Liquid crystalline main chain polymers with a poly( p-phenylene terephthalate) backbone: 4. X-ray diffraction of the polyester with dodecyloxy side chains

Abstract

A detailed X-ray investigation on oriented fibres and films of poly( p-phenylene 2,5-didodecyloxy-terephthalate) revealed that this polymer can exist in two stable crystal modifications, A and B, at room temperature. Modification B is a highly crystalline classical structure. In modification A the side chains do not follow the restrictions imposed by their regular attachment to the main chains; they form clusters between the main chain layers. Upon heating to above the side chain disordering temperature T s ( T s(A)≈40°C, T s(B)≈100°C) these modifications transfer to the less ordered structure A′, in which the side chains are disordered but the position of the main chains, relative to each other, remains strongly correlated. Above the main chain melting temperature T m (≈170°C) part of the positional ordering of the main chains is lost and a mesophase with biaxial ordering exists. This biaxial ordering is lost at T i (≈240°C) and an isotropic melt is formed.