Direct Functionalization of Poly(spirophosphazene)s via the Regioselective Lithiation of the Aromatic Rings Using a...

The direct chemical functionalization of poly(spirophosphazene) [NP(O₂ C₁₂ H₈ )]_n (1) can be performed by the lithiation of the aromatic rings at low temperature using Schlosser's base (Li^t Bu/KO^t Bu or "superbase"), and the subsequent reaction with various electrophiles such as ClSiMe₃ , ClPPh₂ , or MeOB(O₂ C₆ H₁₂ ) (MeOBpin). The functionalized polymers, isolated in very high yields (>90%) and without degradation of the polymeric chains, have an average degree of substitution per repeat unit ranging from 0.3 (random copolymers) to a maximum of 1.0, which corresponds to the homopolymers [NP(O₂ C₁₂ H₇ FG)]_n (FG (functional group) =SiMe₃ , PPh₂ , and Bpin). NMR studies, including bidimensional high temperature experiments on silylated and deuterated polymers, show that the substitution is regioselectively occurring at the C₃ carbon of the aromatic rings due to the coordination of the lithium cations to the nitrogen of the polyphosphazene chain. The introduction of functional groups on the aromatic rings leads to significant changes in the solubility (silylated polymers), T_g , and electronic properties of the material, showing how the change of substituents in the aromatic rings can lead to polyphosphazenes with properties markedly different from those of the precursor polymer.