Plastics are synthetic or semi-synthetic solid materials composed of long polymer chains, which are typically derived from fossil fuels or biomass. These materials are formed through polymerization, a chemical process where many small repeating units, called monomers, are joined together to create large, long-chain molecules. The resulting properties of plastic can be manipulated by adjusting the chemical structure, molecular weight, and physical additives, allowing for a vast range of materials from rigid, load-bearing structures to flexible films. The development of plastic science has revolutionized manufacturing across various sectors, enabling lightweight, durable, and moldable alternatives to traditional materials like metal and glass. Understanding the chemistry of these polymers, including terms like thermoplastic and thermosetting plastics, is central to material science and chemical engineering.