Ab initio study of the structure of poly[di(phenoxy)thionylphosphazene]

The stable structure of poly[(diphenoxy)thionylphosphazene] single chains was modeled with a small molecular compound consisting of one repeat unit of the polymer. The geometrical parameters of the nonplanar “trans-cis” conformations of these molecular models were obtained using the ab initio molecular orbital theory. The 3-21G∗ basis set was used in the computation. It was found that the phenoxy groups are positioned approximately parallel to the backbone and the groups located on adjacent phosphorus atoms point in opposite directions. The bonding of the short chain segment exhibits a “single-double” alternating pattern along the backbone. The charge distribution along the backbone is highly polarized. The total dipole moment is oriented parallel to the backbone and is equal to 6.75 debye. The molecular diameter of this compound is estimated to be 13 Å.