Isobutyltrimethoxysilane (iBTMOS / Dynasylan IBTMO type)

Isobutyltrimethoxysilane (iBTMOS) is an alkylsilane surface modifier combining the fast methoxy hydrolysis of MTMS with the enhanced hydrophobicity and deeper substrate penetration of a branched C4 alkyl chain. The isobutyl group is slightly bulkier than n-propyl but significantly less bulky than octyl, giving iBTMOS a practical balance: high water-repellency (surface contact angle >105° on treated mineral surfaces), good substrate penetration, and low yellowing risk — unlike long-chain alkylsilanes (C16, C18) which can cause whitening on porous substrates.

iBTMOS is the preferred silane for hydrophobic treatment of calcium carbonate (CaCO3) used in waterborne architectural paints, where it dramatically reduces water absorption without reducing TiO2 spacing efficiency. Treated CaCO3 at 0.3–0.8 wt% iBTMOS remains compatible with waterborne acrylic binders but delivers a scrub-resistant, hydrophobic filler surface that improves wet scrub resistance of exterior architectural coatings by 30–60% compared to untreated filler.

For concrete and masonry waterproofing, iBTMOS is widely used in formulated creams, gels, and impregnation fluids. Its branched C4 chain penetrates concrete pores more effectively than octylsilane while delivering superior water repellency compared to MTMS alone. Applied at 5–15% concentration in aqueous micro-emulsion or neat in solvent, iBTMOS-treated concrete achieves water absorption (W24 test, DIN EN 1062-3) typically <0.1 kg/m²·h^0.5 and chloride migration coefficients reduced by 70–90%.

iBTMOS is also used to hydrophobize fumed silica and precipitated silica for polyolefin compounding and rubber applications, and as a co-modifier with aminosilanes to tune the polarity balance of glass fiber sizings for polyolefin-matrix composites.