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Polymerisation is the process in which two or more two monomers join together to form a polymer by different chemical reactions. Different long polymer chains or three-dimensional structures can be formed by this process. The process of polymerization occurs by different reaction mechanisms which are dependent on the functional group present on the monomer and also their non-bonding interactions. The process of polymerization is mainly of two types which consist of additional polymerization and condensation polymerization. The word “condensation polymerization” includes the release of water molecules in the process and as the product form lacks some molecules of water, it is known as condensation polymerization.
What is Condensation polymerization?
The process in which a larger structure can form by the step-growth process by joining small monomers by the release of water molecules is known as condensation polymerization. The process also refers to step-growth polymerization. But some of them can be considered an exception as they follow the process preset in the addition polymerization.
Condensation polymerization equation
n H2N-X-CO2H → [HN-X-C(O)]n + (n-1) H2O.
Claisen condensation polymerization
Claisen condensation polymerization occurs between two esters or one ester and another carbonyl compound consisting of carbon-carbon bond formation when a strong base is present in the reaction medium.
Characteristics of condensation polymerization
There are some characteristics of condensation polymerization are as follows-
- It is important in this type of polymerization, to have two functional groups in the monomer alcohol, carboxylic acids, or amine.
- The reaction in the process of condensation polymerization occurs between two different or similar functional groups. The reaction can join two monomers, one monomer and one dimer, one dimer and one oligomer, one dimer and one chain, and two different chains as well to form polymers.
- In this case, small monomers combine to form larger molecules in the form of long-chain or three-dimensional structures.
- In the case of condensation polymerization, mixed properties of functional groups or molecules are considered.
- When both the functional group are difunctional, a linear polymeric chain is formed in this process.
- If the functional groups are tri or tetra-functional, then polymers that are formed by the process of condensation polymerization generally have a three-dimensional structure because they will form a cross-linked polymeric structure.
- The average molecular weight decreases when monomers are added with one reactive group. Therefore, the functionality of each monomer determines the average molecular weight and cross-link density.
Difference between Addition and Condensation polymerization
Addition Polymerisation | Condensation Polymerisation |
It is necessary to have at least one double bond or triple bond in the process of addition polymerization. | It is necessary to have at least two different or identical functional groups in case of condensation polymerization. |
In this case, monomers join to form a single polymeric product. | In this case, monomers join to form polymeric products and some by-products as well such as water or methyl alcohol. |
The number of monomeric units decreases steadily throughout the reaction. | In this condensation polymerization, in the early stage, monomers disappear. |
In the case of addition polymerization, the molecular weight of the polymer can be expressed as the integrated multiple of the molecular weight of the monomer. | In the case of condensation polymerization, the molecular weight of the polymer cannot be expressed as the integrated multiple of the molecular weight of the monomer. |
At once, a polymer of huge molecular weight can be formed by this process | Molecular weight of the polymer increases with time in this condensation polymerization. |
If a huge amount of time is provided in the addition polymerization, then a better yield is possible but has no impact on the molecular weight. | Longer reaction times are essential to obtain high molecular weight. |
Thermoplastics are produced in this process. | Thermosetting plastics are produced in this process. |
Generally, homochain polymers are formed in this process. | Generally, heterochain polymer is formed in this process. |
Example of Condensation Polymerisation
Both polyester and nylon are formed in the process of condensation polymerization. The two monomers which produce the polyamide are adipic acid and hexamethylenediamine. In this process, the by-product that is formed is the water molecule.
HOOC–(CH2)n–COOH + HO–(CH2)m–OH → HOOC–(CH2)n–COO–(CH2)m–OH + H2O
Another example of condensation polymerization is the formation of polyester by two monomers that are dibasic acid and glycol. In this process, the by-product that is formed is the water molecule.
Conclusion
Polymerisation is the process in which two or more two monomers join together to form a polymer by different chemical reactions. Different long polymer chains or three-dimensional structures can be formed by this process. The process of polymerization is mainly of two types which consist of additional polymerization and condensation polymerization. The word “condensation polymerization” includes the release of water molecules in the process and as the product form lacks some molecules of water, it is known as condensation polymerization. The process in which a larger structure can form by the step-growth process by joining small monomers by the release of water molecules is known as condensation polymerization.
