Dynasylan 40 is a colorless, low-viscosity liquid with an SiO2 content of 40%. The polysilicic acids still have a sufficient content of ethoxy groups which can be activated by acid- or base-catalyzed hydrolysis. Condensation starts even during hydrolysis, with the formation of relatively large polymeric molecules. During storage of these hydrolysates, condensation continues until a gel is formed, where the rate depends on the degree of hydrolysis.
The action of the hydrolysates as binders is based on the continuation of the hydrolysis with subsequent gelation and dehydration to give polymeric SiO2 structures.
Dynasylan 40 is immiscible with water, so hydrolysis therefore requires a cosolvent as solubilizer.
Dynasylan 40 is formed in the presence of water from tetraethyl silicate (Si[OEt]4) by partial hydrolysis of the ethoxy groups to hydroxyl groups and subsequent condensation with formation of siloxane bonds (-Si-O-Si-).
Dynasylan 40 is also used as starting material for sol-gel processes.