Iron-Centered Star Polymers with Pentablock Bipyridine-Centered PEG-PCL-PLA Macroligands

Abstract

Elaborate biocompatible block copolymer architectures are achievable via controlled ring opening polymerization (ROP). Selective incorporation of donor groups results in macroligands that can coordinate metals to form site-isolated metallopolymers. A hydroxyl-functionalized bipyridine, bpy(CH2OH)2, was employed as an initiator for the ROP of ethylene oxide, producing bpyPEG2. Subsequent reaction with ε-caprolactone followed by lactide (d,l- and l-) results in well-defined bpy-centered triblock PCL-PEG-bpy-PEG-PCL and pentablock PLA-PCL-PEG-bpy-PEG-PCL-PLA and PLLA-PCL-PEG-bpy-PEG-PCL-PLLA macroligands, respectively, with low polydispersity indices (PLA = d,l-polylactide, PCL = poly(ε-caprolactone), PEG = poly(ethylene glycol), PLLA = l-polylactide). These systems were combined with FeCl2 to produce iron-centered star blocks [Fe{bpy(PEG-PCL)2}3]Cl2, [Fe{bpy(PEG-PCL-PLA)2}3]Cl2, and [Fe{bpy(PEG-PCL-PLLA)2}3]Cl2 with six diblock and triblock arms. Materials were characterized by gel permeation chromatography (GPC), 1H NMR, and UV−vis spectroscopy, verifying that synthetic targets were achieved. Thermal gravimetric analysis shows decomposition temperatures corresponding to PEG, PCL, and PLA blocks, and melting temperatures are typical for these materials.