Kaitian Xu

Hyperbranched Poly(ferrocenylene)s Containing Groups 14 and 15 Elements: Syntheses, Optical and Thermal Properties, and Pyrolytic Transformations into Nanostructured Magnetoceramics

A series of hyperbranched poly(ferrocenylene)s containing elements (E) of groups 14 [E=Si (hb-1), Ge (hb-2)] and 15 [E=P (hb-3), Sb (hb-4)] are prepared in good isolation yields (up to 82wt%) by the salt-eliminative polycoupling of dilithioferrocene with tri-(RECl3) or tetrachlorides of the elements (ECl4). While the polymers with no or small R groups are insoluble or partially soluble, those with long alkyl chains (R=CnH2n+1 with n ≥ 8) are completely soluble and film forming. The polymers exhibit solution properties characteristic of hyperbranched macromolecules: e.g. hb-1(18) shows a low intrinsic viscosity ([η]=0.02dL/g) despite its high absolute molecular weight (Mw=5 × 105). Spectroscopic analyses reveal that the polymers possess rigid skeleton structures with extended conjugations, with their absorption spectra tailing into the infrared region (>700nm). The polymers show good thermal stability with Td up to ~400°C and can be graphitized into iron-containing ceramics when pyrolyzed at high temperatures, with char yields up to ~60wt%. While calcinations of the Si-containing polymers (hb-1) at 1000°C under nitrogen give ceramics containing mostly α-Fe nanoparticles, those of Ge-(hb-2) and Sb-containing polymers (hb-4) are completely transformed into their iron-alloys. The ceramics from the P-containing polymers (hb-3) show diffraction patterns of iron phosphides. Iron silicide nanocrystals of “large” sizes are obtained when the pyrolysis of hb-1 is conducted at a high temperature of 1200°C under argon. This ceramic is highly magnetizable (Ms up to ~51emu/g) and shows near-zero remanence and coercivity; in other words, it is an outstanding soft ferromagnet with a high magnetic susceptibility and practically nil hysteresis loss.

Synthesis and optical properties of hyperbranched polyarylenes

Abstract High molecular weight, hyperbranched polyarylenes were synthesized in high isolation yields by the copolycyclotrimerizations of 2,5-diethynylthiophene (1), 4,4′-biphenyldiyne (2), and 2,7-diethynylfluorenes (3) with 1-heptyne (4) and 1-dodecyne (5) using TaCl5–Ph4Sn as the catalyst in toluene. The structures of the polymers were characterized by IR, NMR, TGA, and UV analyses. All the polymers exhibited outstanding thermal stability and emitted strong blue light, whose intensities are higher than that of poly(1-phenyl-1-octyne), a well-known highly emissive polyacetylene. Little red shift was observed in the photoluminescence of the polymer thin films. The polymers strongly attenuated intense pulses of 532 nm laser pulses.

Nanostructured magnetoceramics from hyperbranched polymer precursors

Abstract Controlled pyrolysis of a hyperbranched polysilyne, poly[1,1′-ferrocenylene(methyl)silyne] (1), at high temperature in inert atmosphere produces nonostructured ceramics (2) in ∼48–62% yields. The ceramic products 2 are characterized by SEM, XPS, EDX, XRD, and SQUID. It is found that the ceramics are electrically conductive and possess a mesoporous architecture. The iron contents of 2 estimated by EDX are 36–43%. The nanocrystals formed in the ceramics produced under nitrogen 2N are mainly α-Fe2O3 whereas those in the ceramics produced under argon 2A are mainly Fe3Si. When magnetized by an external field at room temperature, 2A exhibits a high saturation magnetization (Ms∼49 emu/g) and near-zero remanence and coercivity.