biodegradable poly designed to display two - stage degradation profiles are described . the presence of the anhydride linkages allows a relatively rapid decrease in molecular weight , the extent of which is governed by the concentration of the anhydride linkages along the chain , followed by possible dissolution and a slower degradation of the remaining oligomers , the rate of which is governed by the composition of the polyester prepolymers . methods for the preparation of the poly and their polyester precursors are also described .