One-step synthesis of poly(lactic-co-glycolic acid)-g-poly-1-vinylpyrrolidin-2-one copolymers

The radical polymerization of 1-vinylpyrrolidin-2-one (NVP) in poly(lactic-co-glycolic acid) (PLGA) 50: 50 at 100 degrees C leads to amphiphilic PLGA-g-PVP copolymers. Their composition is determined by FT-IR spectroscopy. Thermogravimetric analyses agree with FT-IR determinations. Saponification of the PLGA-g-PVP polyester portion allows isolating the PVP side chains and measuring their molecular weight, from which the average chain transfer constant (C-T) of the PLGA units is estimated. The MALDI-TOF spectra of PVP reveal the presence at one chain end of residues of either glycolic acid-or lactic acid- or lactic/glycolic acid dimers, trimers and one tetramer, the other terminal being hydrogen. This unequivocally demonstrates that grafting occurred. Accordingly, the orthogonal solvent pair ethyl acetate-methanol, while separating the components of PLGA/PVP intimate mixtures, fails to separate pure PVP or PLGA from the reaction products. All PLGA-g-PVP and PLGA/PLGA-g-PVP blends, but not PLGA/PVP blends, give long-time stable dispersions in water.