Classification of Polymers

A polymer consists of macromolecules (very large molecules), composed of several repeating structural subunits of these molecules. Polymers are today the backbone of four different industries, namely fibers, plastics, elastomers, and varnishes. This term ‘polymer’ is derived from ‘poly’ meaning ‘many’ and ‘mer’ meaning ‘unit’ or ‘part’. Polymers as mentioned above are macromolecules that are formed by repeating structural units on a massive scale. The repeating units are made up of monomers that are simple and reactive molecules. These units have covalent bonds. The formation of polymers from their respective monomers is called polymerization.

It is difficult to classify polymers under one category due to their extremely complex structures, varying behaviors, and broad applications. Thus, we classify polymers based on the following:

1. Source of Availability
2. Structure
3. Polymerization
4. Monomers
5. Molecular Forces

Classification of Polymers based on the Source of Availability

Polymers are classified as natural polymers, synthetic polymers, and semi-synthetic polymers based on the source of availability.

• Natural Polymers

These polymers occur naturally in nature and are found in plants and animals. Additionally, there are also biodegradable polymers called bipolymers. Examples included starch, proteins, rubber, and cellulose.

• Semi-Synthetic Polymers

These polymers are developed from natural polymers and are chemically modified. For example, cellulose acetate, cellulose nitrate, etc.

• Synthetic Polymers

These polymers are completely man-made. Plastic as we use commonly is the most broadly used synthetic polymer. Synthetic polymers are used in industries and several dairy products. Examples include polyether, nylon-6, 6, 6, etc.

Classification of Polymers based on its Structure

Based on structure, polymers are classified as Linear polymers, Branched-Chain polymers, and Cross-Linked polymers.

• Linear Polymers

Linear polymers are structured such that they have long and straight chains. For example, Polyvinylchloride (PVC) is used in electric cables and pipes.  

• Branched-chain Polymers

Branched-chain polymers are those where linear chains form branches. An example is a low-density polythene.

• Cross-linked Polymers

Cross-linked polymers have bifunctional and trifunctional monomers. As compared to linear polymers, these have a stronger covalent bond. Examples include melamine and bakelite.

Classification of Polymers based on Polymerization

Based on polymerization, polymers are classified as addition polymerization and condensation polymerization. 

• Addition Polymerization

In Addition Polymerization, molecules of the same or different monomers add up together on massive scales to form polymers. These monomers are unsaturated compounds like alkenes, alkadienes, and their respective derivatives.

For example, Teflon, Polyvinyl chloride (PVC), poly ethane, etc are addition polymerization.

• Condensation Polymerization

In Condensation Polymerization, there is a repetition of a condensation reaction between two bi-functional or tri-functional monomeric units.

For example, perylene, polyesters, Nylon -6, 6, etc are condensation polymers.

Classification Based on Monomers

Based on the monomers, polymers can be classified as homomers and heteropolymers. 

• Homomer

In homomers, only single types of monomer units are present. An example is Polythene.

• Heteropolymer or co-polymer

Contrary to homomers, heteropolymers are of different types of monomer units. An example is Nylon-6, 6.

Classification Based on Molecular Forces

Based on molecular forces, polymers are classified as elastomers, fibers, thermoplastics, and thermosetting polymers. 

• Elastomers

Elastomers have weak interaction forces. Examples are rubber and Buna-S.  

• Fibers

Fibers have tough, strong, and high tensile strength and very strong forces of interaction. An example is Nylon -6, 6.

• Thermoplastics

Thermoplastics have intermediate forces of attraction. An example is a polyvinyl chloride.

• Thermosetting polymers

Thermosetting polymers improve the mechanical properties of the material greatly. They also provide enhanced heat and chemical resistance. Examples included phenolics, epoxies, and silicones.

Structure of Polymers

Polymers around us are mostly made up of a hydrocarbon backbone. A Hydrocarbon backbone is a long chain of linked carbon and hydrogen atoms, possibly due to the tetravalent nature of carbon.

