Hydrolysis reaction
Organosilane coupling agent molecules generally contain hydrolyzable functional groups, such as methoxy (- OCH ∝), ethoxy (- OC ₂ H ₅), etc. In the preparation environment of the sol gel method, when encountering water, these hydrolyzable groups will undergo hydrolysis reaction. For example, take silane coupling agent containing methoxy group as an example, its hydrolysis reaction formula is roughly as follows:
In the formula, R represents the organic functional group portion. Through hydrolysis reaction, silane coupling agent molecules generate active silanol groups (- Si (OH) ∝), which can participate in subsequent condensation reactions and become key active sites for constructing cross-linked structures.
Condensation reaction
The generated silicon hydroxyl (- Si (OH) ≮) can undergo polycondensation reaction with the silicon hydroxyl generated by the hydrolysis of the original metal alkoxides in the sol system or other hydroxyl containing substances (such as the existing hydroxyl in the gel network). The condensation reaction process can have the following two typical situations:
Self aggregation to form cross-linking: The silicon hydroxyl groups produced by the hydrolysis of silane coupling agents undergo mutual aggregation, and the reaction equation can be expressed as:
Through such self polycondensation, multiple silane coupling agent molecules are connected together to form a cross-linked chain segment with a certain branch structure, which expands in the gel system and enhances the cross-linking degree of the gel network.
Polycondensation with substances in the sol system to form cross-linking: The silanol groups hydrolyzed by silane coupling agents will also undergo condensation reactions with other hydrolysis products in the sol, such as silanol produced by the hydrolysis of metal alkoxides. For example:
(Here M stands for metal element). Through this condensation with other hydroxyl containing substances in the sol system, the organic silane coupling agent connects the originally relatively independent sol hydrolysis products and weaves them into the network structure of the gel, making the entire gel network more compact and cross-linked, thus improving the ability of the gel and the subsequent coating to resist deformation such as drying shrinkage, and enhancing the stability and integrity of the coating.
bridging effect 
Organic silane coupling agent molecules not only contain hydrolyzable siloxy groups, but also organic functional groups such as amino groups, vinyl groups, epoxy groups, etc. These organic functional groups can undergo chemical reactions with organic components in the coating system (such as added organic resins), such as ring opening addition reactions between amino groups and epoxy groups, or interact with each other through physical adsorption. In this way, the organic silane coupling agent acts as a "bridge", connecting the inorganic gel network with the organic components, further improving the cross-linking structure of the entire coating system, improving the comprehensive performance of the coating, and better dealing with possible problems such as drying shrinkage.
In a word, organosilane coupling agents effectively build and strengthen the cross-linking system in the sol-gel method through hydrolysis, polycondensation and bridging, and play an important role in improving the quality of the coating.

Room termperature curing polysilazane, pls check IOTA 9150, IOTA 9150K. 
High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.