Polymers - Types, Classification, Properties, and Uses of Polymers

Think of a world where many of the conveniences that we have learned to live in our lives today do not exist. No plastic containers to hold food, no synthetic fibers to dress us and keep us warm, and no medical devices to save countless lives. Such a vision puts into focus the importance of polymers. Long chains with repeating structural units called monomers, these sala. Polymers surround us, from the stuffing of grocery items to those in frontline technologies. They occur in both natural, such as proteins and cellulose, and synthetic forms like polyethylene and nylon.

This Story also Contains

1. Understanding Polymers
2. Classification based on source
3. Types of Polymers
4. Classification based on Molecular Forces
5. Classification of polymers on the basis of monomers
6. Classification of polymers on the basis of synthesis
7. On the basis of structure
8. Applications of Polymers
9. Some Solved Examples
10. Summary

Understanding Polymers

Polymers are big molecules consisting of a long chain of repeating units called monomers covalently bonded to each other.

Depending on the nature of the monomers used and the method by which they are synthesized, these molecules may go from very simple linear forms to complicated structures like branches or cross-links. Polymers can be classified in terms of their source, structure, and thermal properties. These unique properties, such as low density, high strength-to-weight ratio, and resistance to corrosion, have made polymers very useful materials for a wide spectrum of applications.

Polymers are the backbone of four major industries, i.e., plastic, fibers, elastomers, and paints. Polymers are large molecules having high molecular masses formed by the chemical combination of a large number of relatively smaller molecules known as monomers. The process by which these polymers are converted into polymers is known as polymerization.
A polymer always consists of hundreds to thousands of repeating structural units. Thus, all polymers are macromolecules but all macromolecules are not polymers.

Classification based on source

On the basis of source, polymers can be classified into three categories:

1. Natural polymers:

These are substances of natural origin, i.e., these are found in nature mainly in plants and animals. The well-known natural polymers are proteins, polysaccharides, and rubber. Other examples include silk, wool, starch, cellulose, etc.

2. Semi-synthetic polymers:

These are the substances that are obtained by using natural polymers, i.e., some modifications are made in natural polymers by artificial means. Nitrocellulose, cellulose acetate, vulcanized rubber, gun cotton, etc. are some of the important examples of this category.

3. Synthetic polymers:

The man-made polymers are called synthetic polymers. Some important synthetic polymers are polyethylene, polystyrene, polyvinyl chloride(PVC), bakelite, nylon, etc.

Types of Polymers

There are two broad classes of polymers: natural polymers and synthetic polymers.

The natural polymers include proteins, nucleic acids, and polysaccharides which become part of living things and take vital roles in biological functions. Meanwhile, synthetic polymers are simply artificial materials developed through chemical reactions. These also include different plastics, rubbers, and synthetic fibers that are devised to have different properties and applications. For example, polyethylene is used in the greatest bulk of any plastic, having a good balance of strength and flexibility; nylon is a synthetic fiber used in clothing and carpets.

Classification based on Molecular Forces

The polymers may also be classified by intermolecular forces, which bind their chains together. It is such forces that determine the physical properties of the polymer and its behavior under different conditions. The following are major types of intermolecular forces in polymers:

1. Van der Waals forces:

Weak attractive forces that cause temporary dipoles due to the uneven circulation of electrons in molecules. Thus, they are responsible for the low melting and boiling points of polymers.

2. Hydrogen bonding:

This is the name given to a hydrogen atom that is covalently bonded to an electronegative atom, usually oxygen or nitrogen, which is in turn weakly bonded to another electronegative atom. Such hydrogen bonding can give some polymers both a high tensile strength and a high thermal stability.

3. Ionic bonding:

This type of bonding joins positively and negatively charged ions, mostly in some specialty polymers used in ion-exchange resins and membranes.

Understanding the classification of polymers by molecular forces explains the variation in their properties and behaviors, an aspect that is of importance during the design and selection of an appropriate polymer for a particular application.

Classification of polymers on the basis of monomers

Based on the nature of repeating structural units, polymers are divided into two categories, viz:

1. Homopolymers:

Polymers whose repeating structural units are derived from only one type of monomer unit are called homopolymers. For example, in the case of polyethylene polymer, which is obtained by polymerization of ethylene molecules, the repeating structural unit, -$\mathrm{CH}_2-\mathrm{CH}_2^{-}$is derived from only one type of monomer, i.e, ethylene.

