Liquid crystalline polymers XIV. Main chain thermotropic copoly(arylidene-ether)s based on 4-methyl-cyclohexanone and 4-tertiary-butyl-cyclohexanone moieties linked with polymethylene spacers

A new interesting class of thermotropic liquid crystalline copoly(arylidene-ether)s based on cyclohexanone derivative moieties was synthesised by solution polycondensation of 4,4′- diformyl-α,ω-diphenoxyalkanes (Ia−f) or 4,4′- diformyl-2,2′- dimethoxy-α,ω-diphenoxyalkanes (IIa−f) with methyl-cyclohexanone and 4-tertiary-butyl-cyclohexanone monomers. A model compound III was synthesised from X with benzaldehyde and characterised by elemental and spectral analyses. The inherent viscosities of the resulting polymers were in the range 0.23−0.91 dL/g. All the copoly(arylidene-ether)s were insoluble in common organic solvents but partially soluble in halogenated solvents. The mesomorphic properties of these polymers were studied as a function of the diphenoxyalkane space length. Their thermotropic liquid crystalline properties were examined by differential scanning calorimetry (DSC) and optical polarising microscopy and it was demonstrated that the resulting polymers form nematic mesophases over wide temperature ranges. The thermal properties of those polymers were evaluated by thermogravimetric analysis and DSC measurements and correlated to their structural units. X-ray analysis showed that polymers have some degree of crystallinity in the region 2θ = 5−60°. In addition, the morphological properties of the selected examples were tested by scanning electron microscopy (SEM).