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  • 1
    ISSN: 0887-624X
    Keywords: thermal degradation ; polysiloxane ; alternating copolymer ; thermal isomerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0887-624X
    Keywords: polysiloxane ; resin ; nonhydrolytic condensation ; 29Si-NMR ; redistribution reactions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Low-viscosity, methoxylated polysiloxane resins incorporating Me2SiO2/2 (D) and SiO4/2 (Q) units were prepared using nonhydrolytic condensation between Si - Cl and Si - OMe groups with the formation of MeCl, catalyzed by a Lewis acid. With the commonly used catalysts, condensation between two Si - OMe groups, with formation of Me2O, also took place to a large extent, hindering the control of the degree of condensation of the resins. Several catalysts were tested by monitoring the formation of MeCl and Me2O using sealed NMR tubes and 1H-NMR spectroscopy. The best compromise between reactivity and selectivity was obtained with ZrCl4. Resins with various compositions were prepared in the absence of solvent by condensation between Me2SiCl2 and Si(OMe)4 at 130°C, catalyzed by 1 mol % ZrCl4. They were characterized using viscosimetry, gas chromatography coupled with mass-spectrometry (GC-MS), and quantitative 29Si-NMR spectroscopy. The resins consisted of a complicated mixture of oligomers, linear or branched (n 〉 1) and cyclic (n 〉 3), with a high degree of D/Q bonding. The distribution of Si - OMe and Si - OSi bonds and the bonding between D and Q units were found to be nearly random. This was ascribed to the occurrence of Si - OSi/Si - OMe and Si - OSi/Si - OSi redistribution reactions that reached equilibrium during the synthesis. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2415-2425, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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