Transparent thioether-ester-bridged polysilsesquioxane coating with enhanced water vapor barrier performance

Developing siloxane-based hybrid coatings with excellent water vapor barrier performance remains a great challenge. The water vapor barrier ability of siloxane-based coatings can be effectively improved by tailoring the chemical structure of silane precursors. In this article, three thioether-ester-bridged polysilsesquioxane (BPSQ) coatings were fabricated from bridged silsesquioxane precursors by sol-gel method involving hydrolysis and condensation reactions. The bridged silsesquioxane (BSQ) precursors were synthesized by (3-mercaptopropyl)trimethoxysilane (MPTMS) and reagents with molecular structure containing C C groups via a facile thiol-ene click reaction. Experimental evidence obtained from FT-IR and NMR techniques confirmed the bridged molecular structure of BSQ precursors. The results obtained from XRD, SEM and TEM proved that the BPSQ coatings had short range ordered and long range disordered lamellar structure parallel to the substrate. These lamellar BPSQ coatings performed better water vapor barrier ability with WVTR of 3 ~ 7 g·cm −2 ·d −1 in comparison to polymer and silica-based hybrid coatings. Of them, MA-BPSQ coating performed the best water vapor barrier ability. The chemical structure of bridged organic chain had great effect on the distance of lamellar nanostructure, which played a key role in improving water vapor barrier property of BPSQ coatings. • The BPSQ precursors are prepared through the facile thiol-ene click reaction. • The bridged organic chain length influenced the microstructure of BPSQ coatings. • The BPSQ coatings are transparent and flexible. • The BPSQ coatings perform good water vapor barrier ability.