CONFORMATION AND SHAPE OF RIGID-ROD POLYESTERS SUBSTITUTED WITH FLEXIBLE SIDE-CHAINS AS REVEALED BY SMALL-ANGLE NEUTRON-SCATTERING

A small-angle neutron study of liquid crystalline main chain polyesters with flexible side chains is presented. Investigations in solution have been performed using protonated material dissolved in deuterated tetrahydrofuran and deuterated nitrobenzene. To determine the conformation in bulk, mixtures of deuterated and protonated material have been investigated at ambient and at elevated temperature. For this purpose, a route for the synthesis of fully deuterated polyesters has been developed. It is shown that the form factor measured in solution is compatible with an extended, rod-like conformation. Investigations in bulk show that a plate-like conformation is adopted under these conditions. This observation is in full agreement with earlier findings from structural studies which indicate that in bulk the side chains of a given main chain are located in a plane; i.e., the polyester molecule assumes a plate-like shape. Thus the present investigation demonstrates that there is a pronounced change of conformation when going from solution to bulk. The reason for this change are the packing constraints exerted by the neighbouring molecules in the bulk.