. . . "In other embodiments, R can comprise substituted or unsubstituted poly(alkylene glycols), which include, but are not limited to, PEG, PEG derivatives such as mPEG, PPG, poly(tetramethylene glycol), poly(ethylene oxide-co-propylene oxide), poly(ethylene glycol-co-hydroxybutyrate), or copolymers and combinations thereof." .