Preparation, MCLCP

In contrast to ROMP, ADMET offers the possibility of synthesizing both side-chain and main-chain liquid crystalline polymers. The scope and limitations of ADMET are discussed in detail by Wagener et al. in this issue. We herein focus on a few contributions that used step growth polymerization methods to prepare MCLCPs and SCLCPs. 

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... 

The same group reported on the synthesis and characterization of all-hydrocarbon MCLCPs, poly-(XXXX), and their hydrogenated derivatives poly-(XXXXI), based on 4,4 -bis(a-co-alkenyl)-l,r-biphenyl derivatives, see Fig. 23. Monomers with different a-co-alkenyl chain lengths were used to prepare not only the corresponding homopolymers but also statistical copolymers. Crystallinity, thermal transition properties and LC properties were studied. 

Closing this section, a new metathesis-based method for the preparation of strictly alternating copolymers should be mentioned. Alternating diene metathesis polycondensation (ALTMET) was used to prepare a MCLCP consisting of an alternating architecture of a calamitic (linear rod-like core) and a banana-shaped (bend-shape core) mesogen (Fig. 24). 

MCLCPs prepared by ADMET and ALTMET have recently gained much attention. In particular, ALTMET allows the synthesis of perfectly alternating copolymers, opening new possibilities for the design of materials with specific properties. 

Preparation of Main Chain Liquid Crystalline Polymers (MCLCPs)... 

Semiflexible MCLCPs were prepared following two basic conceptual procedures. The first one (melt transesterification) involves the chemical modification of pre-... 

Preparation of Main Chain Liquid Crystalline Polymers (MCLCPs) Table 8. Representation of some typical structures of polyesters and copolyesters. 

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). 

The synthesis of thermotropic polyurethanes, polyethers and aromatic polyazomethines has been reported by other researchers, but at present research on MCLCPs of the type described in this section is concentrated in academia and there has as yet been no major industrial exploitation. Block copolymers of polyarylsulphones and ketones " " are currently exciting interest in a number of laboratories. These have been prepared by synthesizing polyaryl sulphones or ketones with phenolic functionality, acetylating the end groups, and treating these functionalized blocks like a diphenol in a conventional LCP polymerization process. 

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