Chiral photosensitive side-chain liquid crystalline polymers—synthesis and characterization

The cholesteric polysiloxanes (P series) were obtained by reacting cholesteric monomer and phenolic hydroxyl monomer in different ratios with polysiloxanes. And then the chiral azo-containing polysiloxanes (AP series) were synthesized by esterifying P series members with the acryl acid of azo acid catalyzed by DMAP. The chemical structures and liquid crystal (LC) properties of the monomers and polymers were characterized by use of various experimental techniques such as FTIR, 1 H-NMR, POM, DSC, TGA, XRD and ultraviolet-visible. Experimental results proved that obtained polymers were in accordance with the molecular design. The transition temperatures of the polymers exhibited a decreasing trend as the content of the cholesteric units increased and became higher by introducing the azo mesogenic core. The temperatures at which 5 % weight loss occurred are higher than 280 °C. P 2 –P 6 showed blue Grandjean textures and exhibited selective reflection in the visible light region. AP series also possessed Grandjean textures, and the colors exhibited red shift with increasing content of azo moiety. On the heating cycles, when appropriate mechanical pressure was imposed on the polymers, AP 2 –AP 6 selectively reflect visible light; however, there are no reflection peaks in the UV-Vis spectrum without the stimulation of mechanical pressure. All polymers exhibit left-handed optical activity due to having the same cholesteric group. The optical rotation direction of AP changes from left to right when increasing the UV irradiation time, and the photoresponsive behaviors of AP series are also investigated.