What Is Polymerization? Types, Mechanism, and Examples

When talking about polypropylene or other polymer-based plastics, you may also hear about polymerization. Polymerization is a process in the industry that combines small molecules called monomers to form larger polymers.

This article discusses polymerization in chemical processes, including the types, examples, and mechanisms. Thus, read detailed information below!

What Is Polymerization?

Polymerization is the process of conjoining small molecules (monomers) into bigger polymer chains. Generally, polymerization is the process of obtaining polymers. This process is important to produce various synthetic materials, one of which is plastic.

To create polymerization products, you need at least 100 monomer combinations with specific characteristics, like solid or elastic. This condition differentiates polymers from other substances, which come from smaller molecules.

A polymer is also called a macromolecule. Usually, a polymer from polymerization has a linear or branched structure. The molecular chains can also be measured with polymerization degrees. It also has strong covalent bonds, creating a strong force of attraction.

The complexity of the polymerization reaction mechanism can vary depending on the functional groups (atom groups) in the reacting monomers. The simplest reaction involves the polymer creation from an alkene through a free-radical reaction. This kind of reaction is used to produce polyethylene.

Then, the polymerization process is divided by the number of monomers involved. If there is only one type of polymer, the process is called photopolymerization. Besides, if there is more than one type of monomer, the process is called copolymerization.

How Polymerization Happens

In general, polymerization occurs in three steps: initiation, propagation, and termination. Here is the brief explanation:

Initiation: A reaction emerges when the initiator releases a free radical, a catalyst, or an ion that breaks down the double bond of monomers.
Propagation: When a free radical reacts with monomers and creates reactive chains that can interact with other monomers.
Termination: The reaction halts because two free radicals meet and create covalent bonds.

One example of a material undergoing those steps is polyvinyl chloride.

Types of Polymerizations

According to the main polymerization reaction, the process is divided into two types, which are condensation and addition. Below is the explanation:

1. Condensation Polymerization

This polymerization forms a polymer by combining small molecules via a reaction involving functional groups, with or without the release of small molecules. Condensation also results in byproducts of water or hydrogen chloride.

One of the examples is nylon, which is among polyamides. Nylon has an amide bond and undergoes condensation polymerization, in which diamine and dicarboxylate meet and attach to make a long chain called polyamide.

2. Addition Polymerization

Addition happens when double-bonded monomers react and produce new double bonds. Some examples of addition polymerization are polystyrene, polyethylene, and polyacrylate.

Kinds of Polymers

Polymerization is a process of creating polymers. Polymers are categorized based on the source, polymerization reaction, force, and structure. The kinds of polymers are as follows:

1. Based on Structure

Based on the structure, the polymer is divided into three types: linear, branched, and cross-polymers. A linear polymer contains long and straight monomer chains. The example is polyvinyl chloride.

Besides, a branched polymer is a linear polymer with branches. The example is low-density polyethylene (LDPE). Lastly, a cross-polymer is a polymer with cross-linking bonds. The example is melamine.

2. Based on the Source

Based on the source, polymers are categorized into natural, semi-synthetic, and synthetic polymers. Natural polymers come from natural materials, such as rubber and resin.

On the other hand, semi-synthetic polymers come from modified natural polymers, like modified rubber. Lastly, synthetic polymers are completely man-made, like synthetic rubbers.

3. Based on Polymerization Reaction

As explained before, there are two polymerization reactions: addition and condensation. These differentiate the type of polymer as follows:

Addition polymer: Polymer made of repeated monomer addition with double or triple bonds. If the monomer added is similar, it is called a homopolymer. If it is distinct, it is called a copolymer.
Condensation polymer: Polymer formed by repeated condensation from tri- or bi-functional monomer units. Condensation polymerization releases water and hydrogen from the polymer.

4. Based on Force

Lastly, polymers are categorized by the force between the molecules. Here is the complete explanation:

Fiber: A polymer that has strong intermolecular forces, making it stay close to each other and almost compact. The examples are polyester and nylon.
Elastomer: A solid, rubber-like polymer. The polymer bonds tend to be weak, so the material can be stretched. The example is styrene-butadiene rubber (SBR).
Thermoset polymer: Cross-linked or multi-branched polymers. This polymer is easy to shape when heated, but cannot return to its initial shape, making it not reusable. The example is bakelite.
Thermoplastic polymer: A linear polymer that can be heated and shaped continuously, making it recyclable. The example is polystyrene.

Examples of Polymerization

As one of the plastic-making processes, you surely often encounter products undergoing this process. The examples of polymers you can see daily are as follows:

Olefin: Olefin is frequently found in petroleum and natural gas processing. The polymerization of olefins affects the characteristics of fuels.
Synthetic rubbers: Synthetic rubbers are made of styrene and butadiene monomers undergoing copolymerization.
Polyvinyl chloride: PVC undergoes polymerization and is categorized into two types, which are rigid PVC, like water pipes, and flexible PVC, like infusion tubes.
Synthetic fiber: Some examples of synthetic fibers are apparel materials, like nylon and polyester.
LDPE: A polymer formed from the ethylene polymerization process and then used to produce flexible pipes, toys, and squeeze bottles.

That is the information about polymerization you can learn. Polymer, as a product of polymerization, is one of the inevitable materials in daily life and industrial needs.

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