AB-INITIO STUDY OF THE STRUCTURE OF POLY[DI(PHENOXY)THIONYLPHOSPHAZENE]

The stable structure of poly[(diphenoxy)thionylphosphazene] single cha ins was modeled with a small molecular compound consisting of one repe at unit of the polymer, The geometrical parameters of the nonplanar '' trans-cis'' conformations of these molecular models were obtained usin g the ab initio molecular orbital theory. The 3-21G() basis set was u sed in the computation. It was found that the phenoxy groups are posit ioned approximately parallel to the backbone and the groups located on adjacent phosphorus atoms point in opposite directions. The bonding o f the short chain segment exhibits a ''single-double'' alternating pat tern 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 c ompound is estimated to be 13 Angstrom.