Dynamic mechanical and thermal behavior of liquid-crystalline polybutadiene-diols with mesogenic groups in side chains

Abstract

Liquid-crystalline polybutadiene-diols (LCPBDs) with the comb-like architecture were synthesized by reaction of a LC thiol with the double bonds of telechelic HO-terminated polybutadiene (PBD). LCPBDs with various initial molar ratios of thiol to double bonds of PBD, R 0, in the range from 0.15 to 1, were prepared by the radical reaction at temperature 60 °C for 48 h. The experimentally obtained degree of modification, R e, after the reaction and purification, was determined from elemental analysis – from the amount of sulphur bounded in LCPBDs, GPC and from 1H NMR spectra. The physical properties were investigated by differential scanning calorimetry and dynamic mechanical spectroscopy. With increasing R e ratio the glass transition temperature of LCPBDs, T g, increases from ∼ − 45 °C (neat PBD) to ∼20 °C ( R e ∼ 0.5). LC transition starts at R e ∼ 0.27 (the transition temperature T m ∼ 27 °C). With increasing R e temperature T m increases and for R e ∼ 0.5 reaches the value T m ∼ 74 °C; at the same time also the change in enthalpy at LC transition increases. The LC transition could be detected also by the dynamic mechanical spectroscopy; especially shape and position of mechanical functions on frequency and free volume parameters strongly depend on degree of modification.