Judith Cardoso

Tacticity influence on the electrochemical reactivity of group transfer polymerization-synthesized PTMA.

Spectroscopic, thermal, and electrochemical characterization results are presented for the redox active polymer poly(2,2,6,6-tetramethyl-1-piperinidyloxy-4-yl methacrylate) or PTMA, synthesized by group transfer polymerization (GTP), and its precursors 4-hydroxy-tetramethylpiperidine-N-oxyl (HO-TEMPO) and 4-methacryloyloxy-tetramethylpiperidine-N-oxyl (MO-TEMPO). DSC analysis of synthesized PTMA showed that the glass transition temperature (T(g)) of the polymer structure occurs at 155 °C, corroborated by dynamic mechanical analysis (DMA), which is higher when compared with T(g) data for PTMA synthesized by other methods. Also, the amount of radical species present in PTMA synthesized by GTP reactions (100%) is higher than the values typically upon synthesizing PTMA by radical polymerization. Electrochemical and spectroelectrochemical-electron spin resonance studies in acetonitrile revealed two redox events in the PTMA polymer, one of which is reversible, accounting for ca. 80% of the spins in the polymer and giving rise to the battery behavior. The other redox event is irreversible, accounting for the remaining ca. 20% of spins, which has not previously been reported. These two redox events are linked to a structural property associated with the tacticity of the polymer, where the reversible feature (responsible for cathode behavior) is the dominant species. This corresponds to a number of isotactic domains of the polymer (determined by high temperature (1)H NMR). The second feature accounts for the three-line impurity observed in the ESR, which has been reported previously but poorly explained, associated to the number of heterotactic/syndiotactic triads.

Ethylene Glycol-Citric Acid-Silica Hybrid Organic-Inorganic Materials Obtained by the Sol-Gel Method

The combination of inorganic polymeric networks with organic molecules leads to hybrid materials. Tetraethoxysilane (TEOS) was used as the precursor for the inorganic component, covalently bonded to ethylene glycol (EG) and citric acid (CA) molecules, whose esterification provides the in situ water for hydrolysis of TEOS. Ethanol was added in various amounts to the TEOS-EG-CA mixtures in order to induce different molecular separations among the reacting molecules, thus modifying the molecular weight distributions of the resulting materials.Characterization of these hybrid materials was performed by several techniques, with consistent results among them.The materials obtained are thermoplastic systems which can be used as coatings, or as bulk materials. In particular, their rheological and thermal properties suggest their possible use as components of drilling fluids in the tertiary recovery of petroleum.

Synthesis and processing of the (ethylene‐vinyl acetate‐vinyl alcohol) terpolymer and its blends with a polyamide and styrene copolymers

In this article, the synthesis and properties of the (ethylene-vinyl acetate-vinyl alcohol) terpolymer are studied in detail. A transesterification reaction with alcohols was conducted on poly(ethylene-vinyl acetate) to obtain terpolymers with varying hydroxide contents through three different routes: in solution, in a mixing chamber, and in a twin-screw extruder. The kinetics of the reaction in the mixing chamber are compared with those of the twin-screw extruder. Mechanical and rheological properties of the terpolymer are examined as a function of conversion. Blends of the terpolymer with polyamide (Nylon-6) were prepared for various compositions. They show a steep reduction in the equilibrium torque with respect to that of the polyamide. A region of compatibility at high polyamide contents gives rise to an increase of some mechanical properties above the simple mixing rule (Youngs modulus). On the other hand, blends with poly(styrene-acrylonitrile) and poly(styrene maleic anhydride) show a region of compatibility at equal proportions of the styrene copolymers and with 10% terpolymer content, induced by the reaction of the hydroxide and maleic anhydride groups. This reaction is inhibited at high styrene-acrylonitrile concentrations due to interference presented by the effect of interactions between the maleic anhydride and acrylonitrile groups.

Nanocomposite polymer electrolytes based on poly(poly(ethylene glycol)methacrylate), MMT or ZSM-5 formulated with LiTFSI and PYR11TFSI for Li-ion batteries

Novel poly(poly(ethylenglycol)methacrylate) (pPEGMA) nanocomposite electrolytes (NE) based on montmorillonite (MMT) and zeolite (ZSM-5) with lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (ionic liquid, PYR11TFSI) are synthetized using two different routes. Sonication technique is successfully used to introduce the fillers into the polymer matrix, provide uniform dispersion and shatter aggregates of nanofillers to ensure a polymer amorphous structure. The influence of the inorganic particle content (1, 3 and 5 wt%) and filler structure are discussed in terms of their thermal and morphological properties. SEM and TEM techniques reveal an efficient embedding of the fillers into pPEGMA, whereas analyses conducted with TGA/DSC, FTIR and XRD showed that for the binary systems BN-MMT and BN-ZSM-5 containing LiTFSI, the morphology of pPEGMA results into a crosslinking amorphous matrix where Li+ ion motion is hindered. This behavior stems from a strong interaction between the surface of the anionic nanofiller with methylene (CH2) groups from pPEGMA, and particularly anionic nanofiller with Li+. The addition of ionic liquid (IL) PYR11TFSI to ternary systems TN-MMT and TN-ZSM-5 abates the aforementioned interactions and leads to an increase of the interfacial layer separation, which grants flexibility to the polymer chains. These effects stem significantly enhancements in the ionic conductivities of TN-MMT (4.0 × 10−4 S cm−1) and TN-ZSM-5 (9.4 × 10−6 S cm−1) at 30 °C. The lower conductivity obtained for TN-ZSM-5 in comparison to TN-MMT is explained by considering that the introduction of (PYR11)+ to the host channels is blocked, since (PYR11)+ is larger compared to the diameter channel of ZSM-5 (≈0.56 nm), whereby only Li+ ions outside ZSM-5 can be efficiently transferred. Anisotropic conductivity is exhibited for these NE occurring by hopping motion through the formation of a weak coordination shell formed between ether oxygen and carbonyl oxygen from pPEGMA chain. These materials present adequate morphological, thermal and mechanical properties, and a significant enhancement of Li+ ion conductivity for green materials at room temperature to be considered as potential NE for Li-ion batteries.

Planck intermediate results IX

Using precise full-sky observations from Planck, and applying several methods of component separation, we identify and characterise the emission from the Galactic “haze” at microwave wavelengths. The haze is a distinct component of diffuse Galactic emission, roughly centered on the Galactic centre, and extends to | b | ~ 35−50° in Galactic latitude and | l | ~ 15−20° in longitude. By combining the Planck data with observations from the Wilkinson Microwave Anisotropy Probe, we were able to determine the spectrum of this emission to high accuracy, unhindered by the strong systematic biases present in previous analyses. The derived spectrum is consistent with power-law emission with a spectral index of −2.56 ± 0.05, thus excluding free-free emission as the source and instead favouring hard-spectrum synchrotron radiation from an electron population with a spectrum (number density per energy) dN/dE ∝ E-2.1. At Galactic latitudes | b | < 30°, the microwave haze morphology is consistent with that of the Fermi gamma-ray “haze” or “bubbles”, while at b ~ −50° we have identified an edge in the microwave haze that is spatially coincident with the edge in the gamma-ray bubbles. Taken together, this indicates that we have a multi-wavelength view of a distinct component of our Galaxy. Given both the very hard spectrum and the extended nature of the emission, it is highly unlikely that the haze electrons result from supernova shocks in the Galactic disk. Instead, a new astrophysical mechanism for cosmic-ray acceleration in the inner Galaxy is implied.