Hyperbranched organometallic polymers: Synthesis and properties of poly(ferrocenylenesilyne)s

A series of hyperbranched poly(ferrocenylenesilyne)s, [(eta(5)-C5H4)(2)FeSi(R)](n) {R = CH3 [1(1)], CH=CH2 [1(V)], n-C8H17 [1(8)], n-C12H25 [1(12)], n-C16H33 [1(16)], n-C18H37 [1(18)]}, was prepared in good isolation yields (up to 77 wt \%) by one-pot coupling reactions of dilithioferrocene with trichlorosilanes. While the polymers with small R groups [1(1) and 1(V)1 were partially soluble, those with Iona alkyl chains [1(m) with m greater than or equal to 8] were completely soluble and readily film forming. The polymers exhibited diagnostic solution properties of hyperbranched macromolecules; for example, 1(18) had a high absolute molecular weight (M-w = 5 x 10(5) Da) but a low intrinsic viscosity ([eta] = 0.02 dL/g). Spectroscopic analyses revealed that the polymers possessed rigid skeleton structures with extended conjugations, with their absorption spectra tailed into the infrared region (> 700 nm). With an increase in the alkyl chain length, the polymer changed from glassy to rubbery state. The polymers lost little of their weights when heated to similar to400 degreesC but ceramized when pyrolyzed at higher temperatures, with ceramization yield increasing with a decrease in the alkyl chain length. Sintering 1(1) and 1(V) in 700-1200 degreesC produced ceramics in similar to50\% yields. Higher temperature pyrolyses favored the formation of ceramics with bigger inorganic nanoclusters and better magnetic performances. The ceramic prepared from the calcination of 1(1) at 1200 degreesC contained large iron silicide nanocrystals and exhibited high magnetizability (up to similar to51 emu/g) but near-zero remanence and coercivity. This ceramic is thus an outstanding soft ferromagnet with a high magnetic susceptibility and practically nil hysteresis loss