2. Copolymers:

Polymers whose repeating structural units are derived from two or more types of monomer units are called copolymers. For example, in the case of nylon-6,6, the repeating structural unit,$-\mathrm{NH}-\left(\mathrm{CH}_2\right)_6-\mathrm{NH}-\mathrm{CO}-\left(\mathrm{CH}_2\right)_4-\mathrm{CO}=$, is derived from two monomer units, i.e., hexamethylenediamine and adipic acid.

Classification of polymers on the basis of synthesis

Polymers can also be classified on the basis of the mode of polymerization into two subgroups.

1. Addition polymers:

In this type of polymerization, the molecules of the same or different monomers simply add on one another leading to the formation of a macromolecule in which the molecular formula of the repeating structural unit is the same as that of the starting monomer. The polymers thus formed are called addition polymers. For example, Buna-S, Buna-N, etc.

2. Condensation polymers:

In this type of polymerization, a large number of monomer molecules combine together usually with the loss of simple molecules such as water, alcohol, ammonia, carbon dioxide, and hydrogen chloride to form a macromolecule in which the molecular formula of the repeating structural unit is generally not the same as that of the monomer.

The cationic polymerization is initiated by the use of strong Lewis acids such as $\mathrm{BF}_3, \mathrm{AlCl}_3, \mathrm{SnCl}_4$

On the basis of structure

There are three different types based on the structure of the polymers.

1. Linear polymers
2. Branched-chain polymers
3. Cross-linked or Network polymers

Applications of Polymers

Polymers find applications in many industries, such as

1. Packaging:

Polymers like polyethylene, polypropylene, and polyethylene terephthalate are extensively used in packaging materials for foodstuffs, beverages, and consumer goods.

2. Construction:

Big applications for polymers like polyvinyl chloride and polyurethane are building materials: pipes, insulation, and flooring.

3. Automotive:

Polymers are much used in the car industry for various vehicle parts, like bumpers, dashboards, and tires.

4. Electronics:

Used in making circuit boards, insulating wires, and capacitors as dielectric materials.

5. Medicine:

Polymers have applications in medical devices, prosthetics, and drug delivery systems by reason of their biocompatibility and ease of modification.

The versatility of the polymers has resulted in huge applications, beginning from household items to state-of-the-art technologies. With ever-increasing research development, many new and innovative applications of polymers have continuously been coming into the limelight.

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Some Solved Examples

Example 1
Question: Which of the following is a natural polymer?
1) Poly (butadiene-acrylonitrile)
2) cis-1,4-polyisoprene
3) Poly(Butadiene-styrene)
4) Polybutadiene

Solution:
Cis-1,4-polyisoprene is the polymer found in natural rubber. Therefore, the correct answer is option (2).

Example 2
Question: Identify the example of a natural polymer.
1) Cellulose
2) Rubber
3) Nylon-6,6
4) Enzymes

Solution:
Natural polymers are found in nature and are primarily obtained from plants and animals. Cellulose is a well-known natural polymer. Hence, the correct answer is option (1)

Example 3

Question: The copolymer formed by addition polymerization of styrene and acrylonitrile in the presence of peroxide is:
1) (correct)
2)
3)
4)

Solution:
Styrene is represented as $\mathrm{C}_6 \mathrm{H}_5-\mathrm{CH}=\mathrm{CH}_2$ and acrylonitrile as $\mathrm{CH}_2=\mathrm{CH}-\mathrm{CN}$. The copolymer obtained by the polymerization of styrene and acrylonitrile is a well-known product. Therefore, the correct option is (1).

Example 4
Question: Which of the following is NOT a natural polymer?
1) Protein
2) Starch
3) Rubber
4) Rayon

Solution:
Rayon is a man-made polymer derived from cellulose acetate, making it a synthetic material. Therefore, the correct answer is option (4).

Summary

Polymers are, in one word, part of modern life that covers almost all aspects of our daily lives. Actually, these macromolecules were composed of repeating units called monomers, which could, themselves, be further classified into a number of classes according to their origin, structure, thermal properties, and the kind of intermolecular forces keeping their chains together. Natural polymers, like proteins and polysaccharides, hold a place of pride in biological processes; their synthetic companions, like plastics and rubbers, changed the face of whole industries.