Difference Between Polystyrene and Polypropylene

Polystyrene vs Polypropylene

Polymers are large molecules, which has the same structural unit repeating over and over.  The repeating units are called monomers. These monomers are bonded to each other with covalent bonds to form a polymer. They have a high molecular weight and consist over 10,000 atoms.  In the synthesis process, which is known as polymerization, longer polymer chains are obtained. There are two main types of polymers depending on their synthesis methods. If the monomers have double bonds between carbons, from addition reactions polymers can be synthesized. These polymers are known as addition polymers. In some of the polymerization reactions, when two monomers are joined, a small molecule like water is removed. Such polymers are condensation polymers.  Polymers have very different physical and chemical properties than their monomer. Moreover, according to the number of repeating units in the polymer, properties differ. There are a large number of polymers present in the natural environment, and they play very important roles.  Synthetic polymers are also used widely for different purposes. Polyethylene, polypropylene, PVC, nylon, and Bakelite are some of the synthetic polymers. When producing synthetic polymers, the process should be highly controlled to get the desired product always. Polypropylene has become a very controversial issue at the present day, due to their incapability of degradation. They make up a considerable percentage in our garbage; therefore, they keep on increasing on the earth surface. This problem has caught the attention of researchers, and recycled plastics have been synthesized.


Polystyrene is made up of the monomer styrene. It is also known as poly(1-phenylethene-1,2-diyl), and it is an aromatic polymer. The long hydrocarbon chain has phenyl groups attached to every other carbon atom in polystyrene. Polystyrene is a vinyl polymer, and it is synthesized by free radical vinyl polymerization. It can be a thermoset or thermoplastic. This is a hard and rigid material. Polystyrene is used to make toys, kitchen appliances, disposable drinking cups, packaging material, computer housing parts, etc. polystyrene can be recycled. Though, it is a highly used plastic all over the world, it causes less environment harm due to recycling.


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. Polypropylene are light in weight, has a high resistance to cracking, acids, organic solvents, electrolytes, has a high melting point, non-toxic and has good dielectric properties. Polypropylenes have a high economical value. They are used for pipes, containers, house ware, and packaging and for automotive parts.


What is the difference between Polystyrene and Polypropylene?

• The monomer for polystyrene is styrene, and the monomer for polypropylene is propylene.

• Polystyrene monomer has an attached phenyl group, whereas polypropylene monomer has a methyl group.

• Polystyrene is an aromatic polymer, because it has phenyl groups attached to every other carbon atom, but polypropylene is an aliphatic polymer.

• Polypropylene cannot be recycled, but polystyrene can be recycled.

• Polypropylene is a thermoplastic whereas polystyrene can be a thermoplastic or thermoset.