Effect of mesogenic crosslinking units on the mesomorphic phases of cholesteric liquid crystalline polymers

A series of cyclosiloxane-based cholesteric liquid crystalline polymers were synthesized from cholest-5-en-3-ol (3 beta)-4-(2-propenyloxy)benzoate and a nematic crosslinking monomer biphenyl-4,4'-diol bis[4-(2-propenyloxy)-benzoate], containing mesogenic crosslinking contents among 0-7.8 wt %. Swelling experiments of the elastomers were employed to determine the effective crosslink density (M-c). With increase of mesogenic crosslinking component in the polymers, the isotropic temperature decreases, but both the temperature of glass transition and melting point change irregularly. All the polymers have high thermal stability and percentage weight loss occurred at 460 degrees C decreases with increase of crosslinking units. The intensity of X-ray diffraction peak at 2 theta approximate to 17 degrees decreases with increase of mesogenic crosslinking units, suggesting that the order between two neighbor liquid crystalline molecules disturbed by the mesogenic crosslinking agents. The maximum reflection bands shift slightly to long wavelength and become broad, indicating that the helical structure is partially disrupted because of both the constraint of chemical crosslinking agents and the different mesogenic units. (c) 2007 Wiley Periodicals, Inc.