LIQUID-CRYSTALLINE POLYMERS

Liquid crystalline polymers (LCPs) can be divided into two broad categories, according to their molecular architecture: main chain and side chain. In each case the LC phase can be found in an appropriate temperature range, known as its thermotropic characteristic. Liquid crystallinity can be stabilised at lower temperatures in main chain polymers by the addition of solvent to form a lyotropic phase. The most famous and commercially significant lyotropic liquid crystalline polymer is polyparaphenylene terephthalate. This is marketed by DuPont as Kevlar fibre. Most thermotropic systems developed commercially are based on random copolymers of aromatic polyesters. The different units are para-linked, which produces the straight, comparatively rigid molecules required for liquid crystallinity.