Novel amphiphilic diblock copolymer of low molecular weight poly(N-vinylpyrrolidone)-block-poly(D,L-lactide):: Synthesis, characterization, and micellization

Low molecular weight poly(N-vinylpyrrolidone) (PVP) with a hydroxyl group at one end was successfully synthesized by free radical polymerization of N-vinyl-2-pyrrolidone (NVP). Using isopropyl alcohol as solvent and 2-mereaptoethanol as chain transfer agent, a control over molecular weight (MW) profile of PVP was obtained, leading to average-number MW as low as 2500 Da and polydispersity indexes close to 1.5. MALDI-TOF mass spectrometry indicated that the insertion of hydroxyl group on one chain end was quantitative. Hydroxyl-terminated PVP was used as macroinitiator in ring-opening polymerization Of D,L-lactide yielding amphiphilic poly(N-vinylpyrrolidone)-block-poly(D,L-lactide) (PVP-b-PDLLA) diblock copolymer with polydispersity indexes as low as 1.14. PDLLA contents could be tuned according to the feed ratio of DLLA, leading to molar percents up to 47%. The well-defined diblock copolymer self-assembles into micelles in aqueous solution. Polymeric micelles, composed of PVP-b-PDLLA with PVP M of 2500 and PDLLA molar content of 45%, displayed monodispersed size distribution of about 40 nm. The critical association concentration of micelles was determined to be around 6 mg/L.