Combined SCLCP

Liquid crystallinity can be attained in polymers of various polymer architectures, allowing the chemist to combine properties of macromolecules with the anisotropic properties of LC-phases. Mesogenic imits can be introduced into a polymer chain in different ways, as outhned in Fig. 1. For thermotropic LC systems, the LC-active units can be connected directly to each other in a condensation-type polymer to form the main chain ( main chain liquid crystalline polymers , MCLCPs) or they can be attached to the main chain as side chains ( side chain liquid crystalline polymers , SCLCPs). Calamitic (rod-Uke) as well as discotic mesogens have successfully been incorporated into polymers. Lyotropic LC-systems can also be formed by macromolecides. Amphiphihc block copolymers show this behavior when they have well-defined block structures with narrow molecular weight distributions. 

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]. 

A block copolymer consisting of a SCLCP-block of monomer XXVII with a laterally-attached mesogenic unit, and butyl-acrylate, was synthesized using a combination of ROMP and atom transfer radical polymerization (ATRP) (Fig. 16) [81]. 

Jung-Ii Jin et al. prepared a series of ester-based MCLCPs and realized a combination of MCLCP and SCLCP by copolymerizing the monomers XXXVIII and XXXIX shown in Fig. 22. The Grubbs catalyst 6 was used for this... 

A great maity SCLCPs have been synthesised because of the combination of the vast number of mesogenic core nnits available from stmctuie-property relationship evaluation of low molar mass liquid crystals and the maity different backbone (BB) types possible e.g., siloxanes, acrylates, methacrylates, ethylenes, epoxides). Additionally, as shown in Figure 5.4, homopolymers (5.4a), SC copolymers (5.4b), BB copolymers (5.4c), and SC/BB copolymers (5.4d) considerably extend the scope of known and potential liquid crystal polymers. 

LCPs combine the mechanical properties of polymers with the order of LCs. The low molar mass mesogenic units, which form a LC phase, consist of a rigid core. If this core is extended, so-called main chain liquid crystalline polymers (MCLCPs) are obtained. A second method to obtain LCPs is to connect low molecular weight LC (LMWLC) units via flexible spacers. This approach allows the preparation of side chain liquid crystalline polymers (SCLCPs) (Box 1). 

There are different polymer structures that exhibit LC phases. The extension of the mesogen s rigid aromatic core leads to main chain polper systems. Other approaches are based on the spacer concept. Here rigid cores that are common in LMWLCs are decoupled by flexible alkyl chains. The mesogenic units can be placed either in the main or in the side chain. Also combined MCLCP/SCLCPs have been prepared (figure 3). 

Traditionally, two major classes of thermotropic liquid crystalline polymers have been identified the so called main chain (longitudinal) and side chain (comb) types (MCLCPs and SCLCPs, respectively) (Fig. 2.5). More recently other variants have appeared these are combined LCPs which are hybrid between MCLCPs and SCLCPs, and the rigid rod types described by Watanabe et A great wealth of literature already exists in the form of unified texts and reviews which detail both the major classes of LCPs. Bibliographic data have been compiled" and reviews more or less specific to main chain or comb " polymer systems have appeared. We shall be concerned here only with main chain and side chain LCPs. 

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