The key difference between addition polymerization and condensation polymerization is that for addition polymerization, monomer should be an unsaturated molecule whereas for condensation polymerization, monomers are saturated molecules.
Polymers are large molecules that have the same structural unit repeating over and over. The repeating units represent monomers. These monomers bind with each other via covalent bonds to form a polymer. They have a high molecular weight and consist over 10,000 atoms. In the synthesis process (polymerization), longer polymer chains form. There are two main types of polymers depending on their synthesis methods. If the monomers have double bonds between carbons, addition polymers form via addition polymerization. In some of the polymerization reactions, when two monomers combine, a small molecule releases, i.e. water. Such polymers are condensation polymers. Polymers have very different physical and chemical properties than their monomers.
CONTENTS
1. Overview and Key Difference
2. What is Addition Polymerization
3. What is Condensation Polymerization
4. Side by Side Comparison – Addition Polymerization vs Condensation Polymerization in Tabular Form
5. Summary
What is Addition Polymerization?
The process of synthesizing addition polymers is addition polymerization. This is a chain reaction; therefore, any number of monomers can join into a polymer. There are three steps to a chain reaction;
- Initiation
- Propagation
- Termination
Figure 01: Addition polymerization for polyethylene production (X is peroxide radical)
For an example, we will take the synthesis of polyethylene, which is an addition polymer useful in making products such as garbage bags, food wrap, jugs, etc. The monomer for polyethylene is ethene (CH2=CH2). Its repeating unit is –CH2-. In the initiation step, a peroxide radical generates. This radical attacks the monomer to activate it and produce a monomer radical. During the propagation phase, the chain grows. Activated monomer attacks another double bonded monomer and attaches together. Ultimately the reaction stops when two radicals join together and form a stable bond. Chemists can control the length of the polymer chain, reaction times and other factors to obtain the required polymer.
What is Condensation Polymerization?
Any condensation process that results in the formation of polymers, is the condensation polymerization. A small molecule like water or HCl releases as a by-product during the condensation polymerization. The monomer should have functional groups in ends, which can react together to continue the polymerization. For example, if the joining ends of two molecules have a –OH group and a –COOH group, a water molecule will release and an ester bond forms. Polyester is an example for a condensation polymer. In the synthesis of polypeptides, nucleic acids or polysaccharides, condensation polymerization takes place within biological systems.
What is the Difference Between Addition Polymerization and Condensation Polymerization?
The process of synthesizing addition polymers is addition polymerization. Any condensation process, which results in the formation of polymers, is the condensation polymerization. Therefore, addition polymerization is the reaction between monomers with multiple bonds, where they join together to form saturated polymers. And in condensation reactions, functional groups of two monomers react together releasing a small molecule to form a polymer.
The monomer should be an unsaturated molecule in addition polymerization whereas monomers are saturated molecules in condensation polymerization. Comparatively, addition polymerization is a rapid process when condensation polymerization is rather a slow process. As the end product, addition polymerization produces high molecular weight polymers, and they are non-biodegradable and difficult to recycle. The condensation polymerization produces low molecular weight polymers as its end products, and they are biodegradable and easy to recycle compared to addition polymers.
Summary – Addition Polymerization vs Condensation Polymerization
Addition and condensation polymerization are the two major processes of producing a polymer compound. There are many differences between the two processes. The difference between addition and condensation polymerization is that for addition polymerization, monomer should be an unsaturated molecule whereas for condensation polymerization, monomers are saturated molecules.
Reference:
1. “Addition Polymer.” Wikipedia, Wikimedia Foundation, 21 Mar. 2018. Available here
2. Libretexts. “Condensation Polymers.” Chemistry LibreTexts, Libretexts, 6 Sept. 2017. Available here
Image Courtesy:
1.’Polymerisation PE generique’ By Cdang – Own work, (Public Domain) via Commons Wikimedia