Sol-Gel Networks: Fundamental Investigations of the Chemistry of Sol-Gel Silicate Glasses and Poly(Siloxane) Toughened Silicates

ABSTRACTThe low-temperature sol-gel process opens a number of new materials possibilities for generation of glasses with predetermined properties by the incorporation of organic modifiers into the network. Polysiloxanes are potentially interesting organic modifiers for toughening and possibly surface-modifying the silicate networks. Some fundamental studies of the hydrolysis and condensation processes in a tetramethylorthosilicate (TMOS) system, in the absence of added catalyst, have been conducted using 1H and 29Si NMR. The effects of some of the reaction parameters and processing conditions for the subsequent conversion of the gel to monolithic dried gels by heat treatment have been investigated by techniques such as thermal analysis and mass spectroscopy. Procedures which employ mild pressures have been established that permit the generation of monolithic products which show greatly reduced cracking tendencies. Finally, methoxy functionalized poly(dimethylsiloxane) oligomers that can react into the sol-gel network have been prepared. The intermediates are commercially accessible and the process is scaleable. Utilization of a catalyst-free system eliminates the tendency of the siloxane modifier to undergo undesired rearrangements that are known to occur in the presence of strong acids or bases.