MOLECULAR-DYNAMICS AND ORDERING OF SIDE-CHAIN LIQUID-CRYSTAL POLYMERSAS STUDIED BY PARAMAGNETIC-RESONANCE

Molecular dynamics of side chain liquid crystalline polymers (LCP) and their components were studied using the technique of paramagnetic res onance. A cigar shape spin probe (COL) and a nearly spherical spin pro be (TPL) were used to study the motions and order of the LCPs. Compute r simulations of the observed spectra were performed. Both rotational correlation times and order parameters were extracted from these simul ations. We found that LCPs containing 30 per cent and 50 per cent of m esogenic side chains had about the same viscosity as indicated by near ly equal tumbling times at the same temperature. In addition, the LCPs motion is considerably slower than that of the monomeric liquid cryst al indicating that the spacer couples the motions of the side chains t o those of the main chain. Rotations about axes perpendicular to the s ide chain are slowed more than rotations about an axis parallel to the side chain. DSC measurements were employed to study the phase transit ions. The 30 and 50 per cent LCPs displayed first order NS, transition s, but the 50 per cent LCPs transition was much weaker, in agreement w ith McMillan's theory which predicts a first order transition for T-NS /T-NI>0.87 (observed ratios are 0.98, 0.90 and 0.86 for 30, 50 and 100 per cent LCPs, respectively). The 30 per cent LCP has a very short ne matic range so that the nematic order, which is not saturated at the N S transition, can couple with the smectic order. This was indicated by a sharp change in slope of the order parameter versus temperature plo t as the smectic is entered. The LCPs studied formed a highly ordered glass when cooled in a 1 T field. If one could find a LCP with similar ordering properties whose glass temperature is well above room temper ature, then one would have a useful binder for the manufacture of haze -free polymer dispersed liquid crystal displays.