Synthesis and characterization of amphiphilic block–graft MPEG‐b‐(PαN3CL‐g‐alkyne) degradable copolymers by ring‐opening polymerization and click chemistry

A straightforward strategy is proposed for the synthesis of novel, amphiphilic block–graft MPEG‐b‐(PαN₃CL‐g‐alkyne) degradable copolymers. First, the ring‐opening polymerization of α‐chloro‐ε‐caprolactone (αClCL) was initiated by hydroxy‐terminated macroinitiator monomethoxy poly(ethylene glycol) (MPEG) with SnOct₂ as the catalyst. In a second step, pendent chlorides were converted into azides by the reaction with sodium azide. Finally, various kinds of terminal alkynes were reacted with pendent azides by copper‐catalyzed Huisgen's 1,3‐dipolar cycloaddition, and thus a “click” reaction. These copolymers were characterized by differential scanning calorimetry (DSC), ¹H NMR, IR, and gel permeation chromatography. By fixing the length of the MPEG block and increasing the length of PαClCL (or PαN₃CL) block, an increase tendency in T_gs was observed. However, the copolymers of MPEG‐b‐PαClCL and MPEG‐b‐PαN₃CL were semicrystalline when the M_n of MPEG was above 2000 g mol^?1. The block–graft copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 1.4–12.0 mg L^?1 depending on the composition of polymers. The lengths of hydrophilic segment influence the shape of the micelle. The mean hydrodynamic diameters of the micelles from dynamic light scattering were in the range of 90–160 nm. In vitro hydrolytic degradation of block–graft copolymers is faster than the corresponding block copolymers. The drug entrapment efficiency and the drug loading content of micelles depending on the composition of block–graft polymers were described. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4320–4331, 2008