Iodine-containing radio-opaque polyphosphazenes

Abstract

The first poly(organophosphazenes) with iodinated side groups for possible use as radio-opaque biomaterials are reported. Depending on the types of side groups present, these polymers may be biostable or bioerodible. Single-substituent polymers with 4-iodophenoxy or 4-iodophenylanaline ethyl ester units as the only side groups were prepared. Although a single-substituent polymer with 3,5-diiodotyrosine ethyl ester groups was difficult to synthesize, probably because of steric hindrance, mixed-substituent polymers that contained the non-iodinated ethyl esters of glycine, alanine, or phenylalanine plus a corresponding iodinated substituent could be synthesized. ³¹P, ¹H, and ¹³C NMR spectroscopy techniques were used to follow the linkage of the side groups to the phosphazene skeleton and to establish the ratios of the different side groups. Hydrolysis of the iodo-amino acid/non-iodinated amino acid side group species in deionized water at 37 °C followed a bulk hydrolysis profile, with the rates dependent on the structure of the side groups. The effectiveness of these polymers as X-ray opaque materials was examined by the use of the poly(organophosphazenes) and conventional organic polymers as filters for copper Kα or rhenium–tungsten–molybdenum radiation. The phosphazene polymers that contained iodine in the side groups were opaque to X-rays, whereas the conventional organic polymers were essentially transparent to the same radiation.