What are condensation polymers definition reaction mechanism types and real life examples
What is Condensation Polymerization?
Before jumping onto condensation polymers, let us understand what polymers are. Polymers, the word, in itself is self-explanatory. Poly means many, hence polymers are the agglomeration of monomers. Many monomers when combined together form a long chain of monomers.
What is Condensation?
Condensation is the chemical process of loss of small atoms from large monomers which help in the linkage of monomers to form large polymers. The atoms lost in the condensation process recombine with another atom to come out as molecules. Small molecules by-products are mostly water, oxygen, carbon dioxide or hydrogen gas.
To sum up, condensation polymers also known as step-growth polymers are the polymers that are formed when their monomeric units are subjected to condensation.
Condensation Polymers Examples
Condensation is one of the most profound methods of making polymers. Condensation polymerization is applied to make numerous polymers. Polyamides are one of the most important classes of condensation polymers like nylon 6,6. Other Condensation Polymerization examples include nylon 6, Kevlar, polyethylene terephthalate, etc. to name a few.
The pictorial illustration given below represents the generic reaction for the formation of a condensation polymer.
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The illustration below depicts the formation of one of the most important condensation polymer example: Nylon 6,6
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Nylon 6,6 is formed due to the condensation of two polyamides: Hexamethylenediamine and adipic acid. During the process, water molecules are eliminated from the monomeric units and they combine together to form nylon 6,6. So if you're asked to explain condensation polymers, you have your answer!
Condensation Polymerization Mechanism
The formation of condensation polymers takes more time than Addition Polymer formation. It is an endothermic reaction; the net heat exchange in the process is negative. This means that condensation polymer formation absorbs energy, hence the process often requires the provision of extra energy from an external source.
The monomers used in condensation polymers generally have two functional groups, namely amine and carboxylic acid. On the provision of external energy in the form of heat, 2 hydrogen atoms and an oxygen atom are lost, which come out together as a water molecule. Now that atoms are lost, empty valency is created for the formation of new bonds. New bonds are then formed between two monomers. This continues and hence results in a long chain of monomers. The monomer connection happens stepwise, unit by unit. Hence, the condensation Polymerization Mechanism is called step-growth polymerization. Let us understand this with a condensation polymer example:
A monomer of carboxylic acid functional group and amine functional group can join together through an amide linkage.
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During the formation of an amide linkage, a water molecule is lost and a bond is formed between adipic acid and Diaminohexane. An amine group remains at one of the terminal ends of the polymer whereas the other terminal end has a carboxylic acid group. Such a polymer is called a polyamide and in such a case, the byproduct is water. A popular example of polyamide is Nylon 6,6, the formation of nylon 6,6 is depicted pictorially in the reaction given above. The monomers of nylon 6,6 are Hexamethylenediamine and adipic acid.
Condensation Polymerization Examples
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Let us dive deeper into each condensation polymer example and understand them in a better way.
Nylon 6
Nylon 6 is another type of condensation polymer which is formed only by repeated polymerization of caprolactam. Caprolactam is a ring-shaped monomer which consists of amine linkages.
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During polymerization the ring-shaped monomer, caprolactam opens up and forms a long-chained polymer called nylon 6.
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Kevlar
Kevlar resembles a lot in structure with nylon 6,6. Although they are very similar, they have minute differences. The key difference is that the structure of kevlar does not contain amide linkages. Instead, they are joined together by benzene rings. The monomers of kevlar condensation polymer include benzene-1,4-dicarboxylic acid and 1,4-diaminobenzene. Given below are the structures of both the monomers of this condensation polymer example.
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On heating together these monomers condense and lead to the formation of kevlar. Given below is the structure of the kevlar condensation polymer.
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Polyesters
Polyesters are another important class of condensation polymers. Unlike other condensation polymers, polyesters arise from the condensation of carboxylic acid and alcohol. For example, polyethylene-terephthalate.
