Andrea Berenbaum

Application of Ring-Opened Poly(ferrocene)s as Protective Charge Dissipation Coatings for Dielectrics

Numerous satellites providing communication, defense, and meteorological services are currently in the Earths orbit, typically at altitudes of three to six earth radii. These come under the influence of charged particles (electrons, protons, and helium nuclei) originating from the surface of the sun. Satellites immersed in this ambient plasma attain electrical equilibrium via the formation of surface charges. The formation of these charges is to a large extent dependent on the development of photoelectrons originating from the surface of the spacecrafts dielectrics. However, in regions of low sunlight intensity or in periods of intense solar activities, negative charge accumulation can occur on the surface (from low energy electrons) and within the interior (from high-energy electrons) of the dielectrics comprising the satellites thermal blankets, cable coatings, and microelectronic devices. When the potential difference between the satellites dielectrics and the surrounding environment is such that the dielectric strength of the material is compromised, a high-energy arc discharge occurs. These arc discharges are of sufficient energy to generate magnetic interference, material breakdown, and device failure. In fact it is believed that the January 1994 and March 1996 failures on the synchronous-orbit ANIK satellites were due to such high-energy arc discharges. The financial implications of such electronic breakdowns are severe. For this reason a number of studies aimed at understanding the interactions of dielectrics with both high and low energy electrons have been undertaken. Also, it would be very desirable to develop a robust polymeric charge dissipating coating which, when applied to the surface of dielectrics, would remove or prevent the formation of any accumulated charge. Importantly, the coating should not possess sufficient electrical conductivity to adversely influence any nearby radio frequency devices. It should also be noted that charge dissipation materials have a wide array of other potential uses including coatings for circuit boards. Soluble, high molecular weight poly(ferrocene)s, 2, (E = Si, Ge, Sn, P, S, etc.) are now readily available via thermal, transition metal catalyzed or anionic ring-opening polymerization (ROP) of strained ferrocenophanes (1). Subsequent studies have shown that such materials possess a range of interesting properties, including high thermal stability and good processability. As a result of the interacting metal centers present in the polymer backbone, materials such as 2 (E = Si) display electrical conductivities of ca. 10 S cm when doped with I2. [8] Additionally, by varying the nature of the bridging moiety, one can tune the metal±metal interactions, and thus the electronic properties of the resulting material. As a result of these properties, pristine samples of poly(ferrocenylsilane)s, 3 and 4, were investigated as charge dissipation coatings. In this communication, we describe our initial, very promising, results in this area.

Living Anionic Ring-Opening Polymerization of Unsymmetrically Substituted Silicon-Bridged [1]Ferrocenophanes; A Route to Organometallic Block Copolymers with Amorphous Poly(ferrocenylsilane) Blocks

Living anionic ring-opening polymerization methodology for silicon-bridged [1]ferrocenophanes has been extended to unsymmetrically substituted monomers. This permits access to well-defined amorphous poly(ferrocene) homopolymers and organometallic block copolymers, such as polystyrene-b-poly(ferrocenylmethylphenylsilane), with an amorphous poly(ferrocenylsilane) block. This allows phase separation to occur at lower temperatures, which should facilitate applications in which organometallic nanodomains are desirable.

Transition metal-catalyzed ring-opening polymerization (ROP) of strained, silicon-bridged bis(benzene)chromium complexes

Silicon-bridged bis(benzene)chromium complexes (sila[1]chromarenophanes) undergo facile transition metal-catalyzed ROP at ambient temperature in the presence of Karstedts catalyst to yield polychromarenylsilanes, the first homopolymers with main chains of Cr(arene)(2) and organosilane units.