General Introduction and Classification of Polymers

We are surrounded by polymers everywhere. Polymers are large molecules or macromolecules that are made up of many subunits. There are two main types of polymers: natural polymers, which are found in plants and animals, and synthetic polymers, which are man-made and produced by humans. 

Polymers are widely used due to their unique chemical and physical properties. The polymerisation process involves the creation of polymers through a reaction that transforms monomers into polymer chains. The resulting substance is a polymer. 

In biology, macromolecules are almost exclusively polymeric; that is to say, they are composed of long polymer chains.

Polymers

Our surroundings are filled with many polymers made up of hydrocarbon backbones. A hydrocarbon chain, as the name itself suggests, is made up of long chains of carbon and hydrogen atoms. Polypropylene and polystyrene are examples of hydrocarbon backbones. 

Polymers can be classified according to their backbone chain type in the following:

Organic polymers

An organic polymer has a backbone composed of carbon atoms. These only consist of covalent bonds of carbon-carbon. Only organic monomer molecules can form these polymers. Since these polymers are biodegradable, they are largely environmentally friendly. Organic polymers can be found in both natural and synthetic forms. Proteins are an example of organic polymers.

Inorganic polymers

Inorganic polymers are polymers whose backbones do not contain carbon. Due to the presence of organic regions, they are mainly hybrid polymers. Furthermore, these polymers are not biodegradable, which means they are not environmentally friendly. Examples of inorganic polymers include siloxanes, silicones and sulphur chains.

Uses of Polymers

The modern world would look very different without synthetic polymers. We use them today in almost every area of life. 

• Bakelite is used in products such as electrical switches, toys, jewellery, and many others
• Besides its use in the making of sewage pipes, polyvinyl chloride serves primarily as an insulator in electricity cables
• Polystyrene is used in everyday products like containers, trays, disposable plates, and cups
• Clothes, furniture, and even doors and windows are made from polyvinyl chloride

Properties of Polymers

The chemical properties of polymers are primarily determined by the attraction between polymer chains. A hydrogen bond and an ionic bond are incorporated into the polymer. A dipole-dipole bond between side chains gives the polymer high flexibility.

The physical properties of polymers include gaining tensile strength as their chain length and cross-linking increase. As polymers change from crystalline to semi-crystalline shape, they become less susceptible to melting.

When a polymer is to be stretched, its tensile strength becomes one of its most essential properties. For example, fibres have to have excellent tensile strength.

Classification of Polymers

The complexity of polymer structures, the variety of their behaviours, and the variety of their applications make the classification of polymers impossible. Therefore, polymers can be classified by considering the following factors.

Source of Availability

Polymers can be obtained in three ways: naturally, synthetically, and semi-synthetically.

• Natural polymers

These are polymers that are derived from nature. They are derived from various sources, including plants, animals, and microbes. Examples of natural polymers include cellulose and starch. Natural polymers also include nucleic acids such as DNA and RNA, components that are crucial to the life processes of all living organisms. Nucleic acids and proteins are polymers that are present in our bodies.

• Semi-synthetic polymers

Generally, chemical modifications are made to naturally occur polymers to produce these polymers. Examples include cellulose nitrate and vulcanised rubber. 

• Synthetic polymers

These are man-made polymers derived from petroleum. In terms of utility, they can be further classified into three types: thermoplastics, elastomers, and synthetic fibres. A variety of products around the world, nylon 6 for instance, contain them. 

Monomer Chain Structure

Polymers can also be categorised based on the chain structures of their monomers. These are linear, branched-chain, and cross-synthetic polymers.

• Linear polymers

Polymers consisting of monomers with one end group are linear polymers. Fibres and meshes made from linear polymer are strong, resilient, and hard to penetrate. Teflon is one such example. 

• Branched-chain polymers

When the long polymer chain splits into groups of units, branched polymers appear. They are less dense and tensile than linear polymers, and their melting points are lower. Example: polypropylene. 

• Cross-linked polymers

A trifunctional and bifunctional monomer is present in them. Compared to other linear polymers, they can form a stronger covalent bond. Example: silicones. 

Polymerisation

Creating polymers from monomers is known as polymerisation. Polymers derived from processes of addition and condensation fall under this category.

• Addition polymerisation

In addition to polymerisation, monomers are linked simply without producing other products. Chain polymerisation can create additional polymers. Example: polyethene.

• Condensation polymerisation

Condensation polymerisation creates the polymer by joining the molecules together. As a result, small molecules are lost as byproducts. Hydrogen chloride and water are the byproducts formed. Example: polyamides.

Monomers

A monomer is a simple molecule covalently linked to other monomers through at least two binding sites. Through this, it forms a macromolecule by covalently linking monomers together. Homomers and co-polymers fall under this category. 

• Homomer: Homomer is polymers derived from polymerising compounds of the same kind
• Co-polymers: Polymerisation occurs between two or more compounds resulting in co-polymers
• Co-polymers are commonly used in commercial polymers. For instance: nitrile rubber 

Molecular Forces

Elastomers, fibres, thermoplastics, and thermosetting polymers fall under this category.

• Elastomers

Weak intermolecular forces hold elastomer molecules together. Despite being stretched greatly, they revert to their original shapes and sizes. For instance: rubber.

• Fibres

There is a high tensile strength, a high degree of toughness, and a high degree of forces of interaction. For instance: nylon-6.

• Thermoplastics

Upon heating, thermoplastic polymers become malleable and can be moulded but solidify once cooled. The molecular weight of thermoplastics is typically high. For instance: polyvinyl chloride.

• Thermosetting

Polymers such as these increase the mechanical properties of a material as well as its chemical resistance and heat resistance. For instance: silicones.

Based on Conducting Electricity

As a result of their ability to conduct electricity, polymers fall under the classification of conducting polymers.

• Intrinsically conducting polymers: The conductivity of these polymers is caused by their solid backbones consisting of extensive conjugated systems
• Inorganic conducting polymers: They contain charge transfer complexes in which metal atoms interact with polydentate ligands
• Extrinsically conducting polymers: In an extrinsically conducting polymer, conductivity is due to ingredients that are externally added to the polymer

Conclusion 

In the polymerisation process, the monomers of polymers react together to create polymer chains. A polymer chain is formed by the atoms bonded together like links in a chain. Polymers vary in their properties based on which molecules are bonded and how they are bonded. 

In the course of daily life, polymers serve essential roles due to their wide range of properties. Polymers can be enhanced or tailored to have specific properties by combining them with other materials.