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Commonly abbreviated as PET or PETE, polyethylene terephthalate is one of the most widely used condensation polymers. We see its usage in numerous places in our daily lives. It's also one of the first condensation polymers to be discovered by scientists and has been in usage for a long time now.
FAQs on Condensation Polymers Formation Mechanism and Applications
1. What is a condensation polymer?
A condensation polymer is a polymer formed by repeated condensation reactions between monomers, with the elimination of small molecules such as H2O, HCl, or NH3. In condensation polymerization, each step joins two monomers and releases a small by-product molecule.
- Occurs between monomers with two or more functional groups (e.g., –COOH, –OH, –NH2).
- Forms polymers such as polyesters, polyamides, and phenol-formaldehyde resins.
- Also called step-growth polymerization.
2. What is the difference between addition and condensation polymerization?
The key difference is that condensation polymerization releases a small molecule as a by-product, while addition polymerization does not.
- Condensation polymerization: Monomers with functional groups react and eliminate small molecules like H2O or HCl.
- Addition polymerization: Unsaturated monomers (e.g., alkenes) join without forming by-products.
- Example: Nylon-6,6 (condensation) vs. polyethylene (addition).
3. What are some examples of condensation polymers?
Common examples of condensation polymers include polyesters, polyamides, and phenol-formaldehyde resins.
- Nylon-6,6 (a polyamide)
- Terylene (PET), a polyester
- Bakelite, a phenol-formaldehyde resin
4. How is nylon-6,6 formed in condensation polymerization?
Nylon-6,6 is formed by condensation between hexane-1,6-diamine and hexanedioic acid with the elimination of water. The simplified reaction is:
n H2N–(CH2)6–NH2 + n HOOC–(CH2)4–COOH → [–NH–(CH2)6–NH–CO–(CH2)4–CO–]n + 2n H2O
- Forms amide linkages (–CONH–).
- Water is eliminated in each linkage formation.
5. What type of monomers are required for condensation polymerization?
Condensation polymerization requires monomers with two or more reactive functional groups.
- Common functional groups: –COOH, –OH, –NH2.
- Monomers must be bifunctional or polyfunctional to form long chains.
- Example: A diacid reacting with a diol forms a polyester.
6. What is a polyester and how is it formed?
A polyester is a condensation polymer formed by reaction between a dicarboxylic acid and a diol, producing ester linkages. The general reaction is:
n HOOC–R–COOH + n HO–R′–OH → [–CO–R–CO–O–R′–O–]n + 2n H2O
- Forms ester linkages (–COO–).
- Water is eliminated as a by-product.
- Example: Polyethylene terephthalate (PET).
7. Why is water formed in condensation polymerization?
Water is formed in condensation polymerization because two functional groups combine and eliminate a small molecule during bond formation.
- Example: –COOH reacts with –OH to form an ester (–COO–) linkage.
- During this reaction, H2O is released.
- This removal of a small molecule is called a condensation reaction.
8. What is the repeating unit in a condensation polymer?
The repeating unit is the structural segment of a condensation polymer that repeats throughout the polymer chain.
- It is derived from the reacting monomers after removal of small molecules.
- For nylon-6,6: [–NH–(CH2)6–NH–CO–(CH2)4–CO–].
- Written inside brackets with subscript n to indicate many repeating units.
9. What is step-growth polymerization?
Step-growth polymerization is another name for condensation polymerization where polymer chains grow by stepwise reactions between functional groups.
- Any two monomers, dimers, or oligomers can react.
- Molecular weight builds up gradually.
- Often involves elimination of small molecules like H2O or HCl.
10. What are the properties and uses of condensation polymers?
Condensation polymers generally have strong intermolecular forces and are widely used in fibers, plastics, and engineering materials.
- Polyamides (nylon): Strong, abrasion-resistant; used in textiles and ropes.
- Polyesters (PET): Durable and lightweight; used in bottles and fabrics.
- Phenol-formaldehyde (Bakelite): Heat-resistant; used in electrical insulators.
