LIQUID-CRYSTALLINE MAIN-CHAIN POLYMERS WITH A POLY(P-PHENYLENE TEREPHTHALATE) BACKBONE .4. X-RAY-DIFFRACTION OF THE POLYESTER WITH DODECYLOXY SIDE-CHAINS

A detailed X-ray investigation on oriented fibres and films of poly(p- phenylene 2,5-didodecyloxyterephthalate) revealed that this polymer ca n exist in two stable crystal modifications, A and B, at room temperat ure. Modification B is a highly crystalline classical structure. In mo dification A the side chains do not follow the restrictions imposed by their regular attachment to the main chains; they form clusters betwe en the main chain layers. Upon heating to above the side chain disorde ring temperature T(s) (T(s)(A) almost-equal-to 40-degrees-C, T(s)(B) a lmost-equal-to 100-degrees-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) (almost-equ al-to 170-degrees-C) part of the positional ordering of the main chain s is lost and a mesophase with biaxial ordering exists. This biaxial o rdering is lost at T(i) (almost-equal-to 240-degrees-C) and an isotrop ic melt is formed.