Synthesis and Self-Assembly of Metal Carbonyl Organometallic Macromolecules Prepared via Migration Insertion Polymerization
Migration insertion polymerization (MIP) has been developed for the synthesis of air-stable metal carbonyl polymers. CpFe(CO)₂(CH₂)₃PPh₂ (FpP) was synthesized as a monomer. The solution polymerization of FpP at a monomer concentration of 20 wt% generated PFpP oligomers with a DPn of 11, cyclic molecules, and a fraction of THF-insoluble material. On the other hand, bulk polymerization of FpP resulted in soluble macromolecules and no THF-insoluble material was produced. PFpP with a relatively high molecular weight (Mn = 257,00 g/mol was obtained when FpP was polymerized in bulk at 105 °C in the presence of 5 wt% DMSO. The PFpPs are thermally stable up to 180 °C and have a Tg of 99 °C as indicated by TGA and DSC analysis, respectively. End group analysis suggests that PFpPs possess Fp and phosphine end groups. Taking advantage of the reactivity of the Fp end groups, three PFpP amphiphiles, Ph₂PCn-PFpP (n = 6, 10, 18), were synthesized via migration insertion reactions (MIR) of the Fp end groups with alkyldiphenylphosphines. Moreover, [η⁵-Ph₂P(CH₂)₃C₅H₄]Fe(CO)₂(CH₂)₅CH₃ (FpPCp) with an alkylphosphine group tethered on the Cp ring was synthesized. Bulk MIP of FpPCp resulted in PFpPCp oligomers with a Mn of 4200 g/mol and a PDI of 1.73. Preliminary studies indicated that PFpP was able to self-assemble into uniform and stable vesicles in water. Hydration of the carbonyl groups was deemed to be responsible for the stability of the colloids. Using a nano-precipitation technique, the efficient encapsulation of hydrophilic molecules, e.g., PEG, within PFpP vesicles was achieved.