X-Ray Diffraction Studies of Liquid Crystalline Polymers

Thermotropic liquid crystalline copolyesters display an ordered fluid phase at elevated temperatures which permits the development of unusually high orientation at ambient temperatures. The transition which occurs upon cooling the high temperature nematic liquid crystalline phase very rapidly (e.g. fiber spinning) results in a polymeric glass with nematic structural order. Annealing increases structural order from the nematic glass toward ideal three dimensional crystalline order. Precision X-ray diffractometry has been used to directly observe changes in structural correlations which occur with annealing. Structural transitions range in character in these copolyesters from no change upon annealing to a transition from fully two dimensional to fully three dimensional structural order. Increased three dimensional order also results in substantially increased first order character of the high temperature phase transition. The chemical structure of co-monomers determines, in part, the final degree of dimensionality.