Mesomorphic properties of side-chain polymers bearing a chiral center at the spacer

Abstract

Using the combined techniques of differential scanning calorimetry (DSC), polarizing microscopy and X-ray diffraction, the mesomorphic properties of copolymers obtained from the hydrosilylation reaction of poly(methylhydrosiloxanes) with a non-mesogenic chiral and a nematic achiral vinylic compounds, were investigated. In this type of polymeric systems, the chiral center forms part of the flexible spacer.
The DSC heating curves for the copolymers exhibited wide mesophase range. The data showed that an increase in the non-mesogenic chiral component in the reaction mixture resulted in a lowering of the glass transition temperature and the clearing temperature of the mesophase. The mesogenic copolymers exhibited the textures indicative of an S_C^* phase. Microscopy investigations showed that these copolymers exhibit the pscudo-homeotropic texture.
The identification of the smectic mesophase was supported by X-ray diffraction study. The x-ray pattern for the unoriented sample of one of the copolymers showed one sharp inner ring corresponding to the lamellar thickness of 25.8Å and a diffused outer ring reflecting the absence ofordering within the layer planes.
Enhancement of the thermal stability of the obtained mesophase was observed when photo-cross-linking reaction was carried out on thin films of the prepared polymers. The observed increase in clearing points of the copolymers irradiated at liquid crystalline state suggests that the distribution of the net points stabilizes the smectic order during the cross-linking reaction. It is also possible that the stabilization may have been due to the increase in the molecular weight associated with the cross-linking reaction.