Liquid crystalline polymers XI. Main chain thermotropic poly (arylidene–ether)s containing 4-methyl-cyclohexanone moiety linked with polymethylene spacers

A new homologous series of thermotropic liquid crystalline (LC) poly(arylidene−ether)s based on 4-methyl cyclohexanone moiety 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 the 4-methyl-cyclohexanone monomer. A model compound was synthesised from the monomer with benzaldehyde and characterised by elemental and spectral analyses. The inherent viscosities of the resulting polymers were in the range of 0.02−0.36 dI/g. All the poly(arylidene−ether)s were insoluble in common organic solvents and partially soluble in halogenated solvents. The mesomorphic properties of these polymers were studied as a function of the diphenoxyalkane spacer length. Their thermotropic LC 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 thermogravimetric analyses 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 selected examples were tested by scanning electron microscopy.