Elektronenspinresonanz-, Differentialthermoanalyse- und Molekulargewichtsuntersuchungen an mechanisch beanspruchten Kunststoff-Fäden

Zusammenfassung Polyamid-6-, Polyamid-12-, Polyäthylenterephthalat-, Polyäthylen- und Polypropylenfasern werden im Meßkopf eines ESR-Spektrometers gedehnt. Aus dem Auftreten eines ESR-Spektrums während der Dehnung von Polyamid-6 wird auf die Bildung freier Radikale geschlossen, die durch Kettenbrüche in den amorphen Bereichen entstehen. Bei den anderen Substanzen tritt keine oder nur sehr geringe Radikalbildung auf. Dies wird dadurch erklärt, daß nur in Polyamid-6 die Stabilität der kristallinen Bereiche zur Bildung bis zur Bruchdehnung verspannter Kettenmolekeln in den amorphen Bereichen ausreicht. Diese Vorstellung wird durch Bestimmungen der Molekulargewichte und der Kristallinität der gedehnten Proben gestützt.

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Summary Nylon-6, Nylon-12, polyethyleneterephthalate-, polyethylene- and polypropylene fibers are stretched in the cavity of an ESR-spectrometer. The ESR-spectra formed during stretching of Nylon-6 indicate the formation of free radicals by chain scissions in the amorphous regions. With other polymers no or only very weak ESR-signals are observed. It is suggested that the stability of crystalline regions is sufficient only for Nylon-6 to allow the formation of chains in the amorphous regions which are strained up to their breaking elongation. This is confirmed by determinations of molecular weights and crystallinities of the stretched fibers.

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Mit 17 Abbildungen und 2 Tabellen

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Herrn Prof. Dr.K.-H. Hellwege zum 60. Geburtstag gewidmet.     

Syntheses and Crystal Structures of Di‐ and Trimercury Chlorogallates

Mercury(I) chloride reacts with gallium(III) chloride in benzene/1, 2‐dichlorobenzene solution to give the binuclear compound Hg₂(GaCl₄)₂ ( 1 ). Reduction of mercury(I) chloride with mercury in gallium(III) chloride‐benzene mixture leads to the trinuclear compound Hg₃(GaCl₄)₂ ( 2 ). The crystal structures of 1 and 2 were determined by single‐crystal X‐ray diffraction {Hg₂(GaCl₄)₂: triclinic, P1¯, a = 645.21(3), b = 654.44(3), c = 927.17(7) pm, α = 83.526(2)°, β = 74.915(2)°, γ = 61.863(3)°; Hg₃(GaCl₄)₂: monoclinic, P2₁/c, a = 715.79(1), b = 1501.59(4), c = 1421.43(4) pm, β = 98.9798(9)°}.     

An ESR Approach to the Estimation of the Rate Constants of the Addition and Fragmentation Processes Involved in the RAFT Polymerization of Styrene

The reversible‐addition‐fragmentation chain transfer (RAFT) controlled radical polymerization of such vinylic monomers as styrene (= ethenylbenzene) has gained increasing popularity in current years. While there is a general agreement on the mechanism of RAFT polymerization, there is an ongoing debate about the values of the rate constants of its key steps, i.e., the addition of the propagating radicals to the mediator and the fragmentation of the resulting spin adducts. By carrying out an ESR spectroscopic investigation of the AIBN‐initiated polymerization of styrene (AIBN = 2,2′‐azobis[2‐methylpropanenitrile]), mediated by benzyl (diethoxyphosphoryl)dithioformate ( 5 ) as RAFT agent, we were able to detect and characterize four different radical species involved in the process. By reproducing their concentration–time profiles through a kinetic model, the addition and fragmentation rate constants at 90° of the propagating radicals to and from the mediator were estimated to be ca.10⁷ M ^?1 s^?1 and ca. 10³ s^?1, respectively. The validity of the kinetic model was supported by hybrid meta DFT calculations with the BB1K functional that predicted addition‐ and fragmentation‐rate‐constant values in good agreement with those estimated from the ESR experiments.     

Aromatic nucleophilic substitution. Part 3. Preparation of novel 9-oxo-9H-thioxanthene- and 9-oxo-9H-xanthenedicarboximides and -dicarboxylates

By aromatic nucleophilic substitution followed by intramolecular acylation, 9-oxo-9H-thioxanthene- and 9-oxo-9H-xanthene-dicarboximides were prepared from nitro- or chlorophthalimides and the dianions of thiosalicylic and salicylic acids (Scheme). The 9-oxo-9H-thioxanthene-3,4-dicarboximides were converted to 9-oxo-9H-thioxanthene-3,4-dicarboxylic-acid derivatives such as anhydride, esters, and further imides. Some of these derivatives proved to be excellent photosensitizers with special properties such as liquid aggregation form, H₂O solubility, solubility in lipophilic organic solvents and polymers, or bathochromic shifts of the absorption wavelengths.     

Vapor-liquid equilibria for the system water + tert.-pentanol at 4 temperatures

Precise isothermal vapor-liquid equilibrium data at 10, 30, 55 and 70°C for the system water + tert.-pentanol were measured using a computer-operated differential static apparatus. Activity coefficients at infinite dilution were derived from the experimental P − x data in the dilute region using a flexible Legendre polynomial, and the vapor-liquid-liquid locus was derived directly from the P − x data near the liquid-liquid phase boundary. Heteroazeotropic points were measured directly by distillation using a rotating band column. Furthermore the UNIQUAC and the NRTL models were used to correlate the experimental P − x data and to derive the azeotropic data.

Experimental H^E data were taken from literature and used together with the experimental P − x data to simultaneously fit temperature dependent interaction parameters for UNIQUAC and NRTL. The parameters were used to predict the azeotropic composition over a large temperature range. The results were compared with those of a simple analytical thermodynamic equation using only the pure component vapor pressure data, heats of mixing in the heterogeneous region and the azeotropic composition at one temperature.

Heats of mixing were measured at 140°C with the help of a flow calorimeter in order to determine the slope of H^E vs. x₁ in the heterogeneous region. The H^E data were used to check the reliability of the G^E model parameters and the equation to calculate the temperature dependence of the heteroazeotropic composition.     

Cyano-modified pre-coated plates — a medium polar modification for high performance thin-layer chromatography

Summary The introduction of a cyano-modified, pre-coated layer substantially widens the selectivity of stationary phases in thin-layer chromatography. This is a moderately polar sorbent based on silica gel 60, which can be used both in adsorption chromatography and in reversed-phase chromatography. This new pre-coated layer is particularly suitable for separation of steroids, alkaloids and derivatized amino acids. The possibility of separating habitforming drugs and preservatives in the presence of ionpair reagents is also discussed.     

Vicinal13C-13C coupling via nn,nno and cn paths

From the vicinal ¹³C-¹³C coupling constants determined for a series of bi(poly) cyclic azo-, azoxy- and imino-compounds an independent increment for the NN-, NNO- and NC units of ca. 15, 3–4 and ca.8 Hz resp. was deduced.     

Electronic structure of the azide ion using the SCF Xα SW method

The electronic structure of the azide ion is investigated using the SCF Xα scattered wave method. Calculated ionization energies are compared with values determined by electron spectroscopy. Transition state calculations for π_g → π*_u, σ_u → π*_u and σ_g → π*_u single electron transitions yield excitation energies near 5.7, 11.0, and 12.0 eV respectively.