Aqueous-based polyurethane with dual-functional curing agent

Aqueous-based polyurethane (PU) with a carboxyl pendent group was prepared from a conventional PU prepolymer process. Its carboxyl group served as the ionic center for stabilizing the aqueous PU dispersion and as the curing s ite for post-curing reaction. A curing agent was synthesized from the subst itution reaction of phosphorus oxychloride or phenylphosphonic dichloride b y aziridine. Each compound consisted of two aziridinyl groups and the phosp horus composition. Its aziridinyl group reacted with a PU carboxyl group an d its phosphorus content was introduced to this PU curing system simultaneo usly. Those compounds served as both curing agent and flame retardant for t he PU curing system. The physical and mechanical properties of the resultin g PU were improved corresponding to the curing dosage. The thermal properti es and the flame inhibition behaviors of those post-cured PUs were evaluate d by measurements using thermogravimetric analysis, dynamic mechanical ther mal analysis, a limiting oxygen index, and a cone calorimeter.