EFFECT OF MESOPHASE ORDER AND MOLECULAR-WEIGHT ON THE DYNAMICS OF NEMATIC AND SMECTIC SIDE-GROUP LIQUID-CRYSTALLINE POLYMERS

The dynamic moduli of side-group liquid-crystalline polymers (SG-LCPs) having methacrylate backbone, hexamethylene spacer, and phenyl benzoate mesogens are characterized as a function of molecular weight in the isotropic, nematic, and smectic phases. Molar mass was varied from 3 x 10(5) to 3 x 10(6) g/mol, corresponding to the range where the onset of entanglement is observed in the isotropic phase (approximately 1-10M(e,iso)). Nematic order produces a profound change in the dynamics of the entangled SG-LPCs relative to the isotropic phase; however, this effect is absent in the unentangled SG-LCPs. Oscillatory shear with large amplitude (gamma(0) greater than or equal to 40%) is effective in inducing macroscopic alignment in the nematic phase for all the SG-LCPs studied. Smectic order increases the elastic character of the fluid, but its incremental effect in a system that is entangled is relatively small. Large-amplitude shearing can be used to alter the microstructure in the smectic liquid: shearing the smectic phase produces a decrease in modulus, whereas shearing in the nematic phase followed by cooling into the smectic phase produces an increase in modulus.