VISCOELASTIC RELAXATIONS IN THERMOTROPIC POLYBIBENZOATES

The dynamic mechanical relaxations of two thermotropic polybibenzoates containing the biphenyl group in the main chain have been determined in the temperature range from -150 to 130-degrees-C, at several frequencies. The two polyesters are poly(heptamethylene p,p'-bibenzoate) (P7MB) and poly(oxyditrimethylene p,p'-bibenzoate) (PDTMB). These two polymers differ only in the change of the central methylene in the spacer of P7MB by an oxygen atom in PDTMB. Both polymers show three viscoelastic relaxations and the more remarkable difference is found in the relaxation occurring at higher temperature, considered as the glass transition of the mesophase. This transition appears at a temperature 26-degrees-C lower in the case of PDTMB, due to the higher flexibility introduced by the central ether group.