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 polyester s with flexible side chains is presented. Investigations in solution h ave been performed using protonated material dissolved in deuterated t etrahydrofuran and deuterated nitrobenzene. To determine the conformat ion 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 dev eloped. It is shown that the form factor measured in solution is compa tible 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 stru ctural studies which indicate that in bulk the side chains of a given main chain are located in a plane; i.e., the polyester molecule assume s 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 exert ed by the neighbouring molecules in the bulk.