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SummaryBy means of contact angle measurements, it has been shown that compact alkyl-dimethyl-doxy layers can be obtained on the surface of acid leached glass using the method previously developed for fume silica. Subsequently, a series of densest possible alkyl-dimethylsiloxy layers were prepared having non-branched alkyl substituents, CZH2z+1, (with z = 1, 2, 3, 6 , 10, 14, 18 and 22) and wetting angles were measured as a function of the temperature. On surfaces coated with longer alkyl substituents the formation of mixed crystals, consisting of the sparse chemically bonded alkyl layer and a n-alkane acting as a wetting agent, has been observed at low temperatures. At higher temperatures such surfaces appeared to be 'molten', and at the same time swollen by the wetting agent. Equations have been derived to deduce the free surface energies and to account for the wetting properties of rough and swollen surfaces. Application of the results to the data presented in this paper revealed that glass surfaces covered with short alkyl chains (methyl, ethyl and propyl) are rough and those covered with long chains (tetradecyl, octadecyl and docosyl) are swollen. Surfaces formed by hexyl-and decyl-dimethylsiloxy substituents exhibit intermediate properties.

Summary. The preparation of a series of alkyl-and (mono-, di-and poly-) oxaalkyl-dimethylsilanols is described. The stability of these compounds on storage is considerably increased by previous filtration through a silica gel column.For a study of the reaction of silanols with surface hydroxyl groups of (hydrated) amorphous silicon dioxide, we prepared a series of R-dimethyl-silanols with the following R-substituents:P8 m = 3 P G n = 4 P g m = 4 P 7 n = 5 Of these, trimethylsilanol [l], ethyl-dimethylsilanol [Z] and propyl-dimethylsilanol [3] have been described (see also [4] [S]).The substituents R, to be introduced, were either 1-Bromo-(1A and 1P) or the corresponding 1-vinyl-compounds (2A and 2P). From these, alkyl-dimethyl-chlorosilanes 3A3-3A18 could then be prepared in good yield by reaction of the Grignard derivative of the alkyl-bromides lA3-lAls with dimethyl-dichloro-silane according to reaction (1) [4] [5]:This reaction was not efficacicus for introduction of oxaalkyl substituents. In our attempts to prepare 3 P g in tetrahydrofuran (THF) by reaction (l), a complex mixture resulted, probably because the chlorosilane attacked the solvent, as it is known that dimethyl-dichloro-silane can attack the ether-C-0 bond [6]. In replacing dichlorosilane by dimethyl-diethoxy-silane, the ethoxysilane 4Pg could be isolated from the reaction mixture in good yield.

Die Darstellungen der Alkyl und Oxaalkyldimethylsilanole (VI) werden beschrieben.

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