Experimental and Theoretical Study of the Living Polymerization of N-Silylphosphoranimines. Synthesis of New Block Copolyphosphazenes

Abstract

The sequential living polymerization of N-silylphosphoranimines for the synthesis of polyphosphazene-b-polyphosphazene diblock copolymers (PP-b-PP) has been studied both experimentally and theoretically. For the experiments, BrMe2P═N–SiMe3, [Cl3P═N═PCl3][X] (X = PCl6–, Cl–), Cl3P═N–SiMe3, ClMe2P═N–SiMe3, and [Me3P═N═PMe2Cl]+ were used as representative model reagents. Density functional theory (DFT) calculations in the gas phase adjusted for solvent effects on ClMe2P═N–SiMe3, [Cl3P═N═PCl3]+, Cl3P═N–SiMe3, and ClMe2P═N–SiMe3 confirmed the experimental observations. The results have shown the necessity of starting with mono-end-capped initiators to avoid the formation of triblock chains. It was also demonstrated that the nature of the nucleophilic N-silylphosphoranimines and the electrophilic cationic end groups of the living polyphosphazenes strongly affects the polymerization reaction, imposing limits to its synthetic potential. Thus, good electron donor N-silylphosphoranimines, i.e. XR2P═N–SiMe3, react b...