Final answer:
A sealant polymerized by chemical reactions is known as a reaction polymer, with polyurethanes being a common example, where an isocyanate reacts with a polyol to form the polymer.
Step-by-step explanation:
A sealant that is polymerized by chemical reactions is commonly referred to as a reaction polymer. These polymers, such as polyurethanes, epoxies, and phenolics, are formed when small molecules or monomers chemically react to become a large single molecule, known as a polymer. In the case of polyurethanes, an isocyanate reacts with a polyol in the presence of a catalyst or when activated by ultraviolet light to form the long-chain polymer. Polymerization can occur through various mechanisms, including addition reactions where monomers add to one another without the loss of any atom, or condensation reactions where monomers join and release small molecules such as water in the process.