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

Abstract

Solution-cast films of poly( p-phenylene 2,5-didodecyloxyterephthalate) were characterized by X-ray diffraction, differential scanning calorimetry and mechanical measurements. Three different structures, in which the main chains are arranged in layers separated by the interdigitating side chains, could be distinguished. In the as-cast films these layers 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 is maintained. At room temperature the Young's moduli of the less-ordered phases, termed A and L f, are approximately 15 GPa, which is rather low in comparison with the value of almost 30 GPa found for the third modification, termed B. However, below the β-relaxation at ∼ −20°C the moduli of all three phases are of the same order of magnitude. At −175°C they are in line with the theoretically predicted modulus of 50 GPa.