The crystal structure of oriented poly[di‐(3,4‐dimethylphenoxy) phosphazene] (PDMP) was determined by x‐ray diffraction. Unit‐cell parameters were found to be a = 15.85, b = 19.43, and c = 9.85 Å. The unit cell is metrically orthorhombic with monoclinic space group P21. There were 48 refinable diffraction spots in the observed reciprocal lattice region, of which 28 were observed and 20 were unobserved. A refined model yielded the following residuals: R(obs) = 0.162 and 0.138. It was shown that a two‐chain unit cell with a [T3C]2 (trans, trans, trans, cis, trans, trans, trans, cis) backbone conformation was the correct structure. The dimethylphenoxy side groups were arranged in nearly parallel planes, slightly off‐normal to the fiber c axis. The polymer chains are extremely tightly packed and contain close but reasonable steric contacts.

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Wide-angle X-ray diffraction (WAXD), small-angle light, light scattering and birefringence were used to investigate the temperature dependence of the morphology of poly[bis(trifluoroethoxy)phosphazene]. Experiments conducted on solution cast films revealed a spherulitic morphology in the range 25-225 °C. Structural changes, associated with the transformation to the mesomorphic state, were found to occur in the temperature range 70-90 °C. Above the melting point, the material was isotropic by optical techniques and amorphous by WAXD. The results are discussed in terms of changes in molecular ordering.

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The crystal structures of cyclobisurethane, C12H22N204, and cyclotetraurethane, C24H44N408, have been determined by single-crystal X-ray diffraction analysis. Intensities were collected with an automated XRD-5 diffractometer using Cu K~ radiation. Cyclobisurethane crystallizes in the monoclinic space group C2/c, with a= 17-330 (2), b=8-866 (1), c= 17.944 (3)~, ,8=91.77 (1) °, and Z=8. Cyclotetraurethane crystallizes in monoclinic space group P21/c, with a= 16-463 (4), b = 9.929 (2), c = 9"464 (2) A, fl= 110-19 (3) °, and Z=2. The structures were solved by direct methods and refined by full-matrix least squares to final R values of 0.056 and 0.055 respectively. The molecules of both structures are linked two-dimensionally into sheets by C=O...H-N hydrogen bonds. However, in cyclobisurethane all urethane groups participate in hydrogen bonding, whereas in cyclotetraurethane one carbonyl oxygen accepts two hydrogens, one from each of the crystallographically nonequivalent nitrogens. The carbonyl oxygen not participating in hydrogen bonding appears to interact weakly with a methylene hydrogen of a molecule in an adjoining layer. Cyclobisurethane furnishes conformational models for regular adjacent reentry chain folding in the corresponding polyurethane system. The hydrogen-bonding patterns from both structures provide possible models for hydrogen bonding within hard segment domains of segmented urethane elastomers. The structures of these two polyurethane oligomers are compared with those of the analogous cyclic polyhexamethylene adipamide oligomers.