A Novel Approach to Cure-on-Demand Coatings Using Ammonia to Catalyze Thiol-Acrylate and Thiol-Epoxy Reactions.

Cure-on-demand thiol-acrylate and thiol-epoxy coatings were developed by using ammonia as a catalyst. This novel method is a one-pot formulation that eliminates the need for volatile organic components and introduces a novel curing technique for coatings. Two ammonia sources were employed: a 30% aqueous solution of ammonia and ammonia generated by the urea-urease clock reaction with watermelon seed powder (WMSP) serving as a source of the urease enzyme. The pot lives were extended to at least 30 days by adding stabilizers. The use of the urea-urease clock reaction produced ammonia after a programmable delay, which allowed the coating to be covered with aluminum foil to prevent ammonia loss. The cure times for thiol-acrylate coatings were shorter, although their mechanical strengths were lower compared to thiol-epoxy coatings, which had longer cure times but superior mechanical properties.