Synthesis of Biodegradable Polymers via Metal Complexes Supported by Ferrocene Derived Schiff Base Ligands

In the last few decades, biodegradable plastics have become more common, however, their application is restricted by their limited range of physical properties. To address this issue, new methods and catalysts are required to synthesize variations in the polymer microstructure. Ferrocene-derived Schiff base ligands can provide a redox switch to alter the selectivity of catalysts toward monomers to produce block copolymers. Here, we discuss the synthesis of (salfen)In(OtBu) (salfen = 1,1′-di(2,4-di-tert-butyl-6-iminephenoxy)ferrocene) and its high activity with lactone monomers. Its polymerization rate of -caprolactone, -valerolactone and -butyrolactone is currently among the fastest rates of group 13 catalysts (Chapter 1). The study of (salfan)Zr(OtBu)2 (salfan = 1,1’-di(2-tert-butyl-6-N-methylmethylenephenoxy)ferrocene) demonstrated redox-switchable copolymerization toward lactide and cyclohexene oxide. Using AcFcBArF as a chemical oxidant and CoCp2 as a chemical reductant, ABA and BAB triblock copolymers were synthesized. The protons at the junctions of these blocks were carefully characterized using 2D NMR spectroscopy methods (Chapter 2). A more detailed study of (salfan)Zr(OtBu)2’s copolymerization mechanism with regard to its selectivity of monomers and propensity for side reactions was carried out experimentally and supported by DFT calculations by Junnian Wei (Chapter 3). The side reaction between oxidant and cyclohexene oxide was found to be significant in one-pot reaction conditions and an unusual temperature dependent polymerization of lactide by [(salfan)Zr(OtBu)2][BArF] was found to occur after the polymerization of cyclohexene oxide. Initial investigations into the application of bulk electrolysis to circumvent the need for chemical oxidants and reductants are reported (Chapter 4). And through a collaboration with Spokoyny and coworkers, dodecaborate clusters were found to synthesize extremely high molecular weight polymers of cyclohexene oxide (Chapter 5). Finally, a number of small projects down tangential lines of inquiry surrounding this work are discussed (Appendix F)