato groups with Cu(II) and Ni(II) [27]. ESR indicates that square-planar coordination is present in the case of Cu(II), orientated parallel to the fiber axis. Too high a metal content suppresses the mesogenic properties owing to the insolubility and reduced mobility of the... 

Jackson and Kiitifuss reported a thermotropic liquid crystalline polymer which was a copolyester of poly(ethylene) terephthalate (PET) and parahydroxybenzoic acid (PHB). In this copolyester, PET has a flexible chain conformation while PHB has a stiff, rod-like conformation and the polymer is indicated to be the liquid crystal forming component. Schematically, this copolyester... 

As described earlier, thermotropic, liquid crystalline polymers can be obtained by inserting flexible units in the main chain. As shown in Figure 8, these units can be hydrocarbon ... 

Adduci, L. L.Chapoy, G. Jonsson, J. Kops and B. M. Shinde, Semi-Stiff Chain Aromatic Polyamides New Candidates for Thermotropic Liquid Crystalline Polymers, Polym.Eng.Sci., 21 712 (1981). 

Extended chain crystals represent the most thermodynamically stable state. However, kinetically, it is very difficult. Extended chain crystals can be grown only under extreme conditions in flexible chain polymers, such as high pressure and high temperature [9]. Nevertheless, the polymer chains of most thermotropic liquid crystalline polymers are rigid. It is unlikely for rigid, rod-like molecules to form chain-folded crystallization. Macromolecules in rigid chain polymers may take extended chain crystallization [10]. 

The preparation methods and the novel permselective characteristics of (polymer/LC) composite films have been extensively studied (1-3). Also, various types of (polymer/LC) composite systems have been reported as large area and flexible light-intensity controllable films (4-11). Since thermotropic liquid crystalline polymers (LCPs) with mesogenic side chain groups exhibit both inherent mesomorphic properties of LC and excellent mechanical characteristics of polymeric materials, LCPs... 

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