How does polymerization occur during the curing of some adhesives?

During the curing of many adhesives, polymerization occurs as a chemical reaction that transforms simple molecules, known as monomers, into large, chainlike or network polymers. This process creates stable covalent chemical bonds between the monomers, which provides the adhesive with the strength and flexibility required to bond surfaces effectively.12

Polymerization generally follows one of two pathways:
* Addition polymerization: Monomers react to form a polymer without creating by-products. This often requires catalysts or initiators to trigger the reaction. For example, in ultraviolet-cured adhesives, photoinitiators break down into free radicals upon exposure to light, inducing rapid polymerization.234
* Condensation polymerization: Each step of the reaction is accompanied by the formation of a simple by-product, such as water.2

Curing may also involve cross-linking, where network structures are formed to create permanent, heat-resistant bonds. This is common in thermosetting adhesives, where specific catalysts are often used to accelerate the reaction and ensure the adhesive sets within a reasonable timeframe.25