Synthesis, thin-film self-assembly, and pyrolysis of ruthenium-containing polyferrocenylsilane block copolymers

Abstract

Polyferrocenylsilane (PFS)-containing block copolymers have previously been shown to self-assemble into metal-rich nanodomains in thin films or the bulk phase. This patterning of the metalloblock can enable the fabrication of arrays of Fe nanoparticles for applications in catalytic carbon nanotube growth. Herein, we report the preparation of block copolymers with a ruthenium-containing polyferrocenylsilane (RuPFMEtS) segment from a polystyrene-block-polyferrocenylmethyl(trimethylsilylethynyl)silane (PS-b-PFMEt(TMS)S) precursor. The latter was prepared via the photocontrolled ring-opening polymerisation of methyl(trimethylsilylethynyl)sila[1]ferrocenophane and a cyclopentadienyl-terminated polystyrene homopolymer. Deprotection of the Si(CH₃)₃ groups from the ethynyl substituents on the PFS block was carried out by using NaOMe. Incorporation of Ru₃(CO)₉H clusters into the block copolymer was achieved by reaction with Ru₃(CO)₁₂ to obtain PS-b-RuPFMEtS. This afforded two block copolymers, highly metallised ruthenium-based segments, PS₂₆₅-b-RuPFMEtS₁₀ and PS₁₉₆-b-RuPFMEtS₃₁, containing ca. 10 and 20% Ru by mass, respectively. Phase-separation of the resulting block copolymers was investigated in the bulk and thin films and was found to yield spherical or cylindrical domains of RuPFMEtS in a PS matrix, respectively. Pyrolysis of PS₂₆₅-b-RuPFMEtS₁₀ and PS₁₉₆-b-RuPFMEtS₃₁ block copolymers at 500 or 800 °C for 2 h led to the formation of either amorphous (ca. 2 nm in diameter at 500 °C) or polycrystalline (ca. 14 nm in diameter at 800 °C) Fe/Ru nanoparticles in a carbonaceous matrix. These NP composites are promising candidates for use as heterogeneous hydrogenation catalysts. The pyrolysed materials were characterised by high resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, selected area electron diffraction, scanning electron microscopy and powder X-ray diffraction.