Compositions comprising a polymer-based macroscopically homogeneous polymer alloy comprising a plurality of microcrystalline components dispersed within an amorphous component, which is biocompatible, bioerodable, substantially non-toxic, and excretable, or metabolized when introduced into a mammalian body. In preferred embodiments, malleable molded devices such as implants, films, drug delivery systems and the like, are comprised of the compositions. Methods of making such compositions by controlled cooling of the molten alloy are also described.