Synthesis and self-assembly behavior of pH-responsive amphiphilic copolymers containing ketal functional groups

Polymeric micelles that are responsive to pH are particularly attractive for application in drug delivery systems. In this study, one type of amphiphilic block copolymers with hydrophobic building blocks bearing pH-sensitive ketal groups was designed. In an acidic environment, the polarity transfer from amphiphile to double hydrophile for this copolymer destroyed the driving force of micelle formation, which triggered the release of encapsulated hydrophobic molecules. The amphiphilic block copolymers monomethoxy-poly(ethylene glycol)-block-poly(2,2-dimethyl-1,3-dioxolane-4-yl)methyl acrylate (MPEG-block-PDMDMA) was fabricated by atom transfer radical polymerization using MPEG-Br as macroinitiator. The critical micelle concentration of various compositions of this copolymer in aqueous solution ranged from 4.0 to 10.0 mg L-1, and the partition equilibrium constant (K-v) of pyrene in micellar solutions of the copolymers varied from 1.61 x 10(5) to 4.86 x 10(5). Their overall effective hydrodynamic diameters from dynamic light scattering measurements were between 80 and 400 nm, and the micellar morphology showed spherical geometry as investigated using transmission electron microscopy. At pH = 1.0, all of these polymeric micelles presented 100% payload release in 24 h of incubation, while at pH = 3.0, nearly 70 and 25% of pyrene was released for MPEG-block-PDMDMA (44/18) and MPEG-block-PDMDMA (44/25) in 260 h, respectively. The pH-responsive MPEG-block-PDMDMA polymeric micelles having good encapsulation efficiency for hydrophobic drugs are potential candidates for biomedical and drug delivery applications. (C) 2010 Society of Chemical Industry