Influence of the spacer on the thermotropic and conformational properties of poly(oxybis(trimethylene) p,p'-bibenzoate) and poly(heptamethylene p,p'-bibenzoate)

The effect of the ether group of the spacer of poly(oxybis(trimethylene) p,p'-bibenzoate) (PDTMB) on the thermotropic behavior of this polyester has been analyzed by comparing the properties of PDTMB with those of poly(heptamethylene p,p'-bibenzoate) (P7MB), the analogue polybibenzoate with an all-methylene spacer. The ability to develop three-dimensional order from the mesophase is greatly diminished by the presence of the oxygen atom. Moreover, P7MB exhibits a monotropic behavior as the crystal, on heating, is transformed directly into the isotropic melt, while PDTMB appears to be a "regular" thermotropic polymer. The oxygen atom, however, seems to have almost no influence on the stability of the mesophase, and both polyesters present similar thermodynamic parameters for the liquid crystalline phase.