Polyethylene

This is the most common plastic used in the world today. Polyethylene is a polymer made of ethylene. Ethylene has two carbon atoms bonded to each other with a double bond. Two hydrogen atoms are bonded to each carbon. When polymerizing, the double bond is broken, and new sigma bond between two carbons of two ethylene molecules takes place. In other words, polyethylene is produced by an addition reaction of the monomer ethylene. Its repeating unit is –CH2– CH2-. Thus, this has a very simple structure with long chain carbon atoms. Depending on the way it is polymerized, the properties of the synthesized polyethylene change. Sometimes they can be straight chain, or sometimes they can be branched. Branched polyethylene is easy to make and lot cheaper. However, its strength is much lower than straight chain polyethylene. Polyethylene is used in making bottles, bags, toys, etc.

Polypropylene

Polypropylene is also a plastic polymer. Its monomer is propylene, which has three carbons and one double bond between two of those carbon atoms. Polypropylene is manufactured from propylene gas in the presence of a catalyst such as titanium chloride. It is easy to produce and can be manufactured with high purity. Polypropylenes are light in weight. They have a high resistance to cracking, acids, organic solvents and electrolytes. They also have high melting point and good dielectric properties and are non-toxic. Polypropylenes have a high economical value. They are used for pipes, containers, house ware, packaging, and automotive parts.