A polymer is a large molecule composed of repeating structural units called monomers, which are covalently bonded together. Polymers can be natural, like DNA and proteins, or synthetic, like plastics and rubber.

Polymers can be broadly classified into two types:

Natural Polymers: Found in nature, such as cellulose, proteins, and DNA.
Synthetic Polymers: Man-made, including materials like polyethylene, polystyrene, and nylon.

Polymerization is the chemical process through which monomers are chemically bonded to form a polymer. There are two main types of polymerization:

Addition Polymerization: Monomers with double bonds react to form a polymer without the loss of any small molecules.
Condensation Polymerization: Monomers with two or more reactive groups combine, releasing small molecules like water or methanol.

Addition Polymerization: Involves monomers with unsaturated bonds (e.g., alkenes). The polymer grows by successive addition of monomers, with no by-products.
Condensation Polymerization: Involves monomers with two or more functional groups. The polymerization process releases small molecules, such as water or alcohol, as by-products.

Thermoplastics: These polymers can be melted and re-molded multiple times. Examples include polyethylene and polystyrene.
Thermosetting Polymers: These polymers harden irreversibly after being heated and molded once. They cannot be re-melted or re-molded. Examples include epoxy and phenolic resins.

Polymers have a wide range of applications:

Packaging: Plastics like polyethylene and polypropylene.
Medical Devices: Polymers like silicone and polycarbonate.
Textiles: Fibers such as nylon, polyester, and spandex.
Construction: Polymers like PVC and acrylic are used in pipes and windows.