Poly[N-(2-hydroxypropyl)methacrylamide-block-n-butyl acrylate] micelles in water/DMF mixed solvents

Three diblock copolymers of poly[N-(2-hydroxypropyl)methacrylamide] (poly(HPMA)) and poly(n-butyl acrylate) (poly(BA)) with varying lengths of blocks were prepared by atom transfer radical polymerization. All copolymers were found to be soluble in dimethylformamide (DMF) and poorly soluble or insoluble in water. In water and mixed DMF/H₂O solvents, the copolymers were dispersed in micellar form by controlled addition of water to DMF solutions of copolymers under continuous intensive stirring. The micellar solutions in water were prepared by dialysis of solutions in DMF/H₂O (95 vol% of H₂O) against water. Solution properties of diblock copolymers of poly(HPMA) and poly(BA) were studied using static and dynamic laser light scattering to characterize the behavior of the copolymers at the supramolecular level. The effects of preparation mode, organic solvent (DMF) and copolymer chemical composition on the formation of micelles were studied. While a slower mixing procedure was optimal for copolymers with short poly(HPMA) blocks, a faster mixing was more suitable for copolymers having longer poly(HPMA) blocks. Finally, the dimensions of micelles in water were evaluated. The most compact micelles were prepared from copolymers having short hydrophilic poly(HPMA) blocks. On the other hand, the copolymer with the longest poly(HPMA) block formed micelles with the smallest size and the lowest density.