prepolimer

A prepolymer is a polymer intermediate characterized by a lower molecular weight than a fully cured polymer and by reactive end groups that enable further chemical reaction. Prepolymers are produced in a controlled partial polymerization or condensation, serving as building blocks for more complex materials. They are widely used across polymer chemistries, including polyurethanes, epoxies, silicones, and acrylates, to tailor viscosity, reactivity, and pot life before final curing.

In polyurethane technology, prepolymers are typically isocyanate-terminated, formed by reacting an excess of di- or polyisocyanate with polyols. The resulting material contains residual isocyanate groups (NCO) that can react with chain extenders, crosslinkers, or moisture to form polyurethane networks during cure. The molecular weight and NCO content of the prepolymer control cure rate, mechanical properties, and adhesion. While isocyanate-terminated prepolymers are common, other end-group chemistries can be used, depending on formulation.

Applications include coatings, adhesives, sealants, and elastomer formulations, as well as flexible foams and composite matrices. Prepolymers allow lower viscosity and easier processing, while enabling rapid curing and high-performance properties once formulated with compatible curatives and catalysts.

Safety and handling: many prepolymers used in polyurethane systems contain reactive isocyanate groups, which can cause sensitization and irritation. They are moisture-sensitive; exposure to water can trigger curing and release CO2. Storage typically requires dry, sealed containers and temperature control; proper ventilation and personal protective equipment are recommended.