What is a Monomer?
Any simple molecule consisting of two or greater than two binding sites with the help of which it forms covalent bonds with other different monomer molecules to form a macromolecule is called a monomer.
Monomers are actually small molecules. These molecules are mostly organic in nature. These molecules can join with other similar molecules and give rise to large molecules. These large molecules are known as polymers. All monomers contain the tendency to form chemical bonds to a minimum of two other monomer molecules. Polymers are nothing but chains having an unknown amount of monomer units.
Synthetic Monomers:
These monomers are artificially made by the combination of different atoms. Then, these synthetic monomers are reacted together to form larger molecules that are used in various industries for several different purposes.
Some important examples of synthetic monomers and their uses:
1) Ethylene gas is considered to be the monomeric unit of polyethylene.
2) Tetra fluoro ethylene (F₂C=CF₂) forms Teflon. It is an ethylene derivative.
Vinyl chloride (H₂C=CHCl), which forms polyvinyl chloride (PVC), and styrene (C₆H₅CH=CH₂), which forms polystyrene, are all examples of derivatives of ethylene.
3) Ethyl methacrylate is an example of an acrylic monomer. When it combines with an acrylic polymer, it catalyzes and then gives rise to an acrylate plastic. This is used to make artificial nail extensions.
4) The monomer precursor for polycarbonate is Bisphenol A (BPA).
5) Epoxide monomers can be cross-linked with themselves to form epoxy, or they can do so with the addition of a co-reactant.
6) Terephthalic acid is considered to be a commoner. Terephthalic acid, along with ethylene glycol, produces polyethylene terephthalate. Esterification reaction occurs here. Organic acid and alcohol react to produce an ester and water.
7) After hydrolysis, dimethyl silicon dichloride produces polydimethylsiloxane.
8) Caprolactam is another important example of synthetic monomers.
Therefore, the building blocks or fundamental structures of polymers are called monomers.
It is important to note that all the simple molecules are not able to act as monomers unless they have two or more binding sites. Only such molecules can be denoted as monomers. So, we cannot consider molecules like water, ethanol, or ammonia to be monomers.
Some common examples of monomers are:
Adipic acid,
Alkenes,
Glycol, and
vinyl chloride
The monomers mentioned below are generally used for synthesizing the acrylic solution polymers.
1) Ethyl methacrylate
2) Styrene
3) Acrylonitrile
4) Ethyl acrylate
Vinyl chloride and vinyl acetate monomers are not included in this monomers group as they are applied in the area of manufacture of polyvinyl acetate polymers and polyvinyl chloride polymers.
Furthermore, acrylic solution polymers can be divided into two different groups:
1) thermosetting acrylics and
2) thermoplastic acrylics.
1) Thermosetting Acrylics:
These are the polymers that contain backbone monomers, making up the bulk of the polymer together. And there is at least one monomer that consists of a reactive group. The latter allows cross-linking to happen with the help of heat or through a catalyst.
Curing is enforced through heat or through suitable radiation. It may be promoted by the application of high pressure or by mixing it up with a catalyst.
Curing enables a chemical reaction that creates extensive cross-linking between polymer chains giving rise to an insoluble and infusible polymer network.
2) Thermoplastic Acrylics:
These are synthesized by the copolymerization of homopolymerization of a mixture of acrylic and methacrylic monomers. These polymers are generally considered to be inert, relatively.
Classification of Monomers:
Monomers have been classified into two different broad classes,
1) natural monomers and
2) synthetic monomers.
About Natural Monomers:
These monomers are essentially the organic molecules that tend to pre-exist in nature and join together to constitute a larger biological molecule. These molecules are hence, responsible for every form of life on our planet.
Natural monomers, also called biological monomers, are subdivided into four different categories.
Monosaccharides
Amino acids
Nucleotides
Isoprenes
Amino Acids
Amino acids are the monomers for protein. The polymerization site is the ribosome. Proteins are not considered to be homopolymers as 20 types of amino acids are used to make proteins.
