Rapid curing of polysilazane coatings at room temperature via chloride-catalyzed hydrolysis/condensation reactions

Abstract

Moisture curing of polysilazane coatings at room temperature is of advantage to industrial applications, though it often takes a longer time than the other curing methods. To tackle this problem, tetrabutylammonium chloride (TBAC) is applied in this work as an efficient catalyst for the hydrolysis and condensation reactions of polymethyl(hydro)/polydimethylsilazane coatings under ambient conditions. In the suggested catalytic mechanism, the Si–H group is nucleophilically attacked by chloride ions to form a transient Si–Cl group, which is then nucleophilically substituted by a hydroxyl group from the moisture environment. It is found that by adding TBAC in the polysilazane coating, 1.6 times more of the reactive groups (Si–H, Si–NH) are consumed during the curing process in a shorter time (the dry-to-touch time for the uncatalyzed and the TBAC-catalyzed polysilazane coatings are ca. 19 h and 1 h, respectively), while 2 times more of the Si–O–Si groups are formed. Owing to the significantly enhanced crosslinking rate and degree, the coating quality and the mechanical properties are greatly improved. The hardness and the elastic modulus of the coating are increased by a factor of two and four, respectively.