LIQUID-CRYSTALLINE MAIN-CHAIN POLYMERS WITH A POLY(P-PHENYLENE TEREPHTHALATE) BACKBONE .6. DIELECTRIC RELAXATIONS IN THE POLYESTER WITH DODECYLOXY SIDE-CHAINS

Dielectric measurements on three dodecyloxy-substituted poly(p-phenyle ne terephthalate)s are presented and compared with dynamic mechanical measurements reported earlier. The results are interpreted on the basi s of a molecular laminate model for the structural arrangement, i.e. m ain-chain layers separated by partially ordered side chains. Most of t he observed relaxations are assumed to originate from side-chain motio ns. The low-temperature gamma relaxation around -160-degrees-C is ascr ibed to local MotiOns Of the CH2 units in the side chains. The beta re laxation around -35-degrees-C involves a cooperative motion of the amo rphous parts of the side chains, while the beta relaxation just above room temperature is supposed to occur mainly in the crystalline parts of the side chains. Although some main-chain motions may already be i nvolved in the relaxations at lower temperatures, they fully account f or the alpha relaxation observed around 120-degrees-C.