Blocked isocyanates are organic compounds that have their isocyanate functionality chemically blocked to control reactivity. They are the product of an isocyanate moiety (nearly always a di-isocyanate) and a suitable blocking agent. It may also be a polyurethane prepolymer that is NCO terminated but this functionality has also been chemically reacted with a blocking agent.
They are usually used in polyurethane applications but not always. They are extensively used in industrial applications such as coatings, sealants and adhesives.