The effect of certain preparative variables, such as the composition of the feeds, the reaction time, catalyst concentration, degrees Centigrade (degrees C), and the reaction temperature on the properties of prepared polymer poly(lactic acid-glycolic acid-4-hydroxyproline) (PLGA-Hpr), was investigated via direct melt polymerization with stannous chloride as a catalyst activated by a proton acid. The new polymer had pendant amine functional groups along the polymer backbone chain. The results with regard to the inherent viscosity and yield of PLGA-Hpr are discussed in relation to a recently proposed polymerization mechanism. The content of lactic acid, glycolic acid, and 4-hydroxyproline (Hpr) in the copolymer was found to affect the surface and bulk hydrophilicity of various PLGA-Hpr copolymers. The inherent viscosity of the copolymer and the yield of the reaction depended on the reaction temperature and varied with the reaction time. The higher the 4-hydroxyproline content of the feedzaq, the lower the inherent viscosity of the copolymer and the yield of the reaction. When the glycolic acid content was more than 70% or the content of HPr was more than 10%, the polymer changed from hemicrystalline to amorphous. The in vitro degradation rate of the PLGA-HPr copolymers is dependent on the feed ratios of lactic acid and glycolic acid in the polymer chain. Lactic acid-rich polymers are more hydrophobic; subsequently they degrade more slowly. The structure of this polymer was verified by infrared (IR) spectroscopy, proton nuclear magnetic resonance (H-1-NMR) spectroscopy, X-ray diffractometry (XRD), and differential scanning calorimetry (DSC) (c) 2006 Wiley Periodicals, Inc.