Poly[(amino acid ester)phosphazenes]: Synthesis, Crystallinity, and Hydrolytic Sensitivity in Solution and the Solid State

Fifteen different poly [(amino acid ester)phosphazenes] were synthesized to study their crystalline character and hydrolysis behavior in the solution and solid states. The polyphosphazenes synthesized were poly [bis(methyl glycinat-N-yl)phosphazene], poly [bis(ethyl glycinat-N-yl)phosphazene], poly [bis(tertbutyl glycinat-N-yl)phosphazene], poly[bis(benzyl glycinat-N-yl)phosphazene], poly[bis(methyl alaninat-N-yl)phosphazene], poly[bis(ethyl alaninat-N-yl)phosphazene], poly[bis(tert-butyl alaninat-N-yl)phosphazene], poly[bis(benzyl alaninat-N-yl)phosphazene], poly[bis(methyl valinat-N-yl)phosphazene], poly-[bis(ethyl valinat-N-yl)phosphazene], poly [bis(tert-butyl valinat-N-yl)phosphazene], poly[bis (benzyl valinat-N-yl)phosphazene], poly[bis(methyl phenylalaninat-N-yl)phosphazene], poly[bis(ethyl phenylalaninat-N-yl) phosphazene], and poly [bis(tert-butyl phenylalaninat-N-yl)phosphazene]. The fully-substituted polymers were obtained by treatment of poly(dichlorophosphazene) with a large excess of the appropriate amino acid ester. Several of these polymers were crystalline as measured by differential scanning calorimetry and by polarized optical microscopy. Hydrolysis studies were performed to estimate the rates of decomposition of the polymers and the duration over which the polymers maintained their structural integrity. The polymers are potential biomedical materials.