Monomers

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.