Synthesis of pH-sensitive self-assembled amphiphilic graft copolymers containing 4,4,4,3,3,2-hexafluorobutyl side chains

Abstract

Novel amphiphilic graft copolymers containing 4,4,4,3,3,2-hexafluorobutyl side chains were designed and synthesized via radical polymerizaion of acrylic acid (AA), poly (ethylene glycol) methyl ether methacrylate (PEGMA) and homemade fluorinated macromonomer (PHFBMA-GMA) and the physicochemical properties of polymeric micelles prepared therefrom were investigated. GPC, FTIR and 1H NMR were employed to characterize the structures of the copolymers. Potentiometric titration measurement confirmed that the pH-sensitive segments were successfully incorporated and the copolymer performed pKa similar to the reported values. A series of random copolymers with the same chemical composition were employed to make comparisons with the graft copolymers. The critical micelle concentrations (CMC) of the copolymers at different pH (5.0 and 9.0) were determined by fluorescence spectroscopy and surface tension measurements. CMC values showed a high degree of consistency between these two methods. The results showed that CMC values for random copolymers were one magnitude order higher than that of graft copolymers. Graft copolymers performed lower CMC larger particle size compared to random copolymers. No significant difference was observed among graft or random copolymers. CMC values and particle size increased while zeta potential values showed significant decrement with increasing pH, indicating significant pH-sensitivity of the copolymers. With regard to the influence of the amount and the molecular weight of PHFBMA-GMA on the properties, increasing the amount and molecular weight of PHFBMA-GMA was prone to lower CMC, larger particle size while zeta potential performed no significant change. Transmission electron microscopy (TEM) showed that the morphological shapes of the copolymers performed spherical micelles. The cytotoxicity test showed that the comb-shaped copolymers performed extremely low cytotoxicity.The pH-sensitive self-assembled amphiphilic graft copolymers containing 4,4,4,3,3,2-hexafluorobutyl side chains could be potential candidates for nanotanks, hydrophobic drug carriers or surfactants and their facile preparation might fit for large scale industrialization.