1H MAS NMR study of structure of hybrid siloxane-based networks and the interaction with quartz filler

1H MAS NMR spectroscopy has been used to study the structure of hybrid siloxane networks prepared by acid-catalyzed polycondensation of tetraethoxysilane (TEOS), dimethyldiethoxysilane (DMDEOS) and methyltriethoxysilane (MTEOS) with or without quartz powder as a filler of resulting networks. Dynamic behavior and nature of silanol protons strongly depend on the amount of methyl groups in the hybrid network. It has been found that the resulting siloxane networks form very thin layers at the surface of the quartz grains. No free or highly mobile water or isolated silanols are present in these layers. The present water molecules and silanols are very strongly hydrogen-bonded to bridging oxygen of quartz particles. Such hydrogen bonds significantly contribute to mechanical strength of the filled network.