Exp: Glycine, Cysteine, Glutamine, Arginine, Valine
Nucleotides
Nucleotides are the monomers of poly-nucleic acids, i.e., DNA and RNA. These nucleotides contain a phosphate group, a pentose sugar, and a nitrogenous base. These nucleotide monomers are generally found in the nucleus of the cell.
Monosaccharides
The monomers for carbohydrates are monosaccharides. Glucose is the most abundant natural monomer. It is linked by glycosidic linkages into the polymers starch, glycogen, and cellulose.
Isoprene
Isoprene is a natural monomer.
Isoprene polymerizes to form natural rubber, like cis-1,4-polyisoprene (mostly) and trans-1,4-polymer (rarely). Synthetic rubbers are generally based upon butadiene, and this butadiene is structurally related to isoprene.
FAQs on Monomers
1. What is a monomer in chemistry?
In chemistry, a monomer is a small, simple molecule that can chemically bond with other similar molecules to form a very large molecule, known as a polymer. The key characteristic of a monomer is its ability to form at least two covalent bonds, allowing it to act as a fundamental building block for macromolecules.
2. How are monomers related to polymers?
Monomers are the individual repeating units that link together to form polymers. This process is called polymerization. You can think of it like a chain, where each individual link is a monomer, and the entire chain is the polymer. Without monomers, polymers cannot be created.
3. What are the main types of monomers?
Monomers are broadly classified into two main categories based on their origin:
- Natural Monomers: These are organic molecules that exist in nature and form essential biological macromolecules. Examples include amino acids, nucleotides, and monosaccharides.
- Synthetic Monomers: These are man-made molecules, typically derived from petroleum, that are synthesized in labs and used to create various plastics, fibres, and rubbers.
4. What are some common examples of synthetic monomers and their resulting polymers?
Several synthetic monomers are crucial for industrial applications. Here are some common examples:
- Ethylene (H₂C=CH₂): The monomer for Polyethylene, used in plastic bags and bottles.
- Vinyl Chloride (H₂C=CHCl): The monomer for Polyvinyl Chloride (PVC), used for pipes and window frames.
- Styrene (C₆H₅CH=CH₂): The monomer for Polystyrene, used in packaging and insulation.
- Tetrafluoroethylene (F₂C=CF₂): The monomer for Teflon (Polytetrafluoroethylene), known for its non-stick properties.
5. Why aren't simple molecules like water or ethanol considered monomers?
A molecule must have at least two reactive or binding sites to be classified as a monomer. This allows it to form continuous, long chains with other monomers. Simple molecules like water (H₂O) or ethanol (C₂H₅OH) have only one primary reactive site (the hydroxyl group for condensation) and cannot link together repeatedly to form a polymer chain. Therefore, they lack the necessary functionality for polymerization.
6. What are the four major types of biological monomers and what macromolecules do they form?
The four primary types of monomers in biology are essential for life. They are:
- Amino Acids: The building blocks of Proteins, which perform countless functions in the body.
- Monosaccharides: Simple sugars like glucose are the monomers for complex Carbohydrates such as starch and cellulose.
- Nucleotides: The monomers that combine to form Nucleic Acids like DNA and RNA, which store and transmit genetic information.
- Isoprene Units: These are the natural monomers that polymerize to form Natural Rubber.
7. What is the difference between a monomer, a dimer, and a polymer?
The difference lies in the number of monomer units joined together:
- A Monomer is a single, individual molecule.
- A Dimer is formed when two monomers are chemically joined together.
- A Polymer is a large macromolecule formed when many monomers (from a few hundred to many thousands) are linked together into a long chain or a network structure.
8. How do thermosetting and thermoplastic polymers differ based on their monomers?
The key difference is in the functionality of their monomers. Thermoplastic polymers are formed from monomers that create long, linear chains with no cross-links. This allows the polymer to be melted and reshaped. In contrast, thermosetting polymers use monomers that have reactive groups capable of forming extensive cross-links between chains when heated. This creates a rigid, three-dimensional network that cannot be melted or reshaped once cured.
