Rui Resendes

Supramolecular Organometallic Polymer Chemistry: Multiple Morphologies and Superstructures from the Solution Self‐Assembly of Polyferrocene‐block‐Polysiloxane‐block‐Polyferrocene Triblock Copolymers

The solution self-assembly of an organometallic-inorganic triblock copolymer, poly(ferrocenyldimethylsilane)-block-poly(dimethylsiloxane)-block-poly-(ferrocenyldimethylsilane) (PFDMS-b-PDMS-b-PFDMS, 3b; block ratio 1:13:1; Mn = 2.88 x 10(4) gmol(-1), polydispersity (PDI) 1.43 (gel permeation chromatography, GPC)) was studied in n-hexane, a PDMS block selective solvent. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and TEM with negative staining analysis of these micellar solutions after solvent evaporation revealed the presence of multiple micellar morphologies including spheres, cylinders, and novel flower-like supramolecular aggregates. TEM analysis of samples fractionated by ultracentrifugation and preparative size-exclusion chromatography suggest that the formation of multiple morphologies is a consequence of compositional variations. When micellar solutions were prepared at 50 degrees C (above the glass transition of the PFDMS core-forming block) flower-like micellar aggregates similar to those present in micellar solutions prepared at room temperature also formed. However, after solvent evaporation, TEM analysis of micellar solutions prepared in decane at about 150 degrees C, above the melt temperature of the PFDMS core (ca. 120-145 degrees C), revealed the presence of spherical micelles (when decane solutions at 150 degrees C were rapidly cooled to room temperature) and rod-like cylindrical micelles (when decane solutions at 150 degrees C were slowly cooled to room temperature). In contrast, poly(ferrocenylmethylethylsilane)block-poly(dimethylsiloxane)-block-poly(ferrocenylmethylethylsilane) (PFMES-b-PDMS-b-PFMES, 4; block ratio 1:16:1; Mn=2.90x10(4)g mol(-1), PDI= 1.42 (GPC)) and poly(ferrocenylmethylphenylsilane)-block-poly(dimethylsiloxane)-block-poly(ferrocenylmethylphenylsilane) (PFMPS-b-PDMS-b-PFMPS, 5; block ratio 1:15:1; Mn=3.00 x 10(4) gmol(-1), PDI = 1.38 (GPC)), which possess completely amorphous organometallic core-forming blocks, formed only spherical micelles in hexane at room temperature. These observations indicate that crystallinity of the insoluble polyferrocenylsilane block is a critical factor in the formation of the nonspherical micelle morphologies.

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.

Supramolecular Organometallic Polymer Chemistry: Self-Assembly of a Novel Poly(ferrocene)-b-polysiloxane-b-poly(ferrocene) Triblock Copolymer in Solution.

Micelles with unprecedented flowerlike arrangements of the poly(ferrocene) cores (shown in the TEM image) are among the supramolecular architectures generated in the self-assembly of a novel organometallic triblock copolymer from silicon-bridged [1]ferrocenophane monomers and [Me(2)SiO](3) in hexane, a solvent selective for the central polysiloxane block.

Recording the sound of musical instruments with FBGs: the photonic pickup

Fiber Bragg gratings (FBGs) have previously found many applications as strain and vibration sensors. Here we demonstrate that they may also be employed as pickups for musical instruments and, specifically, for acoustic guitars and solid-body electric guitars. By fixing the FBG to a vibrating part of the instruments body, e.g., near the bridge of an acoustic guitar or on the headstock of a solid-body guitar, a number of sound recordings were made and compared to those obtained with either piezoelectric pickups or with magnetic induction pickups. The change in attenuation at the FBGs midreflection point is found to be correlated to the amplitude of vibration of the vibrating structure of the instrument. Acoustic frequency spectrum analysis supports the observation that the FBG acoustic transducer has a frequency response range that is comparable to those of commercial piezoelectric pickups. The recordings made with FBG pickups were of comparable quality to those obtained with other recording methods.

Electronic properties of semiconducting poly(ferrocenylsilane) thin films with vapor-phase iodine diffusion doping

We report diffusion doping of the semiconducting polymer poly (ferrocenylsilanes), or PFS. We have obtained a steady-state conductivity change of greater than eight orders of magnitude effected through iodine vapor doping of PFS. The sign of thermoelectric power measurements indicates p-type conductivity. The conductivity exhibits an activation energy of ΔE=(0.45–0.65) eV for moderately-doped samples and ΔE=(0.8–0.99) eV for heavily-doped samples. We report sample photoconductivity, which we find to be principally of bolometric origin. We also study the evolution of electrical properties over time: during several days after fabrication, the samples exhibit an irreversible decrease in conductivity which may be attributable to partial iodine desorption. After this aging process, especially noticeable in heavily doped material, the sample properties stabilize, suggesting promise in a range of prospective device applications.

Supramolekulare metallorganische Polymerchemie: Selbstorganisation des neuartigen Dreiblockcopolymers Poly(ferrocen)‐b‐polysiloxan‐b‐poly(ferrocen) in Lösung

Micellen mit blutenformigen Anordnungen der Poly(ferrocen)-Kerne (siehe TEM-Aufnahme) sind nur eines der supramolekularen Gebilde, die bei der Selbstorganisation der Titelverbindung in Hexan, einem fur den zentralen Polysiloxanblock selektiven Losungsmittel, entstehen. Das metallorganische Dreiblockcopolymer wurde aus siliciumverbruckten [1]Ferrocenophanmonomeren und [Me2SiO]3 erhalten.

Highly Strained Metallocenophanes: Synthesis and Ring-Opening of Sulfur-, Selenium- and Boron- Bridged [1]Ferrocenophanes

Abstract The limits of cyclopentadienyl ring-tilting in [l]ferrocenophanes are explored with the incorporation of group 16 elements and a first row element. In this paper the synthesis and ring-opening polymerisation (ROP) behaviour of highly strained chalcogen-and boron- bridged [l]ferrocenophanes will be described.

Water-borne coatings that share the mechanism of action of oil-based coatings

Because oil- or solvent-based coatings (e.g. paints, varnishes, sealants) emit volatile organic compounds (VOCs), replacement with aqueous coating formulations is desirable. However, water-based (latex) coatings which are dispersions of polymer particles, are out-performed by solvent-based coatings in hardness, durability, gloss and cold-weather application. The challenge with latexes is that discrete polymer particles must coalesce to form a complete film, a complex process that often leads to imperfections in the coating. Proof-of-concept results show that CO2-responsive copolymers can form the basis of a water-borne coating in which the polymer is fully dissolved before application and yet water-resistant after application to a surface. These polymers are insoluble in neutral water, but dissolve fully in carbonated water. When a carbonated solution of polymer is cast onto a substrate, the subsequent loss of CO2 and water by evaporation results in a clear, continuous water-resistant coating. With further development, these new coatings may retain the VOC-free advantage of water-based coatings while eliminating the need for coalescence of particles.