The orientation order of liquid‐crystalline polymer, measured by ESR and optical dichroism techniques

ABSTRACT Molecular orientation order and rotation mobility of comb‐shaped liquid crystalline polymer forming nematic and smectic mesophases are characterized by spin probe and dichroism technique in the temperature range 100–420 K. The models describing the mechanism of molecular rotations in different temperature ranges were determined by quantitative numerical simulations of ESR spectra. In the vicinity of the glass transition point of the polymer, where the fast amplitude‐restricted molecular reorientations take place, the quasi‐libration model was found to be adequate for the description of ESR spectra, while the often used Brownian rotational diffusion is appropriate at higher temperatures only. Orientation distribution function of probe molecules was characterized quantitatively by order parameters up to sixth rank for a wide temperature range. The orientation order parameters measured via the spin probe technique are shown to correlate with orientation order parameters measured by optical techniques. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 819–825 The orientation order of a liquid‐crystalline polymer exhibiting a number of nematic and smectic mesophases is measured using a number of paramagnetic and optical molecular probes.