Synthesis And Self-assembly Of PH-responsive Six-armed Star Triblock Copolymers And Controlled Release Behavior

Stimuli-responsive amphiphilic block copolymers can undergo spontaneous microphase separation to form ordered self-assemblies above their critical aggregation concentration(CAC) in aqueous solution. And the morphologies and properties of this type of self-assemblies can be regulated by environmental stimuli. On the basis of this, we herein report novel self-assembly behavior of p H-responsive amphiphilic six-armed star triblock copolymer s-(PDEA62-b-PMMA195-b-PPEGMA47)6,which was synthesized through ATRP method.By using aqueous p H buffer solutions as selective solvents, effect of p H variation on self-assembly of s-(PDEA62-b-PMMA195-b-PPEGMA47)6 was investigated. It was found that s-(PDEA62-b-PMMA195-b-PPEGMA47)6 had low CAC values in aqueous solutions(0.78-2.5 mg/L) and p H variation of the selective solvents exerts a marked effect on morphologies of s-(PDEA62-b-PMMA195-b-PPEGMA47)6 self-assemblies. s-(PDEA62-b-PMMA195-bPPEGMA47)6 could self-assemble into multicompartment micelles at p H 10.5, vesicles at p H 7.4 and micelles at p H 2.0. The hydrodynamic diameters of both micelles and vesicles could respond to change in environmental p H. Interestingly, the vesicles self-assembled at p H 7.4 could exist reversible vesicle-micelle transition by simply adjusting surrounding p H.Using hydrophobic drug celecoxib as a model guest molecule, loading capacities of s-(PDEA62-b-PMMA195-b-PPEGMA47)6 self-assemblies under the above-mentioned three p H conditions and influence of the presence of the guest molecules on morphology of the self-assemblies were investigated. It was found that loading capacities of the star copolymer were 33-35 wt%(relative to polymer) at p H 7.4, 26-28 wt% at p H 10.5 and 10-15 wt% at p H 2.0. And at p H 7.4, the incorporation of 33 wt% celecoxib didn't change morphology of vesicles evidently. However, at p H 10.5, the presence of 26 wt% celecoxib could lead to the star triblolck copolymer self-assembling into vesicles. The celecoxib release from the loaded self-assemblies was p H-responsive.