Polypropylene (PP) is a thermoplastic polymer that belongs to the polyolefin family of plastics. It is made by the polymerization of propylene, which is a byproduct of the refining of natural gas and crude oil. PP is a type of copolymer with unique properties, such as high strength, durability, and chemical resistance. These are due to its linear polymer structure and the presence of methyl groups on the polymer chains.

The polymerization of PP takes place through a process called chain-growth polymerization. During this process, the propylene monomers are added to a catalyst, which initiates the formation of a polymer chain. The polymer chains then grow in length by the addition of more monomers, forming a long chain molecule. The properties of the final polymer depend on the conditions used during the polymerization process, such as temperature, pressure, and the type of catalyst used.

The history of Polypropylene (PP) in science can be traced back to the early 1950s when the Italian chemist Giulio Natta and his team at the Italian chemical company Montecatini, discovered a new catalyst that could be used to polymerize propylene, a byproduct of oil refining, into a new type of plastic. This new plastic was named polypropylene and it was the first thermoplastic polymer made from propylene. In the following years, further research was conducted on the synthesis, properties and processing techniques of PP, which led to the development of new catalysts that allowed for the production of isotactic PP, which is the most common form of PP used today. The first commercial production of PP started in the late 1950s and since then it has become one of the most widely used thermoplastic polymers due to its unique properties such as high strength, durability, and chemical resistance.

PP is a versatile material that can be easily molded, extruded, and thermoformed, making it suitable for a wide range of applications. Its properties make it a popular choice in the automotive, packaging, and consumer goods industries. Today, scientists continue to research new ways of improving the properties of PP by developing new catalysts, modifying the polymerization process, and blending PP with other polymers to enhance its properties and increase its versatility.