Birefringence inversion in liquid crystalline poly(substituted methylene)s bearing side-on mesogens

Abstract

Liquid crystalline poly(substituted methylene)s (PMs) with side-on mesogens exhibit reversible birefringence (Δn) inversion during liquid crystal (LC)-to-LC phase transitions as the temperature increases. The low-temperature LC phase exhibits a positive Δn with the slow axis parallel to the mesogens’ long axis and polymer backbone. Increasing temperature reduces the degree of mesogen alignment, decreasing the magnitude of Δn. The high-temperature LC phase loses mesogen orientation while maintaining the backbone alignment, producing a negative Δn with the slow axis perpendicular to the main-chain axis. These results demonstrate that LC polymers, such as the PMs, can enable the development of optical materials reversibly inversing the sign of Δn by integrating two orientational elements with opposing Δn signs that lose their orders in response to different stimuli.