Difference Between Propylene and Polypropylene

Main Difference – Propylene vs Polypropylene

Propylene is an organic compound and a hydrocarbon. It is the second simplest alkene in the alkene series. Propylene is unsaturated due to the presence of a double bond. At room temperature, it is gas. However, it is mainly used for the production of polypropylene, a polymer that is widely used all over the world for different purposes. Polypropylene is produced from propylene monomer polymerization. The main difference between propylene and polypropylene is that propylene is a simple molecule whereas polypropylene is a giant macromolecule.

Key Areas Covered

1. What is Propylene
– Definition, Uses, Manufacture
2. What is Polypropylene
– Definition, Tacticity, Uses
3. What is the Relationship Between Propylene and Polypropylene
4. What is the Difference Between Propylene and Polypropylene
– Comparison of Key Differences

Key Terms: Carbon, Cracking, Hybridization, Polymer, Polymerization, Polypropene, Polypropylene, Propene, Propylene, Tacticity

What is Propylene

Propylene is a hydrocarbon having the chemical formula C₃H₆. The IUPAC name of propylene is propene. It is the second simplest alkene having three carbon atoms bonded to each other. It is an unsaturated compound having a double bond. Therefore, there are two types of carbon-carbon bonds; C=C bond and C-C bond. Hence, this compound has two types of carbon atoms; two sp² hybridized carbon atoms and one sp³ hybridized carbon atom.

Difference Between Propylene and Polypropylene

Figure 1: Ball-and-Stick Structure of Propylene

The molar mass of propylene is 42.08 g/mol. It is a colorless gas at room temperature and has a petroleum-like odor. The melting point of propylene is −185.2 °C and the boiling point is −47.6 °C.

Use of Propylene for the Production of Other Chemicals

Polypropylene
Propenoic acid
Propenonitrile (acrylonitrile)
1-(ethylmethyl)benzene (cumene)
Epoxypropane
Butanol

Propylene Manufacturing

Propylene is produced from fossil fuels including petroleum oil, natural gas and coal. It is formed as a byproduct of crude oil refining and processing of natural gas. Propylene is produced mainly by two cracking methods:

Steam cracking (of naphtha)
Catalytic cracking (of gas oil)

These cracking reactions produce propylene along with many other products, as a mixture. Therefore, propylene is separated from this mixture by fractional distillation. However, catalytic cracking yields more propylene when compared to steam cracking.

What is Polypropylene

Polypropylene is a polymer made out of propylene monomers. It is also known as polypropene. The general formula for polypropylene is [CH(CH₃)CH₂]_n. Polypropylene is a thermoplastic polymer that has applications as both fibers and plastics. Polypropylene softens when heated and can be remoulded into different shapes, which is a characteristic property of thermoplastic polymers. Polypropylene is made from addition polymerization. The major application of this material is its use as a packaging material.

Main Difference - Propylene vs Polypropylene

Figure 2: Repeating Unit of Polypropylene

Polypropylene is cheap because it is one of the most recyclable plastics that are available. Unlike in the monomer, polypropylene has no double bonds in its polymer structure. Therefore, it is a saturated structure.

The tacticity of a polymer is the arrangement of the side groups/pendant groups (-CH₃) along the polymer chain. There are three types of tacticities that can be observed in polypropylene; Isotactic, Atactic and Syndiotactic. Isotactic polymer structure is composed of polymer chains containing the pendant group on the same side. Atactic polymer structure is composed of polymer chains containing methyl group in a random manner. In syndiotactic structure, the methyl groups are attached in an alternating pattern.

The most favorable properties of polypropylene include low density, good transparency, recyclability, and stretchability. Some common applications of polypropylene include the production of films for food packaging, textile industry (for the production of carpets, etc.), production consumer goods, etc.

Relationship between Propylene and Polypropylene

Polypropylene is produced from propylene via addition polymerization.

Definition

Propylene: Propylene is a hydrocarbon having the chemical formula C₃H₆.

Polypropylene: Polypropylene is a polymer made out of propylene monomers.

Composition

Propylene: Propylene is a simple individual molecule, an alkene.

Polypropylene: Polypropylene is a polymer containing a large number of repeating units.

Saturation

Propylene: Propylene is an unsaturated compound due to the presence of a double bond.

Polypropylene: Polypropylene is a saturated compound and there are double bonds or triple bonds.

Hybridization of Carbon Atoms

Propylene: Propylene has both sp² and sp³ hybridized carbon atoms.

Polypropylene: Polypropylene has only sp³ hybridized carbon atoms.

Molar Mass

Propylene: Molar mass of propylene is 42.08 g/mol.

Polypropylene: Polypropylene has a molar mass of 42.08 g/mol for one of its repeating unit.

Tacticity

Propylene: Tacticity is absent in propylene.

Polypropylene: Tacticity is present in polypropylene.

Major Uses

Propylene: Propylene is mainly used as a monomer for the production of polymers and other compounds such as propenoic acid, propenonitrile, etc.

Polypropylene: Polypropylene is used as films for food packaging, in the textile industry (for the production of carpets, etc.), production of consumer goods, etc.

Conclusion

Polypropylene is the polymer produced from the propylene monomer via addition polymerization. Propylene is capable of undergoing this polymerization due to the presence of a double bond, which makes propylene reactive. The main difference between propylene and polypropylene is that propylene is a simple molecule whereas polypropylene is a giant, macromolecule.

Reference:

1. Lazonby, John. “Propene (Propylene).” The Essential Chemical Industry online, Available here.
2. “Propene.” Wikipedia, Wikimedia Foundation, 23 Jan. 2018, Available here.

Image Courtesy:

1. “Propylene-3D-balls” By Ben Mills and Jynto – Derivative of File:Cis-but-2-ene-3D-balls.png (Public Domain) via Commons Wikimedia
2. “Polypropylene” By Ed (Edgar181) – Own work, Public Domain) via Commons Wikimedia