Solvent-free mechanochemical polycondensation to generate tyrosine-based polyphosphoramidates

• Tyrosine-based polyphosphoramidate. • Solution synthesis yields mixtures of linear and cyclic oligomers. • First mechanochemical synthesis of polyphosphoramidates. • Solvent-free route yields high molecular weight polymers (up to ca.10 kDa) • Polymer shows T g = 81 ℃, high char yields, and forms free-standing films. Polyphosphoramidates are polymers featuring phosphorus-nitrogen bonds within their side or main chain, which impart unique characteristics such as acid-lability and flame retardancy. However, polyphosphoramidates generally require clever design of (P-N)-containing monomers which can then be linked together through conventional polymerisation strategies. Herein, we report the synthesis and characterisation of tyrosine-based polyphosphoramidates with up to ca. 30 repeat units via solvent-free mechanochemically-assisted polycondensation. This polymer synthesis takes advantage of the bifunctional amino and phenolic moieties of tyrosine to form a random copolymer of N-P-N , N-P-O , and O-P-O bonding motifs between tyrosine methyl ester and phenyldichlorophosphate. While polycondensation routes to polyphosphoramidates have been reported previously, this work also represents the first example of a mechanochemical synthesis of a polyphosphoramidate. The use of solid phase synthesis enables the formation of high molecular weight linear species unobtainable under traditional solution phase methods. The obtained polymer exhibits a T g of ca. 81 ℃, resists degradation up to 250 ℃, and has a char yield of 45.0% remaining at 700 ℃ in N 2 . These results demonstrate a solvent-free mechanochemical route to partially bio-based polyphosphoramidates.