isocyanateterminated

Isocyanateterminated, often written as isocyanate-terminated, describes a molecule or polymer chain whose reactive terminus is an isocyanate group (-NCO). Such termination provides sites for further reaction and crosslinking.

In polyurethane chemistry, isocyanate-terminated prepolymers are prepared by reacting a polyol with an excess of diisocyanate, yielding chains that retain one or more unreacted isocyanate groups at their ends. This end-capping allows subsequent curing with other components to form crosslinked networks.

Reactivity: The NCO group readily reacts with compounds containing active hydrogen, such as alcohols and amines, to form urethane and urea linkages, respectively. Reaction with water releases CO2 and amine, leading to foaming in some formulations.

Applications: Isocyanate-terminated materials are used as reactive polyurethanes for coatings, adhesives, sealants, elastomers, and foams. Common diisocyanates include MDI, TDI, and HDI; commercial isocyanate-terminated prepolymers are marketed for resins and coatings.

Safety: Isocyanates are hazardous and can cause sensitization, asthma, and skin/eye irritation. Handling requires appropriate engineering controls, personal protective equipment, and adequate ventilation.