Liquid-crystalline polyesters containing alternating alkylene and oxyalkylene spacers

Three new series of thermotropic polyesters were prepared in which the structural units consisted of two p-oxybenzoyl dyads alternately flanked by a polymethylene segment and an oxyethylene oligomer. In each series the length of the oxyethylene residue was fixed (n = 2, 3 or 4) and the length of the alkylene segment was varied (m = 6-10 and 12). Details of the synthesis and characterization of the polymers are reported. The effect of the parity and length of the oxyethylene and polymethylene segments on the incidence of mesophases and on their thermodynamic parameters is stressed. The substitution of methylene groups by oxygen atoms in the polymethylene spacer of a fourth series of polymer analogues completely inhibited the nematogenicity of the polymers incorporating even powerful mesogens such as the p-oxybenzoyl dyads.