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
1. What are condensation polymers?
Condensation polymers are large molecules (polymers) formed by the repeated condensation reactions between monomer units. A key characteristic of this process is the elimination of small, simple molecules like water (H₂O), ammonia (NH₃), or hydrogen chloride (HCl) as a by-product for each new bond formed between the monomers.
2. How does condensation polymerization differ from addition polymerization?
The primary differences lie in their formation mechanism and the monomers involved:
- Mechanism: Condensation polymerization involves a step-growth process with the elimination of a small by-product molecule. In contrast, addition polymerization is a chain-growth process where monomers add to each other without the loss of any atoms.
- Monomers: Condensation polymerization requires monomers with at least two reactive functional groups (e.g., -OH, -COOH, -NH₂). Addition polymerization typically involves unsaturated monomers containing double or triple bonds.
3. Why is condensation polymerization also known as step-growth polymerization?
It is called step-growth polymerization because the polymer chain builds up gradually in a step-by-step manner. Initially, two monomers react to form a dimer. This dimer can then react with another monomer to form a trimer, or it can react with another dimer to form a tetramer. The growth can occur between any two reactive species (monomers, dimers, oligomers), not just by adding monomers to a growing chain, leading to a stepwise increase in the polymer's molecular weight.
4. What are some common examples of condensation polymers used in daily life?
Many everyday materials are condensation polymers. Notable examples include:
- Polyamides (e.g., Nylon 6,6): Used for making textiles, carpets, ropes, and bristles for brushes.
- Polyesters (e.g., Terylene/Dacron): Used in fabrics for clothing, home furnishings, and for making PET bottles.
- Phenol-formaldehyde resins (e.g., Bakelite): Used for making electrical switches, plugs, and handles for cookware due to its heat resistance and insulating properties.
- Melamine-formaldehyde resin: Used to manufacture unbreakable crockery.
5. How is the condensation polymer Nylon 6,6 formed?
Nylon 6,6 is formed through the condensation polymerization of two different monomers: hexamethylenediamine and adipic acid. Each monomer has six carbon atoms, hence the name '6,6'. During the reaction, the amino group (-NH₂) of hexamethylenediamine reacts with the carboxylic acid group (-COOH) of adipic acid. This reaction forms an amide linkage (-CO-NH-) and eliminates one molecule of water as a by-product for each linkage created.
6. What is the main difference between Nylon 6 and Nylon 6,6?
The fundamental difference lies in their monomers. Nylon 6,6 is a copolymer formed from two different monomers (hexamethylenediamine and adipic acid). In contrast, Nylon 6 is a homopolymer formed from a single type of monomer called caprolactam. Caprolactam undergoes a ring-opening polymerization, which is a type of condensation reaction where water first initiates the process.
7. Is Polyvinyl Chloride (PVC) an example of a condensation polymer?
No, PVC is not a condensation polymer. It is a classic example of an addition polymer. PVC is formed by the chain-growth polymerization of its monomer, vinyl chloride (CH₂=CHCl). During this process, the double bonds in the monomers break and the molecules link together without the elimination of any by-product molecules like water.
8. What is a condensation copolymer? Please provide an example.
A condensation copolymer is a polymer formed from the condensation reaction of two or more different types of monomers. A perfect example is Nylon 6,6, which is synthesised from two distinct monomers: hexamethylenediamine and adipic acid. Another common example is Dacron (or Terylene), a polyester formed from the monomers ethylene glycol and terephthalic acid.
9. What are the essential characteristics of monomers that participate in condensation polymerization?
The most crucial characteristic is that the monomers must be bifunctional or polyfunctional. This means each monomer molecule must possess at least two reactive functional groups. These groups, such as hydroxyl (-OH), carboxylic acid (-COOH), amino (-NH₂), or acid chloride (-COCl), allow the monomer to form bonds at two (or more) sites, enabling the creation of a long polymer chain.
10. Do naturally occurring condensation polymers exist?
Yes, many essential biological macromolecules are natural condensation polymers. For instance:
- Proteins: These are polymers of amino acids linked together by peptide bonds, which are formed via a condensation reaction that eliminates a water molecule.
- Polysaccharides (like Cellulose and Starch): These are polymers of monosaccharides (like glucose) joined by glycosidic bonds, which are also formed through dehydration synthesis (a type of condensation).
- Nucleic Acids (DNA and RNA): These are polymers of nucleotides, where phosphodiester bonds are formed with the elimination of water.
