The effect of nanoscaled metal oxide sols on the structure and properties of glycidoxypropyltrimethoxysilane derived sols and gels

Glycidoxypropyltrimethoxysilane (GPTS) is frequently used as precursor for the preparation of sol-gel derived nanoscaled hybrid polymers. The influenc e of nanoscaled metal oxide sols of silica, boehmite, zirconia and ceria on reactions of GPTS in ethanolic hydrolysates and in corresponding gels (epo xide ring-opening, condensation degree) was examined by liquid- and solid-s tate C-13 and Si-29 NMR with regard to a better correlation between structu re and material properties. Generally, a higher condensation degree of RSi( O-0.5)(3) units of GPTS is found after addition of metal oxide sols compare d to GPTS without additives. The metal oxide sols (10 mole% series) cause a n 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 hybri d 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 wi th increasing content of AlO/OH-species in silica sols. C-13 NMR studies re veal that the epoxide ring-opening does not completely lead to polyether st ructures but to considerable amounts (up to 40%) of ethylether groups which can influence the material properties (hardness).