A Structural, Dft And Experimental Investigation Of The Ring Stability And Ring-Opening Polymerization Behaviour Of Cyclic Thionylphosphazenes In The Presence Of Lewis Acid Catalysts

A series of cyclic thionylphosphazenes were prepared and density functional theory (DFT) calculations initiated to gain insight into their susceptibility to ambient ring-opening polymerization with Lewis acid catalysts (GaCl3, AlCl3). DFT analyses determined that PBE1PBE-GD3BJ provided the optimal calculated structures for 1, 5, 5' and 8. The gauge-independent atomic orbital (GIAO) method (M05-2X-GD3//PBE1PBE-GD3BJ) provided a good approximation for the 31P NMR resonances. Energy calculations indicate that thionylphosphazene phosphorus substitution promotes heterolytic cleavage of the thionyl S-Cl bond, as does adduct formation with GaCl3 or AlCl3, suggesting that 4 has potential for GaCl3-catalyzed ROP reactions at ambient temperatures. The generation of thionylphosphazene cation from 1 with catalytic quantities of Lewis acids (10:1 GaCl3, AlCl3) initiates the ambient temperature ROP to poly(thionylphosphazene) (2) in a minimum amount of solvent. Polymerization/ depolymerization studies of 1 and 2 in solution was found to be fully reversible in the presence of GaCl3.