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  • 1
    Electronic Resource
    Electronic Resource
    29Si and 17O NMR investigations on Si−O−Ti bonds in solutions of diphenylsilanediol and titanium-tetra-isopropoxide (1996)
    Springer
    Journal of sol gel science and technology 6 (1996), S. 139-149 
    Details
    ISSN: 1573-4846
    Keywords: titanosiloxanes ; siloxanes ; hydrolysis ; condensation ; structural units ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The structural units in diphenylsilanediol/titanium-isopropoxide solutions with molar ratio Si:Ti between 1:0.1 and 1:5 were examined by means of 29Si and 17O NMR. The main component in solutions with molar ratio Si/Ti=1:0.1 is the chain-like octaphenyltetrasiloxanediol. With increasing Ti-isopropoxide content (1:0.25–1:05) Si−O−Ti units of the spirocyclic titanosiloxane Ti[O5Si4(C6H5)8]2 prevail in the solutions accompanied by the chain-like tetrasiloxanediol. The 29Si NMR spectra of 1:1 solutions indicate a lot of different Si containing building units with chemical shifts mainly between-40 and-46 ppm. The signals with a chemical shift between-40 and-46 ppm are probably caused by Si atoms which are connected via oxygen bridges directly (Si−O−Ti) or indirectly (Si−O−Si−O−Ti) with titanium. Contrary to the 1:1 solutions only one or two different species with Si−O−Ti units are present in high Ti-alkoxide containing solutions (1:5). 29Si and 17O NMR results reveal a quick hydrolysis of the Ti−O−Si bonds to titanium-oxo-hydroxo-polymers and phenylsiloxanediols or their isopropyl esters after the addition of water to the solutions. This separation into species only containing either Ti−O−Ti or Si−O−Si bonds can entail a decreased homogeneity of the reaction products on a molecular level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425971
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  • 2
    Electronic Resource
    Electronic Resource
    On the Existence and Hydrolytic Stability of Titanosiloxane Bonds in the System: Glycidoxypropyltrimethoxysilane-Water-Titaniumtetraethoxide (1998)
    Springer
    Journal of sol gel science and technology 13 (1998), S. 37-43 
    Details
    ISSN: 1573-4846
    Keywords: heterometal bond ; hydrolysis ; condensation ; 17O and 29Si NMR ; titanosiloxane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Heterometal materials based on glycidoxypropyltrialkoxysilane and titaniumalkoxide are used for optical applications and require a high homogeneity on the molecular level. The presence of heterometal titanosiloxanes, their distribution and hydrolytic stability should influence the homogeneity of these materials. 29Si and 17O NMR spectroscopy has been used to investigate sols with molar ratios Si : Ti = 1 and H2O : OR (H) = 0.5 − 2.0 and their gels after heat treatment at 130°C. The presence of Si—O—Ti bonds in sols with a low water content (H 〈 0.2) and in the corresponding gels was identified by the high-field shift of the 29Si NMR signals of T1 and T2 units of up to 2–3 ppm compared to corresponding signals of homo-condensed Si—O—Si bonds. The existence of Si—O—Ti bonds in the sols is supported by 17O NMR spectra which show a characteristic signal around 340 ppm. A cleavage of the Si—O—Ti bonds occurs with increasing water/OR ratio in the sols. The cleavage of the heterometal bonds and the building up of homo-condensed species leads to a separation into areas with predominantly Ti—O—Ti and Si—O—Si bonds resulting in a decreased molecular homogeneity of the materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008638918967
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  • 3
    Electronic Resource
    Electronic Resource
    The Effect of Nanoscaled Metal Oxide Sols on the Structure and Properties of Glycidoxypropyltrimethoxysilane Derived Sols and Gels (2000)
    Springer
    Journal of sol gel science and technology 19 (2000), S. 305-309 
    Details
    ISSN: 1573-4846
    Keywords: epoxide ; ring-opening ; condensation ; NMR ; hardness ; nanoparticles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Glycidoxypropyltrimethoxysilane (GPTS) is frequently used as precursor for the preparation of sol-gel derived nanoscaled hybrid polymers. The influence of nanoscaled metal oxide sols of silica, boehmite, zirconia and ceria on reactions of GPTS in ethanolic hydrolysates and in corresponding gels (epoxide ring-opening, condensation degree) was examined by liquid- and solid-state 13C and 29Si NMR with regard to a better correlation between structure and material properties. Generally, a higher condensation degree of RSi(O0.5)3 units of GPTS is found after addition of metal oxide sols compared to GPTS without additives. The metal oxide sols (10 mole% series) cause an epoxide ring-opening up to 20% in GPTS hydrolysates after 24 h. A nearly complete ring opening was found in the boehmite and silica containing hybrid gels whereas gels containing ceria and other types of silica only show a low degree of ring-opening. The results show an accelerated ring-opening with increasing content of AlO/OH-species in silica sols. 13C NMR studies reveal that the epoxide ring-opening does not completely lead to polyether structures but to considerable amounts (up to 40%) of ethylether groups which can influence the material properties (hardness).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008777414416
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