Vinyltriethoxysilane (A-151 / KH-151)

Vinyltriethoxysilane (VTES, A-151/KH-151) is a bifunctional organosilane coupling agent featuring a vinyl functional group (–CH=CH₂) that copolymerizes with unsaturated polyester and vinyl ester resins, and an ethoxysilane group (–Si(OEt)₃) that bonds to glass, silica, and other mineral surfaces through silanol condensation. This dual functionality makes VTES an effective primer and in-situ coupling agent for glass fiber composites and mineral-filled thermoset systems.

In glass fiber composites, vinyltriethoxysilane is applied as a sizing component on glass fibers to improve fiber-resin interfacial adhesion. The ethoxysilane end reacts with surface silanol groups (Si-OH) on glass, forming stable Si-O-Si bonds. The vinyl group co-reacts with the unsaturated polyester network during cure (via radical polymerization with styrene), creating a chemical bond across the glass-resin interface. This chemical coupling dramatically improves the retention of mechanical properties in wet and humid conditions, which is a critical performance requirement for marine and infrastructure FRP.

VTES is also used as a surface treatment for mineral fillers (ATH, silica, wollastonite) to improve their dispersibility and interfacial adhesion in UPR systems. Treatment can be done in-situ (added directly to filled resin during mixing) or pre-treatment of the dry filler. Dosage for filler treatment: 0.5–2.0% on filler weight. For glass fiber sizing: typically used in combination with film formers and lubricants.