Linking groups azoxy

Examples of cyclic units are 1,4-phenylene, 2,6-naphthalene and fr s-1,4-cyclohexylene rings. The linking group connects the cyclic units on each side to give the chain a linear character. The preferred confirmation is planar (linear). A number of different groups fulfil these requirements direct bond, ester, imino, azo, azoxy, and methylol groups (semiflexible). 

The azo group may be oxidized further, usually with a peracid such as 3-chloroper-benzoic acid to give azoxy linked materials examples include compounds 14-16 which are shown below [51, 54, 55], but only compounds 14 and 16 show chiral nematic phases. 

Structurally similar polymers with azo links, Polymers 9 and 10, formed no meso-phases when the rigid aromatic unit contained terminal carbonyl groups, but these formed nematic mesophases when the ester link was reversed The transition temperatures of the azo and azoxy polymers with the same spacer were quite close to each other. Substitution of methyl groups on the phenylene rings of these polymers reduced melting temperatures without adversely affecting nematic mesophase stability... 

Another type of unsaturated mesogenic structure, which is based on a structure in between an azo- and vinylene-type, is that in which a Schiff base unit links two phenylene groups. This unit is similar in geometry to the three previous mesogenic units, the azo, azoxy and stilbene groups The only reported example of this structure, however, was Polymer 8 with a decamethylene spacer, and it was quite similar in properties to the polymers just discussed. It also possessed a smectic phase, and the mesogenic unit had terminal carboxy groups. 

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