Novel linear-dendritic-like amphiphilic copolymers: synthesis and self-assembly characteristics

Novel linear-dendritic-like poly(D or L-lactide)-b-poly(acrylic acid) (l-PD(L)LA-b-d-PAA) amphiphilic copolymers were synthesized for the first time via the combination of single-electron transfer living radical polymerization (SET-LRP), ring-opening polymerization (ROP) and thio-bromo Click chemistry. As a macroinitiator for initiating ROP of lactide, dendritic-like poly(tert-butyl acrylate) (PtBA) with a single focal hydroxyl group (OH-d-PtBA) was first synthesized via the branch and growth, followed by hydrolysis of the PtBA segment to yield the targeted linear-dendritic-like amphiphilic copolymers PL(D)LA-b-PAA. Light scattering and TEM studies revealed that the l-PDLA-b-d-PAA and l-PLLA-b-d-PAA copolymers self-assembled into vesicles in an aqueous environment, respectively. When mixed in a 1 to 1 ratio, the corresponding aggregates changed from vesicles to spherical micelles, possibly due to the formation of a more stable and dense packing of the hydrophobic PLA segments resulted from the stereocomplex between the enantiomeric PLA blocks. Meanwhile, the size of the formed aggregates changed with variation of the pH value, indicating that these aggregates possess the pH-dependent swelling and shrinking properties, which endow the formed aggregates with great potential for a controllable drug delivery system. This new type of amphiphilic block copolymers should find potential applications in the biomedical area due to their unique features.