Main-chain LCPs temperatures

Both thermotropic and lyotropic liquid crystal polymers exhibit characteristic features with regard to their microstructureJ Anisometrical monomers such as rods or discs are connected to chains in an appropiate manner. These anisometrical monomers are considered to be the mesogens and may be part of main chain LCP, side chain LCP, or of both types together (Fig. 6). Between the mesogens are located flexible spacers of non-mesogenic character. Sufficient flexibility is a prerequisite for liquid crystal formation, with an increase in either temperature or solvent concentration. 

To obtain a more quantitative picture of the temperature dependence of tr and R IR, specimens of TPBIO were dissolved in a proprietary mixture of low-molar-mass nematics, designated E5, which has a broad nematic temperature range [Chiang et al., 2000]. Experimental results for two TPBIO specimens having DP= 18 and 63 are shown in Eigure 1.10. Eirst, the temperature dependence of R and R may be considered in the context of pertinent statistical theories. An analysis by Halperin and William [1992] of the conformation of main-chain LCPs using an Ising chain model led to the conclusion that the chain dimensions, and R , each exhibit exponential temperature dependence ... 

One typical example of model LCP is PSHQ9, poly[(phenylsulfonyl)-p-phenylene nonanemethylene bis(4-oxybenzoate)] [54], whose chemical structure is depicted in Figure 11.2. This is a main-chain LCP, which has a glass transition temperature Tg of 84 ° C, and a nematic-to-isotropic (N-I) transition temperature Tm of 162 °C. This polymer has only nematic phase at temperatures between and Tni-... 

Where, AH is the difference in enthalpy between the isotropic melts and the anisotropic from of LCPs and AS is the corresponding entropy difference. Thus, T could be reduced by decreasing AH or by increasing AS, or both. The enthalpy is mainly controlled by interchain separation between adjacent LCP chains. An effective approach of decreasing AH is to insert modifying units randomly along the chain. This leads to the formation of random copolymer in which the crystallinity is dismpted (Utracki and Favis 1989 National Materials Advisory Board 1990 Bates 1991 Rudko 2002 Brehmer and de Jeu 2012 Dowell 1988). Considerable efforts have been devoted to reduce the transition temperature of main chain LCPs in order to reach more favorable conditions for industrial processing. 

A great number of initiators and monomers are now available, allowing almost perfect control over most of the important parameters of LCPs main chain stiffness tacticity glass transition temperatures processabiUty from solution or melt mesogen density along the main chain combination with... 

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. 

Introduction of Lateral Groups. Lateral groups have been introduced to lower the melting points of LCPs. Grafting bulky side groups onto the polymer main chain influences the melting temperature in several ways. It effectively... 

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