Effect of preparative variables on the properties of poly(dl-lactide-co-glycolide)-methoxypoly(ethyleneglycol) copolymers related to their application in controlled drug delivery.

The effect of certain preparative variables, such as the composition of the feed, the reaction time and the reaction temperature, on the properties of prepared poly(dl-lactide-co-glycolide)-methoxypoly(ethyleneg lycol) (PLGA-mPEG) copolymers and on the yield of the reaction was investigated. The results with regard the molecular weight and yield were discussed in relation to a polymerization mechanism proposed recently (Du et al., 1995. Macromolecules 28, 2124-2132). The higher the PEG content of the feed the lower the molecular weight of the copolymer and the yield of the reaction. The breadth of the molecular weight distribution decreased initially with time, but appeared to stabilize later at low values. Both the ethylene oxide content and the lactide to glycolide molar ratio in the copolymer depended on the reaction temperature and varied with the reaction time. PLGA and mPEG appeared to be partially miscible, and copolymers containing approximately 40% mol or higher ethylene oxide exhibited crystallinity.