Mesogenic moiety, liquid crystalline order

The structure of the mesogenic moiety appears to exert a strong influence on the nature of liquid crystalline order developed in a polymer. 

SCLCPs combine liquid crystalline properties and polymeric behavior in one material. If the mesogenic unit is fixed directly to the polymer main chain, the motion of the liquid crystalline side chain is coupled with the motion of the polymer backbone, preventing the formation of a LC mesophase. Therefore, Finkelmann and Ringsdorf proposed that the introduction of a flexible spacer between the main chain and the mesogenic unit would decouple their motions, allowing the mesogenic moiety to build up an orientational order [29,30]. 

For commercial TLCPs having their mesogenic moieties contained within the main chain of the polymer, this structure is often nematic. Nematic order in the liquid crystalline phase is shown schematically in Figure 3. The nematic phase is the LCP phase of lowest order, consisting of aggregates of rod-like molecules. Within each aggregate, or domain, the molecules have a distribution about a common axis, denoted by n.. No order exists, however. 

The liquid crystalline state can be systematically introduced by rigid anisometric building blocks or by amphiphilic moieties. According to their chemical constitution and basically following the same systematic as known from low-molar-mass liquid crystals, all types of LC phase structure are accessible. Additional aspects to be considered arise from modification of the state of order due to the decreased specific volume of the macromolecules (compared to that of the monomers) and the reduced translational and rotational mobility of the mesogenic units due to their linkage within the macromolecule. 

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