pH-responsive polymeric vesicles from branched copolymers.

A new type of branched copolymer, poly(l-lactide)--poly(l-glutamic acid) (PLLA-PLGA), based on polypeptide PLGA is synthesized by the ring-opening polymerization (ROP) of -carboxyanhydride of γ-benzyl-l-glutamate (BLG-NCA) with amino-terminated PLLA-NH and subsequent deprotection. The branched copolymer is characterized by H NMR, FTIR and GPC measurements. The self-assembly of the copolymers in aqueous media has been systematically discussed. A pyrene probe has been used to demonstrate the aggregated formation of PLLA-PLGA in solution by measuring the critical micelle concentration (cmc). The morphology and size of the micelles have further been studied by transmission electron microscopy (TEM), dynamic light scattering (DLS) and field emission scanning electron microscopy (ESEM). We demonstrated that the Rh of the vesicle is depending on solution pH and salt concentration. The vesicles show good stability with remained shapes and sizes during the lyophilizing process. These vesicles have great potential in the application of drug delivery.