ABSTRACT
Liquid-crystalline (LC) dendrimers may be obtained by introducing
mesogenic elements, similar to those described before (see Figs.
2.2, 2.3, and 2.5) into the dendrimer structure. Also in polymer
liquid crystals, mesogenic units are included into the polymeric
structure leading to partially ordered phases. In those systems,
the rigid anisometric mesogenic units (e.g., calamitic or discotic)
play the essential role on the ordering of the mesophases and the
linking flexible chains remain essentially disordered, inducing some
fluidity to the system (see Fig. 3.1). In main-chain LC polymers
(see Fig. 3.1a) the mesogenic units are included sequentially into
the polymer chain (meaning that the rigid units “interrupt” the
flexible polymeric chain). In side-chain LC polymers, the mesogenic
units are connected laterally with respect to the flexible chain
(see Fig. 3.1b,c). In both cases (main chain and side chain,
respectively), the rigid elements may be connected to the polymer
chain either terminally (“end-on” LC polymers) or laterally (“side-
on” LC polymers) using a convenient spacer, for instance, an alkyl
chain or other flexible molecular segment. Figures 3.1b and 3.1c
represent schematically these two cases, respectively. Figure 3.1d-f
shows schematically some possible arrangements of polymeric
chains and rigid mesogenic units corresponding to nematic, smectic,
and columnar phases of LC polymers.
