Thermotropic liquid crystalline polymers—20. Study by i.r.-dichroism spectroscopy of an oriented state of comb-like liquid-crystalline polymers with cyanobiphenyl mesogenic groups

Abstract

The peculiarities of orientation of liquid crystalline (LC) comb-like polymers by action of a shear stress were studied by i.r.-spectroscopy. It has been shown that the type of orientation depends on the average degree of polymerization ( P w ). The long axes of mesogenic groups are oriented along the shear direction at P w < 100 and they are normal to this orientation at P w > 100 . The degree of orientation of mesogenic group (S M ∗) and spacer (S A ∗) was estimated over a wide temperature range. In the LC state of polymers, the S M ∗ values (0.4–0.5) exceed the S A ∗ values (0.1–0.3). To explain this difference, the conformation state of the spacer was considered. For polyacrylate samples with 11 methylene groups in the spacer, the content of gauche isomers in the S A-mesophase is around 25%. At the S A-S C transition, the content gauche of isomers is decreased.