This document discusses polymers and plastics. It defines polymers as long-chain molecules formed by linking repeating molecular units (monomers) through polymerization. The earliest synthetic polymer was Bakelite, developed in 1906. Modern plastics started in the 1920s using raw materials from coal and oil. Polymers can be thermoplastics, which soften when heated and harden when cooled, allowing reshaping, or thermoset plastics, which permanently cure into shape upon heating. Common polymers include polyethylene, polycarbonate, and nylon, each with different properties and applications ranging from bottles to gears. Additives are added to polymers to modify properties like strength, color, and weather resistance.