Much of the fundamental work on the formation of the oligomeric chlorophosphazene was performed in the 1960s and 1970s in which they studied the [Cl3P(NPCl2)mCl]+X- oligomers where m&lt;5 in polar solvents such as nitrobenzene and/or symmetric tetrachloroethane (s-TCE). Current synthetic methods use chlorobenzene as a solvent to form the cyclic trimer [PCl2N]3 and higher ring species, of which the trimer is used in a ring opening polymerization. There are at least three possibilities for the ring closure process assuming that the PCl2N unit of the oligomer are retained in the ring product; a spontaneous closure that requires no additional PCl5 or NH4Cl, a ring closure that requires an NH4Cl intermediate that captures both phosphorus terminal ends, and a ring closure that would involve an intermediate that includes the [PCl6]- anion and two NH4Cl molecules to form the cyclic products. Subsequently, the impact of either the Cl- or the PCl6- counter-ion may have an effect on the formation of the cyclic products. The PCl6- ion is a weakly coordinating ion whereas the Cl- is a stronger coordinating ion. Concurrently, the choice of solvent can affect the PCl5 equilibrium and the removal of the solvent may have an effect on the equilibrium distribution of the PCl5 reagent and the counter ions present. We will report a study on the mechanism of the oligomeric chlorophosphazene formation in solution using the analytical techniques of NMR spectroscopy and ESI mass spectrometry, which will also include quantum mechanical calculation studies of the counter-ion and solvent effects of the oligomers. Our results provide a better understanding of the ring closure mechanism of chlorophosphazenes.

Solution chemistry of linear chlorophosphazene oligomers [Cl3P(NPCl2)mCl]+X-

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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