Isocyanatepolyol

Isocyanatepolyol is not a widely standardized term in polyurethane chemistry, but it is commonly used to describe isocyanate-terminated prepolymers or related polymeric products formed from polyols and di- or polyisocyanates. In practical terms, it refers to a material in which residual isocyanate groups (-NCO) remain at the ends of a polyurethane chain that has been built from a polyol backbone. These prepolymers are designed to react further with additional isocyanate-free components (such as polyols or amines) to complete curing or to tailor final properties.

Preparation and structure

Isocyanate-terminated prepolymers are prepared by reacting a polyol (often a polyether or polyester polyol) with an excess amount of a diisocyanate or higher-functionality isocyanate. The reaction forms urethane linkages along the chain and leaves reactive NCO groups at the chain ends. The resulting product’s performance depends on the polyol type, the choice of isocyanate (for example MDI, TDI, or HDI), the NCO content, and the molecular weight distribution. NCO content is a key parameter used to predict reactivity and cure behavior.

Applications

Such isocyanate-terminated prepolymers are used as reactive chemicals in polyurethane formulations for coatings, adhesives, sealants, and flexible or rigid foams. They enable fast curing, adjustable pot life, and the ability to tailor mechanical properties, hardness, and thermal stability by varying the polyol backbone and the extent of isocyanate end groups.

Safety and handling

Isocyanates are hazardous and can cause respiratory sensitization and skin or eye irritation. Handling requires appropriate engineering controls, ventilation, and personal protective equipment. They are moisture sensitive and can release carbon dioxide upon exposure to moisture, so storage and processing should be moisture-controlled and performed in well-ventilated areas.

Note

The term isocyanatepolyol is informal; more precise terminology uses “isocyanate-terminated prepolymer” or “NCO-terminated prepolymer” to describe these materials.