Bridge polysilsesquioxane xerogels with a bifunctional surface layer of the ≡Si(CH2)3NH2/≡Si(CH2)3SH composition

Xerogels with a bifunctional surface layer of the ≡Si(CH 2 ) 3 NH 2 /≡Si(CH 2 ) 3 SH composition are synthesized by hydrolytic co-polycondensation of bis(triethoxy)silane (C 2 H 5 O) 3 Si(CH 2 ) 2 Si(OC 2 H 5 ) 3 and two trifunctional silanes, namely, 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane. Using IR, 1 H MAS NMR, and 13 C CP/MAS NMR spectroscopic techniques, it is shown that in addition to complexing groups, the surface layer also contains water, silanol groups that are involved in the hydrogen bond formation and also residual ethoxysilyl groups. According to 29 SiCP/MAS NMR spectroscopic data, the degree of polycondensation of synthesized xerogels exceeds 80%. It is found that the use of 1,2-bis(triethoxysilyl)ethane as the structuring agent in place of tetraethoxysilane allows one to synthesize bifunctional xerogels with the highly developed biporous structure ( S sp = 607–680 m 2 /g, V c = 1.38–1.47 cm 3 /g, d = 2.9–3.1 and 18.3 nm). Changing the ratio structuring-silane/functionalizing-silane-mixture from 2: 1 to 4: 1 in the reaction system has virtually no effect on the porous structure parameters of final xerogels.