LIQUID-CRYSTALLINE MAIN-CHAIN POLYMERS WITH A POLY(P-PHENYLENE TEREPHTHALATE) BACKBONE .5. DYNAMIC-MECHANICAL BEHAVIOR OF THE POLYESTER WITH DODECYLOXY SIDE-CHAINS

Tapes of the thermotropic, comb-like, polymer poly(p-phenylene-2,5-did odecyloxyterephthalate) were investigated by dynamic mechanical therma l analysis in tension. This polymer, in which the main chains form lay ers, exhibits three different low-temperature structures, characterize d by the amount of side-chain ordering. The influence of the structure as well as the degree of orientation on the dynamic modulus of films was measured. The results show that the temperature-dependent modulus of oriented films is largely determined by the successive side-chain r elaxations and disorderings. The main differences in modulus between t he structures arise because of the beta relaxation around -35-degrees- C; they level off at higher temperatures on passing the respective sid e-chain disordering transitions.