DEGRADATION OF POLY[BIS(GLYCINE ETHYL ESTER)PHOSPHAZENE] IN AQUEOUS-MEDIA

The degradation of poly[bis(glycine ethyl ester)phosphazene] in aqueou s media was studied by following the appearance of some of its expecte d by-products in solution. Disc-shaped polymer slabs of 12 mm diameter and 1.2 mm thickness were prepared by compression moulding, followed by incubation in aqueous media under carefully controlled conditions o f pH and temperature. Low molecular weight by-products (phosphate and glycine) were assayed for up to 60 d using ultraviolet and visible spe ctroscopy. Slabs placed in pH 12.0 media at 20-degrees-C took 16 d to disappear completely (no longer visible), while at 37 and 47-degrees-C this occurred in 12 d. Also, slabs placed in pH 7.0 and 4.0 media too k 60 and 24 d, respectively, to disappear at 47-degrees-C. However, at 20 and 37-degrees-C only some of the material disappeared at pH 7.0 a fter 60 d. In all cases, the cumulative fractional loss of by-products from the slabs was <1, indicating the presence in solution of other s pecies which were unaccounted for. This study showed that poly[bis(gly cine ethyl ester)phosphazene] slabs have a lifetime in physiological m edia which makes them an acceptable support for short-term controlled drug release, and complements others, in which polyphosphazenes were u sed for a similar application.