Synthesis and properties of chiral azo-liquid crystalline terpolymer containing cyano mesogenic units

A series of side-chain cholesteric polysiloxanes (PQ) were synthesised with poly(methyl--hydrogeno)siloxane, cholesterol (4-allyoxybenzoate) (M1), and 4-hydroxyphenyl-4(allyloxy) phenylpropanoate (M2), 4-allyloxy-4 ‘-cyanobiphenyl (M3). Then azo-containing chiral liquid crystalline polymer (PZ) were synthesised with PQ and 4-(4-hexyloxyphenylazo) benzoic acid (M4) by esterifying catalysed by 4-dimethylaminopyridine which is a new synthetic way. The chemical structures of monomers and polymers were confirmed by conventional spectroscopic methods and test methods for liquid crystal properties. The photo-induced isomerisation of the polymer is investigated by UV–vis spectroscopy. Weight lost temperatures (5%) for all polymers were greater than 298°C. The results showed that the introducing of azo moieties makes the polymer more stable on thermo dynamics. The transition temperatures of the polymers PQ and PZ exhibited some regularity as the change of ingredients of polymers. PQ series showed Grandjean textures and PQ1–PQ5 exhibited blue selective reflection in the visible light region. PZ1–PZ5 also showed Grandjean textures and the texture colour of the polymer turned to red and colourful with green and blue due to increasing contents of azo moiety, and yellow selective reflection in the visible light region were observed. The molecular design introducing shorter and harder part into chiral polymerisation system is favourable to the appearance of selective reflection. All polymers turned out right-handed optical activity due to having the same cholesteric group, the photo-responsive behaviours of the PZ series were also investigated.