Daten zu den Feld-Desorptions-Massenspektren von Oligomeren

Ohne Zusammenfassung     

Monomer Reactivity Ratios for the Copolymerization of p-lsopropylstyrene with Styrene and Methyl Methacrylate

Abstract

The monomer reactivity ratios for the copolymerizations of p-isopropylstyrene with styrene and with methyl methacrylate have been determined by the ionization chamber-vibrating reed electrometer radioactivity assay technique. The values from the differential form of the copolymerization equation are r₁ (styrene) = 1.22, r₂ (p-isopropylstyrene) = 0.89, and r₁ (methyl methacrylate) = 0.44, r₂ (p-isopropylstyrene) = 0.39. The values from the integrated form of the equation are r₁ (styrene) = 1.37 and r₂ = 0.99. These values indicate that, in the copolymerization of p-divinylbenzene (p-DVB) with styrene, the p-isopropylstyrene-like unit, formed from having the first vinyl group of p-DVB reacted, takes part in subsequent propagation reactions with styrene less readily than either styrene or p-DVB.     

ACID-BASE CHEMISTRY OF [PCl2N]3

An understanding of the chemistry of [¹⁵NPCl₂]₃ is very important because this trimer is the major precursor to phosphazene polymers. In order to understand its sensitivity toward reaction conditions, [¹⁵NPCl₂]₃ has been synthesized and characterized by modern spectral techniques. The goal of the study was to detect reactive impurities in the trimer, impurities that may account for the irreproducibility of the ring opening polymerization. Reactions of [¹⁵NPCl₂]₃ with various acids and bases were conducted and the products have been characterized by multinuclear and variable temperature NMR spectroscopy and mass spectrometry. Particular attention was given to understanding the reactivity at the ¹⁵N site toward acid and base reagents.     

Organische S?uren und S?ureanhydride

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Diffusion and point defects in Cu2O

The diffusion of⁶⁴Cu in Cu₂O has been measured by a serial-sectioning technique as a function of temperature (700–1153°C) and oxygen partial pressure (10^?6?8 × 10^2̄ atm). The oxygen-partial-pressure and temperature dependencies of D¹_Cu suggest that both neutral and singly charged copper vacancies contribute to cation self-diffusion. A defect model involving both neutral and singly charged copper vacancies, electron holes, and singly charged oxygen-interstitial ions is developed and fit to the tracer-diffusion data, the electrical-conductivity data (Maluenda et al.), and the stoichiometry data (O'Keeffe and Moore). The resulting defect data are quantitatively consistent with the chemical-diffusion data (Maluenda et al.) and with a correlation factor $\text{f}{}_{\mathrm{v}}\text{=}\text{2}\text{3}$. The defect data are also quantitatively consistent with the high-temperature oxidation studies of copper metal (Iguchi et al.) and with the copper vacancy being 10 times more mobile than the oxygen-interstitial ion at 10002C.     

Morphological Evolution of Single-Crystal Ag Nanospheres during the Galvanic Replacement Reaction with HAuCl(4)

This paper presents a systematic study of the galvanic replacement reaction between 23.5 nm single-crystal Ag nanospheres and HAuCl(4) in an aqueous medium. We have monitored both morphological and spectral changes as the molar ratio of HAuCl(4) to Ag is increased. The replacement reaction on single-crystal Ag nanospheres results in the formation of a series of hollow and porous nanostructures composed of Au-Ag alloys. By varying the molar ratio of HAuCl(4) to Ag, we are able to control the size and density of the pores. In addition, the localized surface plasmon resonance peaks of these nanostructures can be readily tuned from 408 to 791 nm as the product becomes increasingly more hollow and porous.     

Experimental Characterization of Secular Frequency Scanning in Ion Trap Mass Spectrometers

Secular frequency scanning is implemented and characterized using both a benchtop linear ion trap and a miniature rectilinear ion trap mass spectrometer. Separation of tetraalkylammonium ions and those from a mass calibration mixture and from a pesticide mixture is demonstrated with peak widths approaching unit resolution for optimized conditions using the benchtop ion trap. The effects on the spectra of ion trap operating parameters, including waveform amplitude, scan direction, scan rate, and pressure are explored, and peaks at black holes corresponding to nonlinear (higher-order field) resonance points are investigated. Reverse frequency sweeps (increasing mass) on the Mini 12 are shown to result in significantly higher ion ejection efficiency and superior resolution than forward frequency sweeps that decrement mass. This result is accounted for by the asymmetry in ion energy absorption profiles as a function of AC frequency and the shift in ion secular frequency at higher amplitudes in the trap due to higher order fields. We also found that use of higher AC amplitudes in forward frequency sweeps biases ions toward ejection at points of higher order parametric resonance, despite using only dipolar excitation. Higher AC amplitudes also increase peak width and decrease sensitivity in both forward and reverse frequency sweeps. Higher sensitivity and resolution were obtained at higher trap pressures in the secular frequency scan, in contrast to conventional resonance ejection scans, which showed the opposite trend in resolution on the Mini 12. Mass range is shown to be naturally extended in secular frequency scanning when ejecting ions by sweeping the AC waveform through low frequencies, a method which is similar, but arguably superior, to the more usual method of mass range extension using low q resonance ejection.

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