3-Isocyanatopropyltriethoxysilane

3-Isocyanatopropyltriethoxysilane is a highly reactive bifunctional silane coupling agent containing an isocyanate (–NCO) group that reacts rapidly with hydroxyl (–OH), amine (–NH₂, –NH), and thiol (–SH) groups without need for a catalyst or elevated temperature. This makes it uniquely effective for coupling inorganic substrates to polyurethane (PU), polyurea, and hydroxyl-functional polymer systems where no other commercial silane provides such direct, fast reactivity.

In polyurethane composites and adhesives, isocyanatopropylsilane simultaneously anchors to glass, metal, or mineral filler through triethoxysilyl condensation and reacts with the PU matrix –OH or –NH groups through isocyanate addition. This creates an extremely robust dual-bond interface that is highly resistant to hydrolytic attack in humid or wet service conditions. The combination makes it the preferred silane for glass fiber sizing in glass fiber reinforced polyurethane RIM and SRIM composites, and for mineral filler treatment in PU casting and potting compounds.

Caution: the –NCO group is highly reactive and moisture sensitive. Contact with atmospheric humidity causes rapid formation of substituted urea and CO₂ release, reducing effectiveness and potentially causing foaming. All operations must be conducted under strictly dry conditions with moisture-free solvents, substrates, and mixing equipment. Storage life is short (6–12 months) even in sealed containers. The –NCO group is also acutely toxic by inhalation at low concentrations (OSHA PEL 0.02 ppm); strict respiratory protection is mandatory during handling.