Effect of Prehydrolysis VTMS on the Structure–Property of Silane‐Terminated Polyurethane

Abstract

ABSTRACTSilane‐terminated Polyurethane (SPU) is in high demand in the sealant and adhesive industries because of its exceptional cohesive strength and excellent adhesive properties. To close a self‐curable SPU resin was synthesized using a two‐step solution polymerization process for 12 h at pH 2.8 using the sol–gel method. Subsequently, the polyurethane prepolymer's NCO moiety was terminated by VTMS silanol to prepare SPU resin. FTIR and liquid state NMR were used to study VTMS hydrolysis in an acidic medium. Explored the effects of VTMS on SPU properties, including crystallinity, Mn and Mw, viscosity, gel fraction, thermal, surface, and mechanical. FTIR and NMR (1H and 13C) spectra confirmed the successful termination of the prepolymer's unreacted diisocyanate with the hydroxyl moiety of silanol. XPS and FTIR were used to analyze the chemical structures of urethane, urea, siloxane, and the hydrogen bonds between SPU moiety. Increased wt% of silanol exhibits increased gel fraction (80%–91%) with a decreased degree of swelling (76%–45%) showing the formation of a cross‐linked structure. Including siloxane in polyurethane showed a synergetic effect, resulting in enhanced thermal stability through reduction of weight loss. The SPU exhibited a three‐stage degradation pattern, accompanied by decreased glass transition temperature and crystallinity. Siloxane enrichment increased SPU surface roughness (Rq‐218 and Ra‐69 nm) and hydrophobicity (94°–103°). Silane wt% increase causes significant changes in Young's (2.19–51 N/mm2) modulus, strain %, and adhesive strength (4.60–5.62 MPa). Silane‐terminated polyurethane can be used successfully as an adhesive and sealant.