Polyferrocenylsilane Microspheres:  Synthesis, Mechanism of Formation, Size and Charge Tunability, Electrostatic Self-Assembly, and Pyrolysis to Spherical Magnetic Ceramic Particles

Pt(0)-catalyzed ring-opening precipitation copolymerization of [1]silaferrocenophanes fcSiMe₂ (3) and the spirocyclic cross-linker fcSi(CH₂)₃ (4) (fc = Fe(η⁵-C₅H₄)₂) was used to prepare polyferrocenylsilane microspheres (PFSMSs) under mild conditions. By varying the reaction conditions, a wide variety of other morphologies was obtained. The effects of temperature, monomer ratio, solvent composition, catalyst concentration, and time on the observed morphology were investigated and interpreted in terms of a mechanism for microsphere formation. The most well-defined particles were formed using equimolar amounts of 3 and 4, in a 50:50 mixture of xylenes and decane at 60 °C with gentle agitation. Chemical oxidation of the polymeric microspheres led to positively charged particles (OPFSMSs) which underwent electrostatically driven self-assembly with negatively charged silica microspheres to form core−corona composite particles. Redox titration with controlled amounts of the one-electron oxidant [N(C₆H₄Br-p)₃][PF₆] in acetonitrile led to the oxidation of the outer 0.15 μm (ca. 32%) of the PFSMSs. The resulting OPFSMSs were reduced back to their neutral form by reaction with hydrazine in methanol. Pyrolysis of the PFSMSs led to spherical magnetic ceramic replicas with tunable magnetic properties that organize into ordered 2-D arrays at the air−water interface under the influence of a magnetic field.