Atom transfer radical polymerization of potassium 3-sulfopropyl methacrylate: Direct synthesis of amphiphilic block copolymers with methyl methacrylate

The synthesis of potassium 3-sulfopropyl methacrylate (SPMA) homopolymers and amphiphilic block copolymers with methyl methacrylate (MMA) by ATRP in water/DMF mixed solvent at 20 degreesC using a Cu/bipyridine catalyst and halogen exchange is described. SPMA homopolymerization in pure water was poorly controlled even when 200% of Cu(II)Cl-2 with respect to Cu(I)Cl was added, leading to a relatively high polydispersity (1.38). In water:DMF 50:50 (v/v), addition of at least 60% of Cu(II)Cl-2 with respect to Cu(I)Cl allowed to obtain a good control of the polymerization. Linear kinetic plots up to very high conversion were observed and the final polydispersities were relatively low (1.15-1.25). Good self-blocking efficiencies were demonstrated by chain extension experiments even when the first block conversion before the addition of the second feed was very high (>90%). Amphiphilic block copolymers with MMA (number-average degree of polymerization X-n,X-SPMA = 50, X-n,X-MMA = 25) were directly prepared in water:DMF 40:60 (v/v) without using protecting group chemistry or post-polymerization derivatization. The first-order kinetic plot for MMA polymerization was linear up to 96% conversion. Two block copolymers with the same composition, p(SPMA(50)-b-MMA(25))(1pot) and p(SPMA(50)-b-MMA(25))(2pot), were prepared with one-pot and two-pot procedures. p(SPMA(50)-b-MMA(25))(2pot) prepared using a purified pSPMA macroinitiator for MMA polymerization gave well-defined core-shell spherical micelles with an average hydrodynamic radius of about 14 nm determined by dynamic light scattering (DLS) measurements. p(SPMA(50)-b-MMA(25))(1pot) prepared using the sequential monomer addition gave large micellar clusters (more than 100 nm) in addition to simple but smaller micelles. A tentative explanation to the presence of the larger aggregates was given.