Monomers: Definition, Classification and Sample Questions

A simple molecule having two or more binding sites through which it forms Covalent bonds with other monomer molecules to form a macromolecule together is known as a monomer. Monomers are very tiny molecules and are mostly organic by nature. They join together to form various types of polymers. In this article, we will explore the different types of monomers. 

Read More: Saturated and Unsaturated Fats

Key Terms: Molecules, polymer, Polyethylene, hydrolisis, monosaccharides, catalyst, Covalent bonds, macromolecule, glycol, alkenes, adipic acid, monomers

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What are Monomers?

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Monomers are simpler molecules having a tendency to form chemical bonds with atleast two or more monomer molecules. For example glycol, alkenes, adipic acid, etc. act as monomers. It should be noted here that despite being simple molecules, ammonia, ethanol, or water cannot be referred to as monomers. This is because they don’t have two or more binding sites. Hence, a simple molecule can only be referred to as a monomer if it has the ability to form bonds with two or more monomer molecules.

By joining other molecules that are similar in nature, monomers together form a larger molecule known as a polymer. 

Multiple monomers join together to form polymers

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Classification of Monomers

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On the basis of their origin and synthesis, monomers can be further classified as:

1. Synthetic Monomers

• Synthetic monomers are formed artificially by combining various atoms.
• These monomers join together in industries to form large molecules that are used for the benefit of mankind.

For example:

• Polyethylene is composed of the monomer ethylene gas.
• After Hydrolysis of dimethyl silicon dichloride, it produces polydimethylsiloxane.
• The cross-linking of monomers of Epoxide leads to the formation of epoxy. 
• PVC, Polythene, Caprolactam are other such examples.

Polythene Polymer Formation

Monomers like styrene, ethyl methacrylate, acrylonitrile, ethyl acrylate join together to form acrylic solution polymers.

Further, the acrylic solution polymers can be classified into two groups that are:

1. Thermosetting Acrylics: These polymers contain backbone monomers that make up the majority of the polymer together with a minimum of one monomer having a reactive group. This monomer in the presence of heat or a catalyst will allow cross-linkages.
2. Thermoplastic Acrylics: These polymers are formed through the copolymerization or homopolymerization of a mixture of acrylic and methacrylic monomers. These are relatively inert in nature.

2. Natural Monomers

• Natural Monomers are the monomers that exist naturally and are organic in nature. 
• They join together in order to form large biological molecules and the complex structures of biological beings.
• Natural monomers are responsible for sustaining life on Earth.
• These are further divided into four categories:

1. Amino acids
2. Nucleotides
3. Monosaccharides
4. Isoprenes

1. Amino acids

• These molecules contain an acid Carboxyl group (-COOH) and an amino group.
• Amino acids join together to form Protein.
• 20 common amino acids join together for the formation of over 10,000 proteins.

Amino Acid Structure 

2. Nucleotides

• The monomers of nucleotides join together to form poly-nucleic acids such as DNA or RNA (Formally the monomer units of DNA are referred to as deoxynucleotides). 
• Nucleotides are composed of a phosphate group, a nitrogenous base, and pentose sugar.
• These are generally found in the nucleus of a cell.

3. Monosaccharides

• The monomers of monosaccharides join together to form carbohydrates .
• The most abundant naturally occurring monomer is glucose.
• The monomers are linked together with the help of glycosidic linkages into the polymers such as glycogen, cellulose, and starch.

4. Isoprene

• Isoprene monomers combine together to form natural rubber and naturally occurring steroids and terpenes.
• In its purest form, isoprene is a volatile colorless liquid. 
• In human breath, isoprene is a major endogenous hydrocarbon.
• Isoprene mostly forms cis-1,4-polyisoprene. Other Synthetic Rubber are based on butadiene generally which is related structurally to isoprene.

Polymerization of monomer Isoprene leads to the formation of polyisoprene

Read MoreAbout Copolymer

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Things to Remember

• A simple molecule having two or more binding sites through which it forms covalent bonds with other monomer molecules to form a macromolecule together is known as a monomer.
• Synthetic Monomers: These monomers join together in industries to form large molecules that are used for the benefit of mankind.
• Natural Monomers: These monomers join together to form large biological molecules and the complex structures of biological beings.

1. Amino Acids
2. Nucleotides
3. Monosaccharides
4. Isoprene

• Uses of Monomers: Building blocks of important biomolecules such as RNA, used in the synthesis of useful industrial products.

Read More: Polymerisation