LIQUID-CRYSTALLINE MAIN-CHAIN POLYMERS WITH A POLY(P-PHENYLENE TEREPHTHALATE) BACKBONE .3. DRAWING, STRUCTURE DEVELOPMENT AND ULTIMATE MECHANICAL-PROPERTIES OF FILMS OF THE POLYESTER WITH DODECYLOXY SIDE-CHAINS

Solution-cast films of poly(p-phenylene 2,5-didodecyloxyterephthalate) were characterized by X-ray diffraction, differential scanning calori metry and mechanical measurements. Three different structures, in whic h the main chains are arranged in layers separated by the interdigitat ing side chains, could be distinguished. In the as-cast films these la yers are parallel to the film surface. Upon drawing, the backbones of the chains orient parallel to the drawing direction, while most of the parallel orientation of the layers with respect to the film surface i s maintained. At room temperature the Young's moduli of the less-order ed phases, termed A and L(f), are approximately 15 GPa, which is rathe r low in comparison with the value of almost 30 GPa found for the thir d modification, termed B. However, below the beta-relaxation at approx imately - 20-degrees-C the moduli of all three phases are of the same order of magnitude. At - 175-degrees-C they are in line with the theor etically predicted modulus of 50 GPa.