Polymeric Iron Complex Synthesis
The first polymeric metal complexes prepared by our group in 1995 featured iron tris(bipyridines) with polyoxazoline macroligands. Since that time iron tris(bpy) has served as a model labile system for developing new synthetic methodologies based on numerous controlled polymerization methods (e.g. cationic, ATRP, ROP, anionic) and metalloinitiation, macroligand chelation, and polymer coupling routes. A diversity of iron tris(bpy)-centered star polymers have been generated with good molecular weight and architectural control, based on polyoxazolines, polystyrene, polyacrylates (PMMA, PMA, PtBA), polyesters (PLA, PCL), and polyethers (PEG). Numerous star block copolymers have also been synthesized employing a single polymerization mechanism (e.g. PEOX-PUOX; PCL-PLA) or more than one in combination (PEG-PLA). Recently, sophisticated pentablock bpy macroligands have been achieved, resulting in Fe star polymers with PEG-PCL-PLA arms. Iron-centered heteroarm star polymers are also possible via chelation of bpy centered block copolymers.
Oxazolines: metalloinitiation scheme coming soon
Macroligand chelation scheme coming soon
Polymeric iron tris(bpy) complexes are reactive, stimuli responsive materials. Interestingly, when this classic coordination complex is incorporated into polymers in a well-defined, site-isolated way, unexpected physical properties and reactivity have also been observed. Many polymeric iron tris(bpy) complexes are reversibly thermochromic. Some display solvent and counterion effects, with low extinction coefficients in certain media but typical ones in others. With PEG materials in aqueous environments, unusual air sensitivity has been noted, with chromophore bleaching and enhanced polymer backbone degradation, presumably via a radical mechanism. This has also been exploited for hydrogels incorporating metal coordinate and covalent acrylate crosslinks. Nanostructured films and assemblies have also been generated. Certain patterned block copolymer films can serve as templates for iron mineralization.
Images coming soon
See Publications for many studies featuring polymeric iron tris(bipyridine) complexes.
“Synthesis and Unexpected Reactivity of Iron Tris(bipyridine) Complexes with Poly(ethylene glycol) Macroligands” Pfister, A.; Fraser, C. L. Biomacromolecules 2006, 7, 459-68.
"Iron Tris(bipyridine)-centered PEG-PLA Star Block Copolymers" Fiore, G. L; Klinkenberg, J. L.; Fraser, C. L. Submitted.
“Iron-Centered Star Polymers with Pentablock Bipyridine-Centered PEG-b-PCL-b-PLA Macroligands” Fiore, G. L.; Fraser, C. L. Macromolecules 2008, in press.