Solid state 29Si NMR investigation of inorganic-organic polymers with defined silicic acid units

By thermal analysis and 29Si NMR spectroscopy the thermal behaviour and structural changes of two different types of inorganic-organic polymers with defined double four-ring silicic acid units (Si8O20) were characterized. Polymer 1, prepared from the organic silicic acid precursors [(CH3)2HSi]8Si8O20 (Q8M8H) and [CH2=CH(CH3)2Si]8Si8O20 (Q8M8V), preserves the double four-ring structure up to 350°C Higher temperatures lead to structural reorganizations of the SiO4 tetrahedra forming at 900°C a structure similiar to amorphous silica. Polymer 2, synthesized by condensation reaction of the new organic silicic acid precursor [CH3O)3Si(CH2)3OC(O)CH(CH3)CH2Si(CH3)2]8Si8O20, shows with 37% uncondensed SiOH groups a remarkable high content of silanol groups caused by sterical hindrances