UV Irradiation-Induced Shell Cross-Linked Micelles with pH-Responsive Cores Using ABC Triblock Copolymers

• Published in: Macromolecules 2006-09, Vol.39 (18), p.5987-5994
• Main Authors: Jiang, Xiaoze, Luo, Shizhong, Armes, Steven P, Shi, Wenfang, Liu, Shiyong
• Format: Article
• Language: English
• Subjects: Applied sciences; Copolymerization; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Preparation, kinetics, thermodynamics, mechanism and catalysts
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma061386m

A triblock copolymer, poly(ethylene glycol)-b-poly(glycerol monomethacrylate)-b-poly(2-(diethylamino)ethyl methacrylate) (PEG−PGMA−PDEA), was synthesized via atom transfer radical polymerization (ATRP) by successive polymerization of glycerol monomethacrylate (GMA) and 2-(diethylamino)ethyl methacrylate (DEA) using a PEG-based ATRP macroinitiator. Reacting the obtained triblock copolymer with varying amounts of cinnamoyl chloride in anhydrous pyridine yielded PEG−(PCGMA-co-PGMA)−PDEA triblock copolymer with photo-cross-linkable moieties, where PCGMA is poly(3-cinnamoyl glycerol monomethacrylate) and the mean degree of cinnamoylation ranges from 5 to 50 mol % relative to the PGMA block. All PEG−(PCGMA-co-PGMA)−PDEA triblock copolymers molecularly dissolve in aqueous media at acidic pH; upon addition of NaOH, micellization occurred above pH 7−8 to form three-layer “onionlike” micelles comprising PDEA cores, PCGMA-co-PGMA inner shells, and PEG outer coronas. The pH-induced micellization kinetics of PEG113−(CGMA0.5-co-GMA0.5)50−DEA65 triblock copolymers was investigated by stopped-flow light scattering upon a pH jump from 3 to 10, and compared to that of PEG113−PGMA50−PDEA65. Facile cross-linking of the PCGMA-co-PGMA inner shell was then conducted via UV irradiation. The PDEA cores of the resulting shell cross-linked (SCL) micelles exhibited reversible pH-responsive behavior. The extent of pH-induced swelling/shrinking and the colloidal stability of SCL micelles were mainly determined by the extent of cross-linking. The dissociation kinetics of the triblock copolymer micelles before and after shell cross-linking was also investigated employing the stopped-flow technique. It was found that SCL micelles prepared at higher degrees (>20 mol %) of cross-linking exhibited excellent colloidal stability to external pH changes.