Effect of architecture on the micellar properties of poly (ɛ-caprolactone) containing sulfobetaines

Linear and star-shape poly(ɛ-caprolactone)-b-poly(N-(3-sulfopropyl)-N-methacryloxyethyl-N,N-diethylammoniumbetaine) (L/sPCL-b-PDEAS) with 4 and 6 arms were synthesized with the combination of Ring Opening Polymerization (ROP) and Atom Transfer Radical Polymerization (ATRP). These copolymers self-assembled into micelles via solvent evaporation method. The critical micelle concentration (CMC), determined by fluorescence spectroscopy using pyrene as a probe, was lower than 10(-3)mg/mL and decreased with increasing arm numbers. Atom force microscopy (AFM) images showed that the micelles were spherical in shape with narrow size distribution. The hydrophobic drug model carotene was efficiently loaded in the polymeric micelles. The sizes and drug loading content (DLC) of the carotene-loaded micelles increased with increasing drug content in feed. In vitro drug release experiment demonstrated that the release rate of carotene from the micelles was closely related to the arm numbers and drug loading content. Linear copolymer micelles showed the fastest release rate, 4-arm star shape copolymer micelles exhibited the lowest release rate. The micelles with higher drug loading content showed lower release rate. The release kinetics of carotene from micelles fitted the Ritger-Peppas equation.