Synthesis and structure-related adsorption characteristics of bifunctional polysiloxane xerogels with methyl and 3-mercaptopropyl groups.

Dobryanskaya, G. I.; Zub, Yu. L.; Barczak, M.; Dabrowski, A.

Polysiloxane xerogels containing 3-mercaptopropyl and methyl groups in the surface layer were synthesized by the sol-gel method with ethanol used as a solvent and fluoride ion used as a catalyst. It is established that an increase in the relative content of methyltriethoxysilane in the initial reaction mixture results in formation of xerogels with a developed porous structure. The tendency for an increase in other characteristics of porous structure, the sorption volume and pore size, is also observed. The analogous effect is found upon increasing relative content of tetraethoxysilane with a constant ratio between two trifunctional silanes. By means of atomic force microscopy, it is shown that the xerogels are composed of aggregated particles with mean sizes of 35–45 nm. These results correlate with the data of scanning electron microscopy. On the basis of the data of IR spectroscopy and 13C CP/MAS NMR spectroscopy, it is concluded that the surface layers contain not only 3-mercaptopropyl and methyl groups but also silanol groups, a part of the unhydrolyzed alkoxy groups, and water molecules involved in the formation of hydrogen bonds. The results obtained by 29Si CP/MAS NMR spectroscopy testify that, in synthesized xerogels, the structural units of T1 type [(≡SiO)Si(OR′)2CH3 and/or (≡SiO)Si(OR′)2(CH2)3SH, R′ = H, OCH3 or OC2H5] are absent and the structural units of T3 type [(≡SiO)3SiCH3 and (≡SiO)3Si(CH2)3SH] dominate compared to the units of T2 type [(≡SiO)2Si(OR′)CH3 and (≡SiO)2Si(OR′)(CH2)3SH]. These results are an indirect indication of enhanced hydrolytic stability of surface layers in such xerogels.

QUALITATIVE chemical analysis; COLLOIDS; GELATION; POLYMER colloids; THERMAL properties of porous materials; NUCLEAR magnetic resonance spectroscopy; SURFACE area; XEROGELS

Colloid Journal, 2006, Vol 68, Issue 5, p548

1061-933X

Academic Journal

10.1134/S1061933X06050048