Direct synthesis of pH-responsive polymer nanoparticles based on living radical polymerization and traditional radical polymerization

Well-defined pH-responsive polymer nanoparticles were prepared in water directly after a simple dialysis procedure without the process of self-assembly from branched copolymers. The branched AB diblock copolymers of poly(ethyleneglycol methacrylate/dimethylamino ethyl methacrylate) (P(PEGMA/DMA)) and poly(ethyleneglycol methacrylate)/diethylamino ethyl methacrylate) (P(PEGMA/DEA)) have been synthesized using a one-pot atom-transfer radical polymerization (ATRP) approach in presence of a bifunctional monomer-ethyleneglycol dimethacrylate (EGDMA). Clear polymer nanoparticle (170 nm-244 nm) suspensions were obtained after a dialysis process. The aqueous solution behavior of the branched and linear copolymers at different pH (pH 3.7-12) was investigated using dynamic light scattering (DLS). pH-responsiveness was observed for both branched copolymer systems. As a comparison, branched copolymers of P(PEGMA/DMA) were also synthesized via traditional radical polymerization (TRP) in the presence of EGDMA, followed by similar dialysis. Most TRP branched copolymers could not afford neat particles and polymers precipitated on increasing the pH above 7.5. The controlled branching structure is suggested as the key point for the direct synthesis of pH-responsive branched copolymer nanoparticles.