Polypropylene is produced by polymerization of together with complex organometallic catalysts at low and medium pressure. PP is a crystallizing polymer, the content of the crystalline phase is 73-75%. Like other polyolefins, PP is a nonpolar polymer. The surface of PP is "energetically low", which makes it impossible to connect different parts of the PP with the help of glue. Welding is used in order to connect PP parts. It is durable, elastic and unusually resistant to concentrated chemical solvents, acids and alkalis.