How are plastics made from polymers and monomers?

Plastics are manufactured through a chemical process known as polymerization, in which small molecules called monomers are chemically linked to form large, chainlike or network molecules called polymers. This process generally occurs through two primary mechanisms:1

• Addition polymerization: Monomers, typically those containing carbon-carbon double bonds, react to form a polymer chain without the creation of by-products. This is often facilitated by catalysts that control the structural arrangement of the molecules.123
• Condensation polymerization: This process involves the combination of monomers accompanied by the formation of simple by-products, such as water.14

Once the polymer is created, it can be processed into plastic objects through methods such as melting, shaping, and solidifying. Thermoplastic materials soften when heated, allowing them to be molded, while thermosetting resins form permanent, cross-linked three-dimensional networks that do not melt upon reheating. The specific properties of the resulting plastic—such as its strength, flexibility, or density—depend on the chemical structure of the monomers used and the specific polymerization technique employed.5136