A SIDE-CHAIN LIQUID-CRYSTAL COPOLYMER SYSTEM WITH MESOGENIC UNITS OF OPPOSITE SENSE COUPLINGS

A side-chain liquid crystal polymer consists of two normally incompatible components, namely the polymer backbone and the mesogenic units. The inherent connectivity of the polymer system which inhibits phase separation leads to some coupling of the long range orientational order of the mesogenic units to the polymer backbone. Such coupling can result in mesogens lying preferentially parallel or perpendicular to the backbone. A series of copolymers has been prepared in which the two homopolymers prepared from the constituent monomers show these two possibilities. In order to assess the competing influences of these two opposing couplings, the phase behaviour is determined using a combination of thermal analysis, optical microscopy and X-ray scattering. It is found that across the composition range either the parallel or perpendicular arrangement is preferred except at a composition of 75/25 mol% at which the system exhibits minimal coupling. At this composition the monomer with the perpendicular coupling is in the majority. Using these observations and the results of mean-field models of the coupling it is shown that the 'hinge' effect is twice as effective as the 'nematic' like interactions between the mesogens and the polymer chains in determining the nature of the coupling.