Jc. Schrotter et al., SILICON AND PHOSPHORUS ALKOXIDE MIXTURE - SOL-GEL STUDY BY SPECTROSCOPIC TECHNICS, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 4(3), 1995, pp. 195-204
Sol-gel synthesis of mixtures of tetraethoxysilane and a phosphorus al
koxide [P(OEt)(3) or (OEt)(2)P-O-P(OEt)(2) or PO(OEt)(3)] have been st
udied by H-1, (CSi)-C-13-Si-29 and P-31 liquid and solid state NMR, in
frared and raman spectroscopies. This study shows different behaviors
towards hydrolysis for these three different phosphates and phosphites
. P(OEt)(3) almost instantly reacts with water to form an intermediate
species HPO(OEt)(2), which slowly evolves first to HPO(OH)(OEt), then
to HPO(OH)(2) a few days later. For (OEt)(2)P-O-P(OEt)(2), the P-O-P
bond is broken when water is added, then the same intermediates are fo
rmed faster. PO(OEt)(3) is hydrolyzed much slower than the other alkyl
phosphates. After ten months, triethoxyphosphate is quantitatively pr
esent in the sol with little PO(OH)(OEt)(2) species. All these hydroly
zed species are well characterized. Only the system which contains the
tetraethoxysilane and the triethoxyphosphite P(OEt)(3) forms a few P-
O-P and P-O-Si bonds in the gel. Hydrolysis of tetraethoxysilane is mu
ch faster than that of phosphorus alkoxides and the conventional Q(2),
Q(3) and Q(4) condensed silicon species form the gel three dimensiona
l network.