The stepwise thermal decomposition of [Ni(Py)4]Br2 was studied by means of a derivatograph. By the introduction of a larger halide atom than C1 the degradation mechanism became simpler. The solid intermediates and the starting material was also analysed with X-ray powder diffraction methods and the unit-cell dimensions were calculated.In a previous work [1] we have investigated a large group of solid Mepyridin-halide-complexes. We carefully studied the thermal decomposition and the solid intermediates formed of the Ni-pyridin-cMoride system [2]. In order to observe the influence of a larger halide atom than chloride we prepared and studied the stepwise degradation properties of the bromide analogue. The starting material and the intermediary compositions which were obtained with the freezing-out technique were further analysed with XRD-powder methods. ExperimentalThe intermediates can not be prepared from solution. Their isolation is possible only by means of derivatograph freezing at the appropriate minima John Wiley & Sons, Limited, Chichester Akaddmiai Kiad6, Budapest

Nach FINKBEINER und KLEBE 1) ist es moglich, Trimethylsilylcellulose mit Hexamethyl-disilazan in Hexamethyl-phosphoramid darzustellen. Das Reaktionsprodukt ist in einigen apolaren Losungsmitteln loslich.Da Hexamethyl-disilazan ein relativ inaktives Silylierungsmittel ist, hielten wir es von Interesse zu untersuchen, welche Rolle die Losungsmittel bei dieser Silylierungsreaktion spielen, ob sie z. B. eine aktivierende Wirkung auf das Hexamethyl-disilazan ausuben oder ob die Losungsmittel nur die Struktur der Ausgangs-Cellulose durch eine quellende Wirkung fur die Silylierungsreaktion auflockern.Hexamethyl-phosphoramid (HMPT) gehort zu den aktivsten Losungsmitteln. Die polare PO-Bindung besitzt Doppelbindungs-Charakterz). 8

It was proved experimentally that isotherms obtained from the results of isothermal thermogravimetric analysis are suitable for the characterization of silicone rubbers used in industry. The experimental results provide a possibility for the calculation of overall (apparent) reaction rate constants, characteristic of the thermal decomposition process, and for the calculation of half-life values in conjunction with the service life. Comparisons of the isotherms and of the characteristic calculated values demonstrated the effects of the parameters of silicone rubber preparation and of the conditions of application on the thermal stability.It was presumed on the basis of earlier work [1] that isothermal thermogravimetric measurements permit the characterization not only of silicone elastomers in the uncured state, but also of the finished products. At a given temperature, the overall reaction rate constant calculated from the experimental results yields numerical values relating to the changes caused by heat in the original properties of the silicone rubber, and to its thermal stability. In the recorded results, the thermal decomposition processes are manifested as the sum of the partial decomposition processes of the rubber components [2].On the basis of literature data and our own experiments, we earlier described [1] that decomposition isotherms determined by isothermal thermogravimetry are of S-shape, and, depending on the time of analysis, reflect three kinds of processes:1. evaporation of volatile components, 2. thermal decomposition, 3. thermal oxidation. The latter two processes are not always clearly separated from one another. When our measurements were performed over 24 hours in the way described in [1], it was possible to follow only the first and second processes. Evaporation proceeds in a relatively brief time, in the initial section of the measurements.The chemical changes of the substance are reflected by the second, approximately straight section of the isotherm. The thermal decomposition of silicone polymer canJohn Wiley & Sons, Limited, Chichester Akad~miai Kiad6, Budapest

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