Equilibrium Rigidity of Polyorganophosphazene Molecules

Abstract

The optical anisotropy and orientation angles of polyorganophosphazene (PPhPh) molecules with different lengths and side-chain structures have been investigated by flow birefringence and viscosimetry methods. Quantum-chemical calculations of the optical anisotropy per monomer unit within the polymer fragments with different conformations were carried out. It was shown that both short-range and long-range interactions (i. e. the structure of the polymer backbone and steric interactions between side chains) influenced the conformation of the PPhPh molecules and should be taken into account for the determination of the thermodynamic rigidity value A. The experimental value of A, (50 ± 5)·10–8 cm, obtained by different methods, adequately corresponds to the structure and observed physical parameters of the PPhPh molecules. Molecules of this class of polymers are not rigid chains in a common way (A > 150·10–8 cm), but alternating double bonds of their backbones bring about some increase in the equilibrium rigidity. It can be assumed that, for this class of polymers, the mesogeneity on a molecular level is defined by the strong interactions of fluorine-containing side chains rather than by the rigidity of their backbones.