Prepolymer

A prepolymer is a polymeric intermediate with reactive end groups that has not yet formed the final polymer network. It is typically an oligomer or short-chain polymer with defined functionality, produced with a degree of polymerization below that of the finished material. Prepolymers are designed to be reactive in a subsequent curing or chain-extension step to yield the final polymer.

Common end groups include isocyanate (NCO), hydroxyl, epoxide, amine, acrylate, or methacrylate functions. End groups are chosen to enable compatibility with other components and to control curing kinetics and network structure. Prepolymers are often made by partial polymerization or by reacting difunctional or multifunctional monomers in a controlled stoichiometry so that some reactive sites remain available for later crosslinking.

Preparation and handling hinge on control of molecular weight and functionality. For example, polyurethane prepolymers are typically formed by reacting di- or polyisocyanates with polyols to create NCO-terminated intermediates. Epoxy or acrylate prepolymers may be prepared by capping reactive chains with epoxide or acrylate end groups. Viscosity, pot life, and storage stability depend on the molecular weight and the nature of the end groups; moisture- or heat-sensitive groups require appropriate handling.

Applications rely on the ability of prepolymers to cure into a durable, crosslinked material. They are used in coatings, sealants, adhesives, elastomers, and foams, where controlled processing and tailored final properties are desirable. The choice of prepolymer chemistry influences adhesion, flexibility, hardness, and chemical resistance of the cured product. Safety considerations include handling reactive isocyanate-containing prepolymers and ensuring proper ventilation and moisture control.