Vernetzung und Abbau von Polyäthylenterephthalat durch Elektronenbestrahlung

Zusammenfassung PÄT-Folien wurden in Luft, Stickstoff und Vakuum bei 20 °C mit 1 MeV-Elektronen bestrahlt. Untersucht wurden Löslichkeit und Viskosität von Proben, die unmittelbar nach der Bestrahlung gelöst wurden.In allen untersuchten Fällen trat bei hohen Bestrahlungsdosen ein unlöslicher, d. h. vernetzter Anteil auf, dessen Ausbildung jedoch durch in den Proben enthaltene Feuchtigkeit verzögert werden kann. Bei niedrigen Bestrahlungsdosen bewirkt Feuchtigkeit einen Abbau des Polymeren, wie durch Viskositätsmessungen gezeigt wird.Aus den Gel-Messungen wurde derp ₀/q ₀-Wert für Bestrahlung in Luft, Stickstoff und Vakuum zu 1,05 bestimmt.Die Änderung des Gel-Anteils bei Lagerung der Proben zwischen Bestrahlung und Lösung wird diskutiert.

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Summary Polyethyleneterephthalate samples were irradiated in air, nitrogen and vacuum at 20 °C with 1 MeV electrons. The solubility of the samples and the viscosity of the solutions were studied immediately after irradiation. At high doses an insoluble crosslinked part was always observed. Crosslinking was delayed by moisture in the samples. At low irradiation doses moisture causes chain scission as shown by viscosity measurements. The ratiop ₀/q ₀ of degradation to crosslinking in the case of irradiation in air, nitrogen and vacuum was found by gel measurements to be 1.05. The insoluble gel-part changes with increasing storage time of the samples between irradiation and solution.

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Herrn Diplom-PhysikerH. Fischer sei an dieser Stelle für wertvolle Anregungen und Diskussionen besonders gedankt.     

Hydroformylation and hydrocarbethoxylation of 1,2-dicarbethoxy-1,2,3,6-tetrahydropyridazine and 1,2-dicarbethoxy-1,2,3,4-tetrahydropyridazine

The unsaturated compounds 1,2-dicarbethoxy-1,2,3,6-tetrahydropyridazine 1 and 1,2-dicarbethoxy-1,2,3,4-tetrahydropyridazine 2 have been hydroformylated and hydrocarbethoxylated in the presence of some well known cobalt, rhodium, palladium and platinum catalysts. The hydroformylation reaction can be tuned by a suitable choice of the catalyst precursor and reaction conditions, thus allowing the synthesis with high selectivity of one of the two possible isomeric aldehydes. The carbonylation reaction is less synthetically useful, since it shows low activity and unsatisfactory chemo- and regio-selectivity. However, the ester 1,2,4-tricarbethoxyhexahydropyridazine 10 can be prepared in good yield from olefin 1 by using the complex [PdCl₂(PPh₃)₂] as the catalyst precursor.     

Proton magnetic shielding and susceptibility effects in single crystals of ferrocene

The proton NMR in single crystals of ferrocene has been studied by multiple pulse techniques at room temperature. In crystals of natural shape with plane faces the angular dependence of the resonance frequency due to the anisotropy of the shielding and due to the bulk susceptibility was found to be of about equal size, making analysis of the data practically impossible. By using a single crystal sphere the shape dependent part of the susceptibility contribution could be eliminated. In addition, the resolution obtained by the multiple pulse technique is considerably higher for spheres than for non-spherical crystals. As the ferrocene molecules rotate rapidly about their fivefold axes at room temperature, the shielding tensor σ must be axially symmetric. Having this in mind, the data could be analyzed to yield both the shielding tensor with Δσ = σ₆ - σ_⊥ = ?6.5 ± 0.1 ppm, σ_iso = ?4.2 ± 0.5 ppm from a spherical sample of TMS and the anisotropy of the susceptibility Δ _x = 30 × 10^?6 cgs units.     

