Since the mid 1990s soluble, well-characterized high molecular weight metal-containing and metallosupramolecular polymers have become readily available for the first time, even in some cases, with narrow molecular weight distributions and controlled architectures such as block copolymers. This has led to a rapidly expanding interest in their properties and uses. The review provides a survey of the range of applications for these new materials, which combine the processing advantages of polymers with the functionality provided by the presence of metal centers.

Metallopolymers: New Multifunctional Materials

The organometallic−inorganic diblock copolymer poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFDMS-b-PDMS) with a 1:6 block ratio unexpectedly forms long rodlike micelles rather than spherical structures in a variety of PDMS-selective n-alkane solvents when the solutions are prepared at or near ambient temperature. The cylindrical structures represent the thermodynamically preferred morphology and consist of an iron-rich PFDMS core and a corona of PDMS. The length of the micelles can be varied from 70 nm to 10 μm by altering the method of sample preparation. In addition, the dimensions of the micellar core can be controlled through variations in the length of the PFDMS block, which is achieved by altering the molecular weight of the diblock copolymer while maintaining a constant block ratio. In contrast, when micelles are formed above the Tm of PFDMS (ca. 120−145 °C), spherical aggregates are formed, which suggests that crystallization of the core polymer is the driving force for the formation of wor...

Self-Assembly of Organometallic Block Copolymers: The Role of Crystallinity of the Core-Forming Polyferrocene Block in the Micellar Morphologies Formed by Poly(ferrocenylsilane-b-dimethylsiloxane) in n-Alkane Solvents

The study of metallopolymers has blossomed into a mature field over the last few decades. Especially, polyferrocenylsilane (PFS) chemistry has taken a tremendous leap and continues to raise intense interest. Since the discovery of thermal ring-opening polymerization (ROP) of sila[1]ferrocenophanes, PFSs have been also accessed by anionic, cationic, transition-metal-catalyzed, and photolytic anionic ROP methodologies. A plethora of synthetic strategies have been devised, enabling access to a wide variety of copolymers, polyelectrolytes, and nanostructured materials. The distinctive physical properties and functions of many PFS-based polymers have been explored, leading to their apt exploitation in technical applications. Therefore, it is conceivable that PFS-related platforms might be indispensable nano-objects in the near future, as they stand on the verge of a new generation of sophisticated materials.

Polyferrocenylsilane-based polymer systems.

The need for uniform criteria, or guidelines, to be used in all phases of spacecraft design is discussed. Guidelines were developed for the control of absolute and differential charging of spacecraft surfaces by the lower energy space charged particle environment. Interior charging due to higher energy particles is not considered. A guide to good design practices for assessing and controlling charging effects is presented. Uniform design practices for all space vehicles are outlined.

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Design guidelines for assessing and controlling spacecraft charging effects

This in-depth review covers progress in the area of polyferrocenylsilanes (PFS), a well-established, readily accessible class of main chain organosilicon metallopolymer consisting of alternating ferrocene and organosilane units. Soluble, high molar mass samples of these materials were first prepared in the early 1990s by ring-opening polymerisation (ROP) of silicon-bridged [1]ferrocenophanes (sila[1]ferrocenophanes). Thermal, transition metal-catalysed, and also two different living anionic ROP methodologies have been developed: the latter permit access to controlled polymer architectures, such as monodisperse PFS homopolymers and block copolymers. Depending on the substituents, PFS homopolymers can be amorphous or crystalline, and soluble in organic solvents or aqueous media. PFS materials have attracted widespread attention as high refractive index materials, electroactuated redox-active gels, fibres, films, and nanoporous membranes, as precursors to nanostructured magnetic ceramics, and as etch resists to plasmas and other radiation. PFS block copolymers form phase-separated iron-rich, redox-active and preceramic nanodomains in the solid state with applications in nanolithography, nanotemplating, and nanocatalysis. In selective solvents functional micelles with core–shell structures are formed. Block copolymers with a crystallisable PFS core-forming block were the first to be found to undergo “living crystallisation-driven self-assembly” in solution, a controlled method of assembling block copolymers into 1D or 2D structures that resembles a living covalent polymerisation, but on a longer length scale of 10 nm–10 μm.

