X-ray investigations of linear and cross-linked liquid-crystalline main chain and combined polymers

Abstract

X-ray measurements on liquid-crystalline main chain polymers and on combined polymers (polymers with the mesogenic groups in the main chain as well as in the side groups) before and after cross-linking allow the identification of the different liquid-crystalline phases. Smectic A, smectic B and probably smectic C phases are found at higher temperatures. The fibre pattern of the oriented combined polymers are analogous to the fibre pattern of the liquid-crystalline main chain polymers. The comparison implies that the mesogenic groups in main chains and side groups are oriented parallel to each other to form the liquid-crystalline phase. No hint of a microscopic bidirectional orientation is observed. Two different types of orientation were observed in the polymers on drawing, depending on the molecular weight (non-cross-linked polymers) or the elongation (cross-linked polymers). In lower molecular weight polymers the smectic layers are oriented parallel to the fibre axis on drawing. For higher molecular weight polymers and for the cross-linked polymers at higher elongation the smectic layers are oriented perpendicular to the fibre axis and the polymer chains are oriented preferentially parallel to the fibre axis. These two orientations result from a competition between the orientational tendencies of the smectic layers and of the polymer chains.