Thiol- and sulfide-functional silanes — led by mercaptopropyltrimethoxysilane — for adhesion promotion and sulfur-reactive coupling in coatings, sealants, and rubber-modified systems.
Functional silanes carry a reactive organic group, such as a thiol or a sulfide, that bonds to organic polymers while the alkoxy end bonds to inorganic surfaces. Mercaptopropyltrimethoxysilane (CAS 4420-74-0) is the mercapto (thiol) silane in this family; its -SH group couples to sulfur-cured systems and promotes adhesion to metal and mineral surfaces in coatings and sealants. Specify a mercapto silane where you need a sulfur-reactive coupling site instead of the amine or epoxy functionality of the other silane families.
The thiol group is both the strength and the limitation. It reacts readily with sulfur and unsaturated resins, giving strong covalent coupling, but mercapto silanes carry a characteristic odor and can interact with some cure catalysts, so handling and order of addition matter. Dose to the filler surface area you actually need to treat instead of overloading the system; excess silane adds cost and can plasticize the matrix without improving adhesion.
A closely related material, bis-[3-(triethoxysilyl)propyl] disulfide (often sold as Si-75), is a sulfide-functional silane used mainly as a coupling agent in silica-reinforced tire and rubber compounds. The catalog tags it for Plastics & Polymers and Industrial Manufacturing rather than coatings, so it is surfaced on those industry pages instead of this one. For coatings and sealant adhesion, the mercapto silane above is the grounded choice.
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