Hyperbranched polyethoxysiloxane

M., From a Hyperbranched Polyethoxysiloxane Toward Molecular Forms of Silica A Polymer-Based Aproach to the Monitoring of Silica Properties. In Silicones and Silicone-Modified Materials, Clarson, S. J. Fitzgerald, J. J. Owen, M. J. Smith, S. D., Eds. American Chemical Society Washington, DC, 2000 Vol. 729, pp 503-515. 

From a Hyperbranched Polyethoxysiloxane Toward Molecular Forms of Silica A Polymer-Based Approach to the Monitoring of Silica Properties... 

Synthesis of a new modification of silica soluble in THF is described. At the first synthetic step, a hyperbranched polyethoxysiloxane (HBPES) is synthesized by heterofunctional condensation using triethoxysilanol previously generated in reaction mixture by neutralization of correspondent sodium salt with acetic acid. At this step, the process was monitored by IR spectroscopy, SEC, and Si NMR spectroscopy. At the second step, hydrolysis and intramolecular condensation involving silanol groups is carried out to yield silica sol macromolecules. A SAXS method was used to determine the size and fractal coefficient of trimethylsilated derivatives and silica sols obtained. An atomic-force microscopy imaging of silica sol supported on a mica substrate showed the silica sol particles to be predominantly spherical in shape. Prospects for theoretical, experimental and practical applications of silica sols are discussed. 

Synthesis of a hyperbranched polyethoxysiloxane. Using a method described in (in print.), a specimen of hyperbranched polyethoxysiloxane was prepared the solution of 25.4 g (0.125 mole) of sodiumoxytriethoxysilane (preliminary prepared by interaction of 5.0 g of sodium hydroxide and 26.1 g of tetraethoxysilane) was added dropwise to the solution of 7.9g (0.132 mole ) of acetic acid in 160 ml of dry toluene with stirring at 0 C. Reaction mixture was stirred for another two hours at room temperature. The precipitated CHaCOONa was filtered and washed with dry toluene on the filter. The solvent was evacuated at room temperature. 21.7 (82%) of triethoxysilanol was prepared and used for the hyperbranched polyethoxysiloxane preparation. Probe of prepared triethoxysilanol was dissolved in dry THF and analized by NMR (THF,39.76 MHz) 8 = -78.49 (s,lSi). 17.2 g(1.01 mole) of... 

Trimethylsilylated derivatives were prepared by hyperbranched polyethoxysiloxane probe treatment with excess of trimethyltrifluoroacetoxysilane. Mixture was reflaxed... 

Thus, the hyperbranched polyethoxysiloxane, characterized as a realistic polymeric species, is a basic unit ideally suited for obtaining new molecular forms of silica. Here the molecular forms of silica are understood to mean silica species which are particles of definite size and which may be regarded as individual macromolecules with a specified molecular structure amenable to characterization by instrumental methods of analysis. 

Fig.3 SEC elugrams of trimethylsilylated hyperbranched polyethoxysiloxane (1) and polystyrene MM - 60 000 standart (2)...

The same can be said about the hydrolysis and intramolecular condensation of the hyperbranched polyethoxysiloxane. On the one hand, the completeness of hydrolysis is supported by the IR spectroscopic data (Fig. 4). It is seen in Fig. 4 that virtually no absorption is observed in the region of 3000 cm characteristic of the stretching C-H modes whereas a strong absorption is observed in the region of 3700 3200 cm attesting to the presence of hydroxyl groups. 

SAXS measurements. A whole range of problems relevant to the systems of interest could be solved by use of the small-angle X-ray scattering method. Dilute solutions of the hyperbranched polyethoxysiloxane, its trimethylsilyl derivative (a product of its blocking) and a silica sol (a product of hydrolytic condensation of the starting hyperbranched polyethoxysiloxane) were studied under conditions as specified above. The relevant results are presented in Fig. 5 and 6. 

Fig. 5. Log-log plot of the experimental SAXS curves of hyperbranched polyethoxysiloxane (1) Trimethyl-silyl-terminated of (HBPES) (2) silica sol (3). The set of SAXS curves are normalized at s=lnm ...

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