Before learning about condensation polymerization let us quickly recall what polymerization is. Generally, polymerization is defined as a process in which two or more monomers engage in a chemical reaction and form long polymer chains or three-dimensional networks. Polymerization usually occurs via different reaction mechanisms which are affected by factors like the functional groups of the reacting compounds and their nonbonding interactions.
In any case, there are mainly two types of polymerization which are addition polymerization and condensation polymerization. However, we will study about the latter in this page.
What is Condensation Polymerization?
When we talk about condensation polymerization, it is a form of a step-growth polymerization where smaller molecules or monomers react with each other to form larger structural units (usually polymers) while releasing byproducts such as water or methanol molecule. The byproducts are normally referred to as condensate.
This polymerization is also sometimes referred to step-growth polymerization. However, in this context there are few exceptions that need to be considered. There are instances where molecules of some substances react as condensation polymerization but they follow the chain growth pattern as seen in additional polymerization.
Characteristics of Condensation Polymerization
Some of the main characteristics of this type of polymerization are;
- The molecules should have one or two functional groups (like alcohol, amine, or carboxylic acid groups)..
- The reaction occurs between two similar or different functional groups or monomers. It can take place between a dimer and oligomer, one monomer and one dimeror or between a chain and another chain of polymers.
- Smaller molecules usually combine together to form larger molecules.
- Mixed properties of both the molecules or functional group are taken into consideration..
- A linear polymer is obtained as the condensation product when both functional groups are difunctional.
- When one of the functional groups is tri- or tetra-functional, the polymer formed will be crosslinked polymer having a three-dimensional network.
- 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 crosslink density.
Examples of Condensation Polymerization
Nylon and Polyester are some of the most common examples or products of this type of polymerization.
In the figure given above, there is a reaction between adipic acid monomer and hexamethylene diamine monomer which gives the final product as polyamide and a byproduct which is a water molecule.
HOOC–(CH2)n–COOH + HO–(CH2)m–OH → HOOC–(CH2)n–COO–(CH2)m–OH + H2O
Another form of a condensation polymerization is the reaction between a dibasic acid and a glycol where the polymer formed is known as polyester. The by-product again here is water which is mostly removed.