Vibrational and lifetime line broadenings in ESCA

The line profile of the narrow, symmetric 1s line from neon, recorded with the new ESCA instrument with X-ray monochromatization, is analyzed. The natural linewidth of this line is found to be 0.23 ± 0.02 eV, in good agreement with theoretical calculations of the oscillator strengths for Auger transitions and X-ray emission. Spectra from molecules show frequently asymmetric core electron lines under high resolution. This rules out previous explanations based on a chemical influence on the natural lifetime. Contrary to earlier assumptions, vibrational excitations are shown to be important in core electron spectra. For methane, the vibrational energy spacing is large enough to allow the vibrational lines to be partly resolved. Recent results from accurate PNO CI calculations on methane agree well with the experimental findings. The Franck-Condon transitions in the C1s and N1s lines from CO and N₂ are shown to be well described in the harmonic approximation and approximating the potential curves of the highly excited core hole states with the potential curve for the ground state of NO⁺, X¹ Σ⁺. Knowledge of vibrational excitations in core electron spectra is shown to be valuable in the analysis of high resolution X-ray emission spectra of free molecules.     

Silicon clusters: chemistry and structure

The chemical reactions of size selected silicon cluster ions (containing up to 70 atoms) have been studied with a number of different reagents using injected ion drift tube techniques. Both kinetic and equilibrium measurements have been performed as a function of temperature, and the influence of cluster annealing on chemical reactivity explored. Unlike metal clusters, where bulk behavior appears to be approached with around 30 atoms, large silicon clusters (n up to 70) are much less reactive than bulk silicon surfaces. These results suggest that the clusters in the size range examined here are not small crystals of bulk silicon, but have compact, high coordination number structures with few dangling bonds.     

Phosphinsubstituierte Chelatliganden. XVIII. Penta- und Tetracarbonylmetall-Komplexe des Chroms,Molybdäns und Wolframs mit sekundären und tertiären Phosphinothioformamid-Liganden

Phosphine Substituted Chelate Ligands. XVIII. Penta- and Tetracarbonylmetal Complexes of Chromium, Molybdenum, and Tungsten with Secondary and Tertiary Phosphinothioformamide Ligands Mono- and bidentately coordinated phosphinothioformamide complexes are obtained by photochemical substitution of the metal hexacarbonyls M(CO)₆ (M ? Cr ( a ), Mo ( b ), W ( c )). The M(CO)₅ · THF adducts react with secondary thioamides under exclusion of light to give the P-coordinate pentacarbonyl complexes [(CO)₅MPPh₂C(S)NHR¹] (R¹ ? Ph ( 1a – c ), Me ( 2a )). The photoreaction of M(CO)₅ · THF with secondary and tertiary thioamides at low temperatures leads to the formation of the P, S-chelate complexes . The corresponding N-silylated complexes 6a – c (R¹ ? Me₃Si, R² ? Ph) are obtained by direct photosubstitution of M(CO)₆ in cyclohexane solution. The labile bis(thioformamide) complexes [(CO)₄M(PPh₂C(S)NHMe)₂] ( 7a – c , cis-trans isomers) are synthesized in low yields according to the same procedure. The attempted alkylation of the chelate complexes 3a – c remains unsuccessful, whereas the secondary thioformamides react with n-BuLi/CH₂Br₂ to give the methylene bis(thioformirnidoesters) [Ph₂PC(NR¹)S]₂CH₂ (R¹ ? Ph (8), Me ( 9 )) in quantitative yields.     

Die Koordinationszahl von Lanthaniden: Thermodynamik der LnIIIEDTA-Mischkomplexe mit den Anionen der 8-Hydroxychinolin-5-sulfonsäure,Iminodiessigsäure und Nitrilotriessigsäure

The values of ΔG, ΔH and ΔS for the formation of the mixed 1:1:1 lanthanide EDTA complexes with the anions of 8-hydroxyquinoline-5-sulfonic acid, iminodiacetic acid and nitrilotriacetic acid were determined by pH-titrations and a direct calorimetric method. These thermodynamic data are discussed and compared with those for the formation of the Ln(III)EDTA complexes. Contrary to current opinion it is concluded that all trivalent lanthanide aquoions have the same coordination number in dilute solution. However, in the series of the lanthanide EDTA complexes the coordination number changes between Sm and Tb. In this region, equilibria occur between two types of EDTA complexes with different numbers of coordinated water molecules: The corresponding equilibrium constants could be evaluated. The coordination number changes also in many other Ln complexes along the lanthanide series, and similar equilibria occur.