RIGID-ROD POLYMERS WITH FLEXIBLE SIDE-CHAINS .9. WIDE-ANGLE X-RAY-ANALYSIS OF SIDE-CHAIN ORDERING IN POLY(1,4-PHENYLENE-2,5-DI-N-HEXADECYLOXYTEREPHTHALATE)

Modeling studies were performed for a rigid-rod polyester with hexadecyloxy side chains (n = 16) in order to simulate x-ray scattering curves in the medium angle scattering region (s = 4pi sin THETA/lambda from 0.2 angstrom-1 to 2.2 angstrom-1). The experimental ones were taken from a material obtained by cooling to room temperature from the smectic mesophase at 150-degrees-C. The wide-angle x-ray diffractograms were calculated for given conformations and molecular arrangements using Debye's equation. The theoretical result thus obtained for a great variety of possible packing models and structures was compared to the experimental result. The size of the effective scattering region is found to be 61 x 18 x 52 = 6 x 10(4) angstrom3 and consists of approximately five layers, each of which is composed of two rigid rods and 20 side chains. The planes form by the rigid rods, together with the side chains, have a distance of 3.6 angstrom, the distance between the rods being 26 angstrom. As the main result, it was found that the side chains form regions with a denser ordering (clustering). The interchain distance for side chains decreases in the regions from 5.3 angstrom to 4.8 angstrom.