Main spacer, linked side chain mesogens

Polymers with Side-Chain Mesogens Linked at the Main Chain Spacer... 

With these three different examples it has been demonstrated that the systematics observed for the polymorphism of m-l.c. s is also valid for the side chain polymers, provided that a flexible spacer connects the rigid mesogenic moieties to the polymer main chain. Deviations from this behavior are observed, when the mesogenic moieties are directly linked to the backbone. Under these conditions, normally no liquid crystalline behavior is to be expected, according to the model considerations mentioned in Chap. 2.1. Some examples, however, proved l.c. properties for such systems, which are characterized by two striking properties Very high glass transition temperatures and only smectic structures even in case of short substituents... 

All Liquid Crystal Polymers are characterised by the fact that they contain stiff meso-genic groups, often inserted in flexible chain systems (so called "spacers") and connected to them by linking functional groups the mesogenic unit is inserted either in the main chain or in the side chains or (in exceptional cases) in both. We shall discuss MCLCPs and SCLCPs. A schematic representation of common structures of LCPs is displayed in Fig. 6.14 (Jansen, 1996). An example of a SCLCP with disc-like mesogens is displayed in Fig. 6.15 (Franse et al., 2002, 2004). 

In addition to these main-chain liquid crystalline polymers, there are also side-chain liquid crystalline polymers, where the liquid crystalline nature arises from the presence of rigid straight side-chain units (called the mesogens) chemically linked to an existing polymer backbone either directly or via flexible spacer units. 

Thus, the subject of the review are linear and cyclolinear etement-organic polymers forming a spedfic type of the mesophase state. The structure of the mesoj iases and the formation of liquid crystalline macromolecules, in wiiidi classical mesogens in the main or side chains are linked by flexible polysiloxane or poly-phosphazene spacers are similar to the liquid-crystalline polymers with organic spacers. Structure and properties of these polymers have been reviewed recently and, therefore, will not be considered in our article. 

For example, the interplay between the backbone chain and the mesogenic side chains can make the nematic phase of scLCPs more complex than a normal nematic (cf. Section 4.3). The nature and magnitude of such an interlay may be expected to depend, to a large extent, on the length, stiffness and shape anisotropy of the otherwise weakly interacting spacer group linking the side chains to the main chain. In the... 

Thus, the remoteness of mesogenic groups from the backbone provided by a polymethylene spacer secures them sufficient autonomy from the main chain. On the other hand, the fact that mesogenic groups are chemically linked with the main chain of the macromolecule assists their cooperative interaction. This is why comblike polymers have come to be accepted as convenient matrices for constructing LC polymers. Already a few hundred liquid-crystalline polymers with various mesogenic side groups have been synthesized. 

Polymer (la) in principle has the same chemical constitution as polymer (lb), however, the rigid mesogenic benzoic acid phenyl-ester group is linked to the backbone by the short flexible spacer of only two methylene units. Owing to their chemical constitution strong interactions of the main chain and the mesogenic side groups are to be expected. Actually this polymer exhibits unusual optical properties No typical nematic... 

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