Synthesis, self-assembly, and pH-responsive behavior of (photo-crosslinked) star amphiphilic triblock copolymer.

Conventional polymeric micelles employed as drug carriers suffer from the drawback of disaggregation when diluted into body fluids, giving rise to premature release of drugs. In this work, cinnamate was chosen as a crosslinker to overcome this issue and regulate pH response. A series of photo-crosslinkable star amphiphilic triblock copolymers, star poly(ε-caprolactone)-b-poly(2-cinnamoyloxyethyl methacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate) (SPCL-b-PCEMA-b-PDMAEMA), were prepared by combination of stepwise reversible addition-fragment chain transfer (RAFT) polymerization and carbodiimide-mediated coupling reaction. These star amphiphilic copolymers could self-assemble into core-shell-corona micelles. Facile photo crosslinking of the micelles was carried out via UV irradiation. The crosslinked micelles showed an improved stability determined by critical micelle concentration (CMC). The degree of photo crosslinking was easily regulated by tuning UV irradiation time, and the hydrodynamic diameters (D(h)) decreased with increasing degree of photo crosslinking. The pH responses of micelles were investigated by dynamic light scattering (DLS), indicating pH-induced swelling-shrinking behavior. For photo-crosslinked micelle, its capability of swelling-shrinking weakened with increasing crosslinking degree, suggesting that pH response was controlled by crosslinking density. This novel photo-crosslinked micelle system with adjustable pH response was expected to have potential as drug carriers for controlled release.