Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Combined LC-polymers possess the structural properties of both LC main chain and LC side chain polymers. Beneath this structural speciality, their broad LC-phases and their polymorphism (different smectic phases and one nematic phase as a function of temperature) make them interesting. Crucial to an understanding of them is the fact that main chain and side chain mesogens orient parallel to each other and interact cooperatively to form the LC-phase. Due to this synergism the temperature range of the LC-phase is much broader than that of the corresponding LC main chain and LC side chain polymers. This interplay of main chain and side chain mesogens allows structures to be designed with preferably nematic or smectic phases. Whenever both types of mesogens can arrange in the same height, preferably smectic phases are formed. If this is not possible, the nematic phase dominates.The incorporation of chiral groups allows cholesteric and chiral smectic C* phases to be prepared. For the latter, ferroelectric modes have been observed dielectrically. By crosslinking of combined LC-polymers, combined LC-elastomers can be prepared, in which the LC-phases are nearly unchanged. These elastomers allow a mechanical orientation of the LC-phases and, in particular, an untwisting of the helical superstructure of cholesteric and chiral smectic C* phases. In the latter case ferroelectric monodomains are obtained. The piezoeffect - to be expected - for LC-elastomers with chiral smectic C* phases was first demonstrated for this class of polymers.
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