Synthesis of Polyphosphazene Derivatives via Thiol-ene Click Reactions in an Aqueous Medium

A green route is reported for functionalizing polyphosphazene via the thiol-ene click reaction in an aqueous medium. Poly[bis(allylamino)phosphazene] is used as the precursor polymer, which is easily dissolved in water containing 5% (v/v) phosphoric acid, but barely dissolved in other acidic aqueous solutions with the same pH value. Three thiol reagents, namely, 3-mercapto-1,2-propanediol, 2-mercaptoethoxy ethanol, and l -cysteine, are then reacted with the precursor in the phosphoric acid aqueous solutions. 1 H and 31 P NMR analyses confirm that the allyl polyphosphazene can be quantitatively modified by the mercaptans without hydrolysis degradation during the synthesis and purification processes. Moreover, these polyphosphazenes exhibit higher regioselectivity than those functionalized in organic solvents. This method provides a facile route for the green synthesis of functional polyphosphazenes without organic solvents.