A few examples of a hydrocarbon backbone polymer are polystyrene, polypropylene, polybutylene. Also, there are polymers that instead of carbon have other elements in their backbone. For example, Nylon has nitrogen atoms in the repeating unit backbone.

Types of Polymers

Based on the type of the backbone chain, polymers can be divided into:

1. Organic Polymers: This consists of the carbon backbone.
2. Inorganic Polymers: This consists of the backbone constituted by elements other than carbon.

Conceptual Questions

Question 1: What is the difference between addition and condensation polymerization?

Answer:

Addition Polymerisation	Condensation Polymerisation
In Addition Polymerization, molecules of the same or different monomers add up together on massive scales to form polymers.	In Condensation Polymerization, there is a repetition of a condensation reaction between two bi-functional or tri-functional monomeric units.
It produces no by-products.	Water, ammonia and HCl as some by-products produced.
It results from the addition of monomers.	It results from the condensation of monomers.
The molecular weight of the polymer is a multiple of the given molecular weight of the monomer.	The molecular weight of the polymer is not a multiple of the given molecular weight of the monomer.
Radical initiators and Lewis acids or bases are catalysts in Addition Polymerisation.	The catalysts in condensation polymerization are acids, bases, cyanide ions, and complex metal ions.
For example, Teflon, Polyvinyl chloride (PVC), poly ethane, etc are addition polymerization.	For example, perylene, polyesters, Nylon -6, 6, etc are condensation polymers.

Question 2: What are the different bases of classification of polymers? 

Answer:

We classify polymers based on the following:

1. Source of Availability
   1. Natural Polymers
   2. Synthetic Polymers
   3. Semi-Synthetic Polymers
2. Structure
   1. Linear Polymers
   2. Branched-chain Polymers
   3. Cross-linked Polymers
3. Polymerization
   1. Addition Polymerisation
   2. Condensation Polymerisation
4. Monomers
   1. Homomer
   2. Heteropolymer
5. Molecular Forces
   1. Elastomers
   2. Fibres
   3. Thermoplastics
   4. Thermosetting polymers

Question 3: What is polymerization?

Answer:

Polymers are macromolecules that are formed by repeating structural units on a massive scale. The repeating units are made up of monomers that are simple and reactive molecules. These units have covalent bonds. Polymerisation is this formation of polymers from their respective monomers.

Question 4: Differentiate between elastomers and fibers.

Answer:

Elastomers	Fibres
Elastomers have elastic properties like rubber-like solids.	Fibres are thread forming solids with tough and high tensile strength.
They have weak interaction forces.	They have strong interaction forces like hydrogen bonding.
Examples are rubber and Buna-S.	Examples are polyesters and Nylon 6, 6.

Question 5: Classify and explain polymers on the basis of monomers.

Answer:

Polymers are macromolecules that are formed by repeating structural units on a massive scale. The repeating units are made up of monomers that are simple and reactive molecules. Based on the monomers, polymers can be classified as homomers and heteropolymers.

Homomer: In homomers, only single types of monomer units are present. An example is Polythene.

Heteropolymer or co-polymer: Contrary to homomers, heteropolymers are of different types of monomer units. An example is Nylon-6, 6.

Question 6: Give examples of natural, synthetic, and semi-synthetic polymers. 

Answer:

Natural Polymers: These polymers occur naturally in nature and are found in plants and animals. Additionally, there are also biodegradable polymers called bipolymers. Examples included starch, proteins, rubber and cellulose.

Semi-Synthetic Polymers: These polymers are developed from natural polymers and are chemically modified. For example, cellulose acetate, cellulose nitrate, etc.

Synthetic Polymers: These polymers are completely man-made. Plastic as we use commonly is the most broadly used synthetic polymer. Synthetic polymers are used in industries and several dairy products. Examples include polyether, nylon-6, 6,6 etc.