RELAXATION PROCESSES IN THERMOTROPIC POLYDIBENZOATES WITH OXYETHYLENE SPACERS IN THE MAIN-CHAIN

A dynamic mechanical analysis has been performed on three thermotropic polydibenzoates, designated PDEB, PTEB and PTTB, synthesized from p,p'-dibenzoic acid and di-, tri- or tetraethylene glycol, respectively. The isotropization temperature decreases greatly as the length of the spacer increases, and the mesophase of PTTB is not detected at all. Three dynamic mechanical relaxations are found for each polymer in the temperature range from -150 to 100-degrees-C. The ot relaxation corresponds to the glass transition of the polydibenzoates, the beta relaxation is typical of polyesters and the gamma relaxation has its origins in the crankshaft motions of the oxyethylene units in the spacer, i.e. the oxygen atom can cooperate in this movement when substituting for a methylenic unit.