Porosity in Polysilsesquioxane Xerogels
- PDF / 1,028,258 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 22 Downloads / 257 Views
n R-Si(OR')3
+
I R-SiOI. 5J
1.5n H2 0
+
3n ROH
Scheme 1. Hydrolysis and condensation of trialkoxysilanes to give polysilsesquioxane gels. R' = OMe: R = H, methyl, n-hexadecyl, n-octadecyl, vinyl, chloromethyl, (pchloromethyl)phenyl. R' = OEt: R = H, methyl, ethyl, n-hexadecyl, n-octadecyl, vinyl, chloromethyl, cyanoethyl. These polymers have become increasingly popular for generating specialty coatings such as low k dielectric materials for microelectronic applications [3]. While there is extensive information on the formation of polysilsesquioxanes [2], there has not been a survey of the ability of organotrialkoxysilanes to form gels until recently [4,5]. The formation of polysilsesquioxanes gels has been shown to be very sensitive to the nature of the organic group. Many monomers will only form soluble oligomers or polymers upon hydrolysis and condensation, even when the reaction is conducted solvent-free with neat monomer and aqueous catalyst. Furthermore, there is little information on the influence of the organic group, R, on the porosity of the polysilsesquioxanes gels that are formed [6]. In this paper we describe the preparation of
105 Mat. Res. Soc. Symp. Proc. Vol. 576 ©1999 Materials Research Society
polysilsesquioxane gels where R = H, methyl, ethyl, cyanoethyl, vinyl, dodecyl, hexadecyl, octadecyl, chloromethyl, and chloromethylphenyl and the characterization of the porosity of the respective xerogels. Gels were prepared from the hydrolysis and condensation of organotrimethoxysilanes, RSi(OMe) 3, and organotriethoxysilanes, RSi(OEt) 3 . EXPERIMENT General Methods. Anhydrous methanol was purchased from Aldrich. Ethanol was distilled from magnesium before use. 'H nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AM400 (400 MHz) using C6 D6 or CDC13 as solvent. Triethoxysilane, trimethoxysilane, methy ltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, ethyltriethoxysilane, cyanoethyltriethoxysilane, vinyltriethoxysilane, chloromethyltrimethoxyne, chlorotriethoxysilane, chloromethylphenyl-
trimethoxysilane hexadecyltrimethoxysilane, hexadecyltriethoxysilane and noctadecyltrimethoxysilane were purchased from Aldrich. Monomer purities were checked by GC, "3 C and 29Si NMR and the monomers were distilled if necessary until purities greater than 96% (GC) were achieved. Polymerizations. Monomers were generally polymerized with 1.5 equivalents of water in triplicate at IM concentration in the appropriate alcohol (methanol for trimethoxysilanes; ethanol for triethoxysilanes). Aqueous HC1 (IN) and NaOH (IN) were used as catalysts (2.7 mol% catalyst relative to monomer concentration). If gels were obtained, the monomer was then polymerized at lower concentrations to determine where the practical gelation threshold lies. If the monomer did not gel in a week or two, it was then polymerized at as high a concentration as possible (based on the molecular weight and density of the monomer). Gels were described as either colloidal (opaque white) or translucent (blue tinted) or tran
Data Loading...