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Polyferrocenylsilanes: synthesis, properties, and applications

FEP Teflon, Mylar and Kapton H are compared from the point of view of charged-area scaling of discharge current pulse properties. The properties measured are peak current, pulse duration, released charge and energy dissipated in a load resistor, all for 20 keV incident electrons at a current density of 80 nA/cm2. In general it is found that the three materials are more similar than dissimilar, and furthermore that this similarity extends to discharge damage as well, the damage being identified as a combination of subsurface filamentary tunnels and surface grooves. The experimental observations are used to motivate a theory of discharge arc propagation in which the propagation velocity is controlled by the rate of removal of excess charge via wave propagation along a filamentary tunnel filled with an overdense plasma.

Surface Discharges on Teflon, Mylar and Kapton

Numerous satellites providing communication, defense, and meteorological services are currently in the Earth's 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 spacecraft's 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 satellite's thermal blankets, cable coatings, and microelectronic devices. When the potential difference between the satellite's 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.

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

The present invention provides a charge monitor for satellites for monitoring build up of electric charge due to charge particle fluxes impinging on the satellite. In one aspect of the invention the charge monitor includes an electrically conducting housing including at least two compartments with each compartment including a dielectric slab contained therein. An electrically conducting electrode is embedded in each dielectric slab a pre-selected distance below a top surface of the dielectric slab, the housing being mountable on a satellite with the top surface of the dielectric slab facing outwardly into space away from the satellite whereby charged particles emitted from sources external to the satellite penetrate the dielectric slab resulting in charge accumulation in each electrically conducting electrode, each electrically conducting electrode being electrically isolated from all other electrically conducting electrodes in the electrically conducting housing. The monitor includes an electrical voltage detector for sensing the floating DC voltage developed on the electrically conducting electrode in each dielectric slab, due to the charge accumulation, and converting the DC voltage into an AC voltage representative of a charge buildup on each electrically conducting electrode.

Satellite charge monitor

A study of arc discharges on various thicknesses of electron-beam-charged Mylar, FEP Teflon and Kapton shows that the peak substrate current and the energy dissipated in a load resistor both exhibit maxima at a particular thickness of the order of 50 ?m, for one set of experiment parameters. The experiments also show that, as thickness increases, this particular thickness is the transition from near-constant to decreasing released charge, and, for Mylar, from decreasing to near-constant arc duration. This transition is interpreted as being caused primarily for thin specimens by punchthrough formation and possibly influenced by the transition from conduction-dominated to emission-dominated charging. Additional low-energy ion exposure is shown to weaken and sometimes eliminate the arc discharges without radically altering the thickness scaling. At low fluxes, the incident ions are focussed into a central spot.

Thickness Scaling for ARC Discharges on Electron-Beam-Charged Dielectrics

Polyferrocenylsilanes [Fe(η-C5H4)2SiMePh]
 n
 (3) and [Fe(η-C5H4)2SiMe2]
 n
 (4) were prepared by transition metal-catalyzed ring-opening polymerization (ROP) and thin films of these materials were studied to investigate their potential utility as protective charge migration coatings for dielectrics. Films (

 $$>$$
 15 μm) of 3 or 4 cast from a concentrated toluene solution coated on Mylar did not experience any arc discharging when exposed to a beam of low energy (20 keV) electrons for a 1 h time period. In order to further investigate the charge migration properties of polyferrocenylsilanes, thick shapes and films of 3 were prepared by mold-extrusion and solution-casting onto a Teflon substrate, respectively. Charge accumulation measurements on 3 using a nonintrusive electrostatic probe showed that even after a 1 h exposure to a 25 keV electron flux, no appreciable charge accumulation existed. The direction of current flow was explored by constructing a device consisting of a film (thickness ca. 100–130 μm) of polymer 3 coating a layer of copper. When positioned beneath a circular mask and exposed to a low energy electron flux (5–25 keV), measurements of the current at the surface of the polymer film either exposed to or not exposed to the electron flux were not significantly different, and the current recorded from the bare copper connection to the ground was significantly (100–1000 times) higher. Although the mechanism of charge migration in polyferrocenylsilanes is not fully understood, these experiments indicated it may arise from a conduction mechanism, however electron scattering may also be involved.

http://waves.utoronto.ca/prof/Balmain/pdffiles/Polyferrocenylsilanes.pdf?origin=publication_detail

Gerald R. Dubois

Papers

Surface Discharges on Teflon, Mylar and Kapton

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

Satellite charge monitor

Thickness Scaling for ARC Discharges on Electron-Beam-Charged Dielectrics

Polyferrocenylsilanes as Protective Charge Migration Coatings for Dielectrics