Synthesis and characterization of amphiphilic triblock-graft PEG-(b-PαN₃CL-g-Alkyne)₂ degradable copolymers

The study proposes a straightforward strategy for synthesizing novel, amphiphilic triblock-graft PEG-(b-PαN₃CL-g-Alkyne)₂ degradable copolymers. First, this investigation performs copolymerization of α-chloro-ε-caprolactone (αClCL) using α,ω- dihydroxyl-terminated macroinitiator poly(ethylene glycol) (PEG) and stannous octoate as the catalyst. In a second step, the current work converts pendent chlorides into azides by reacting with sodium azide. Finally, various kinds of terminal alkynes react with pendent azides by copper-catalyzed Huisgen's 1,3-dipolar cycloaddition, thus a "click" reaction. These copolymers are characterized by differential scanning calorimetry (DSC), ¹H NMR, IR and gel permeation chromatography. The resulting triblock-graft copolymers exhibit lower crystallinity and melting temperature with respect to the original PEG. The triblock-graft copolymers form micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 1.58-8.62 mg L ^-1, depending on polymer composition. The ¹H NMR spectrum of micelles in D₂O demonstrate only the PEG signal and thus confirm the PCL-g-Alkyne blocks constitute the micelle core, while the central PEG block constitutes the micelle shell. The hydrophilic segment lengths influence the micelle shape. The mean hydrodynamic diameters of micelles from DLS range from 90-200 nm. The work describes drug entrapment efficiency and drug loading content of micelles depending on the composition of triblock-graft polymers. [Figure not available: see fulltext.]