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

摘要

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 degrees 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 H-1 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 similar to -45 degrees C (neat PBD) to similar to 20 degrees C (R-e similar to 0.5). LC transition starts at R-e similar to 0.27 (the transition temperature T-m similar to 27 degrees C). With increasing R-e temperature T-m increases and for R-e similar to 0.5 reaches the value T-m similar to 74 degrees 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. (c) 2006 Elsevier Ltd. All rights reserved.