The key difference between addition and radical polymerization is that the addition polymerization occurs via the addition of unsaturated monomers whereas the radical polymerization occurs via the addition of free radicals.
Polymerization is the process of producing a polymer using a large number of monomers. There are two main types of polymerization processes; they are, addition polymerization, condensation polymerization. The radical polymerization is a form of addition polymerization.
CONTENTS
1. Overview and Key Difference
2. What is Addition Polymerization
3. What is Radical Polymerization
4. Similarities Between Addition and Radical Polymerization
5. Side by Side Comparison – Addition vs Radical Polymerization in Tabular Form
6. Summary
What is Addition Polymerization?
It is the process of forming an addition polymer via linking unsaturated monomers. The most common form of addition polymers is polyolefin polymers. Polyolefin polymers form when olefin monomers link with each other. Olefins are small unsaturated compounds such as alkene. Therefore, when these olefins undergo polymerization, the unsaturated bonds of these monomers convert into saturated bonds. However, the monomer of addition polymerization can be a radical, a cation or an anion.
Figure 1: Schematic Structure of Polypropylene, which is a Polyolefin Polymer
Synthesis of Addition Polymers:
There are three main forms of addition polymerization. Each polymerization initiates with a particular initiator, which leads to the polymerization process.
- Radical polymerization involves the polymerization of monomers in the presence of a radical which can attack a monomer to make a carbon radical.
- The initiator of a cationic polymerization process is an acid that can make a carbocation
- The initiator of an anionic polymerization process is a nucleophile that can make a carbanion
Some examples for addition polymers are as follows:
- LDPE (low density polyethylene)
- HDPE (high density polyethylene)
- PVC (polyvinyl chloride)
- Polypropylene
- Polystyrene
What is Radical Polymerization?
It is the process of forming a polymer material via the addition of free radicals. The formation of radicals can occur in several ways. However, it often involves an initiator molecule forming a radical. A polymer chain forms by the addition of the radical produced with the non-radical monomers.
Figure 2: Nitroxide Mediated Free Radical Polymerization for PVC
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 from 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 are the Similarities Between Addition and Radical Polymerization?
- Both are forms of addition polymerization process
- Both polymerizations involve three steps: initiation, propagation and termination of polymer chain growth.
What is the Difference Between Addition and Radical Polymerization?
Addition vs Radical Polymerization |
|
| Addition polymerization is the process of forming an addition polymer via linking unsaturated monomers. | Radical polymerization is the process of forming a polymer material via the addition of free radicals. |
| Nature of Monomers Used | |
| Olefins or unsaturated compounds usually having double bond | Free radicals having unpaired electrons |
| Bonding in Monomers | |
| Double bonds in monomers become saturated after the completion of polymerization | Unpaired electrons in the radicals become paired after the completion of the polymerization |
| Reactivity of Monomers | |
| Monomers undergo addition polymerization when the double bond converts to a single bond | Monomers undergo radical polymerization due to the high reactivity of the free radicals. |
Summary – Addition vs Radical Polymerization
Addition and radical polymerization are two common polymerization techniques. Radical polymerization is a form of addition polymerization. The key difference between addition and radical polymerization is that addition polymerization occurs via the addition of unsaturated monomers whereas radical polymerization occurs via the addition of free radicals.
Reference:
1. “Addition Polymer.” Wikipedia, Wikimedia Foundation, 21 Mar. 2018, Available here.
2. “Synthesis of Addition Polymers.” Chemistry LibreTexts, 21 July 2016, Available here.
3. “Radical Polymerization.” Wikipedia, Wikimedia Foundation, 3 Apr. 2018, Available here.
Image Courtesy:
1. “Mechanism of nitroxide mediated free radical polymerization for PVC” By Thilini ukwaththage – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Polypropylene isotactic mini trp” By PakpongICCH444 – Own work (CC BY-SA 4.0) via Commons Wikimedia