The key difference between free radical and ionic polymerization is that free radical polymerization occurs through radicals that contain an unpaired electron whereas ionic polymerization occurs via ionic species that has no unpaired electrons.
Polymerization is the chemical process of forming polymer materials. A polymer is formed from the combination of a large number of monomer units via chemical bonds. There are three major forms of polymerization as addition, condensation, and radical polymerization.
CONTENTS
1. Overview and Key Difference
2. What is Free Radical Polymerization
3. What is Ionic Polymerization
4. Side by Side Comparison – Free Radical vs Ionic Polymerization in Tabular Form
5. Summary
What is Free Radical Polymerization?
Free radical polymerization is the process of forming a polymer material via the addition of free radicals. Free radicals can be formed in several ways. The most common method often involves an initiator molecule forming a radical. A polymer chain forms from the addition of the radical produced with the non-radical monomers.
Figure 01: Formation of PVC polymer from Free Radical Polymerization
There are three main steps involved in the radical polymerization process:
- Initiation
- Propagation
- Termination
The initiation step creates a reactive point. It is the point where the polymer chain forms. The second step is the propagation step in which the polymer spends its time in growing the polymer chain. In the termination step, the growth of the polymer chain stops. That can happen in several ways:
- Combination of the ends of two growing polymer chains
- Combination of the growing end of a polymer chain with an initiator
- Radical disproportionation (removal of a hydrogen atom, forming an unsaturated group)
What is Ionic Polymerization?
Ionic polymerization is the process of forming a polymer material using ionic chemical species as initial reactants. This is a subtype of chain-growth polymerization; there are two types of chain-growth polymerization as ionic and radical polymerization. Moreover, ionic polymerization can be divided further into two groups as cationic and anionic polymerization.
Figure 02: General Process of Ionic Polymerization
Anionic polymerization begins with an anion. Different types of initiators can be used in this type of polymerization process. There are three major steps that take place during anionic polymerization process: initiation, propagation and termination. The process is initiated by nucleophilic addition of an anion to a double bond in the monomer.
Cationic polymerization begins with a cation. The cation transfers its electrical charge to the monomer to activate the monomer for polymerization. The reactive monomer then becomes a cation, and the same step is repeated until the termination, forming a polymer material.
What is the Difference Between Free Radical and Ionic Polymerization?
Free radical and ionic polymerization are two different processes of forming a polymer material. These two are the subtypes of chain-growth polymerization. The key difference between free radical and ionic polymerization is that free radical polymerization occurs through radicals which contain an unpaired electron whereas ionic polymerization occurs via ionic species which has no unpaired electrons.
Moreover, in free radical polymerization, the radical makes the monomer a reactive radical while in ionic polymerization, the anion or cation binds with the monomer, making a reactive charged species.
Below is a summary of the difference between free radical and ionic polymerization in tabular form.
Summary – Free Radical vs Ionic Polymerization
Free radical and ionic polymerization are two different processes of forming a polymer material. These two are the subtypes of chain-growth polymerization. The key difference between free radical and ionic polymerization is that free radical polymerization occurs through radicals which contain an unpaired electron whereas ionic polymerization occurs via ionic species which has no unpaired electrons.