Liquid-crystalline main-chain polymers with a poly(p-phenylene terephthalate) backbone, 9.^† Dynamic mechanical and dielectric behaviour of the polyester with 6-(pentyloxy)hexyloxy side chains

In the liquid-crystalline polymer poly(p-phenylene terephthalate) with dodecyloxy side chains the various possible crystalline structures of the side chain layers determine the mechanical and dielectric behaviour in the solid state. In this investigation the influence of replacement of the methylene unit at the centre of the side chain by an oxygen atom is studied by means of dynamic mechanical and dielectric measurements. It turns out that the oxygen replacement results in an obstruction of crystallization within the side-chain layers, as is clearly manifested by the enhancement of the β-relaxation (attributed to the amorphous side-chain regions) and the nearly complete disappearance of the β^*-relaxation (crystalline side-chain regions).