Mechanical properties and thermal stability of ambient-cured thick polysiloxane coatings prepared by a sol–gel process of organoalkoxysilanes

Abstract

Ambient-curable polysiloxane coatings were prepared by pre-hydrolysis/condensation of phenyltrimethoxysilane (PTMS) and dimethyldimethoxysilane (DMDMS) in the presence of ammonia solution and subsequently mixing with aminopropyltriethoxysilane (APS). The mechanical properties of coatings were thoroughly examined at both macro- and micro-level and the thermal stability of coatings was characterized by thermogravimetic analysis, both of which were correlated with coating composition and the hydrolysis/condensation degree of polysiloxane oligomer. It was found that pro-hydrolysis step is essential for fabrication of thick crack-free coatings (18–35μm). Higher DMDMS molar ratio, more APS dosage and lower hydrolysis/condensation degree of polysiloxane oligomer favor enhancing the hardness. Excellent impact resistance (50cmkg) of coatings was obtained at 5% and 10% APS dosage, despite of the type and structure of polysiloxane oligomer. Whatever, the best scratch resistance of coatings was attained using the polysiloxane oligomer, prepared at PTMS-to-DMDMS molar ratio of 2:8 and water-to-precursor molar ratio of 1:1, and 5% APS dosage. The polysiloxane coatings exhibit high thermal stability, however, which strongly depends on the coating composition.