Polymerization

Several monomers combine chemically to form three-dimensional networks or a chain of elements, and this process is known as Polymerization. These monomers can be the same or different compounds combined to form a polymer. Besides, for a polymer to exhibit unique characteristics, it should be formed as a result of the combination of a minimum of 100 monomers. Usually, one molecule of polymer consists of hundreds and thousands of monomers. 

A stable covalent bond is formed in the case of polymerization, and it helps the newly formed Polymers to have unique traits. This includes high tensile strength, elasticity, capability to form fibers.

Overview and Importance of Polymerization

It is necessary for every student to learn and understand each and every topic in detail, which are included in the syllabus of chemistry. And the same goes for the topic of Polymerisation, the topic is very important in the subject of Chemistry, and hence students need to have a good understanding of the meaning of Polymerisation, the types of Polymerisations, as well as degrees and techniques of polymerization.

But it is just as important for the students to have an explanation that is easy to understand and comprehend, otherwise what happens is a student may find the topic difficult and may give up on it as well. And hence, to avoid such a situation for the students, Vedantu has brought the complete Explanation of the Polymerisation, along with its types, techniques, and Degrees. So that the students can understand the topic easily without any problem.

Vedantu made it possible because the explanation that Vedantu provides for the Polymerisation, along with its types, techniques, and Degrees, is presented in a manner that is easy for eyes and easy for brains. That is to say, the explanation is well formatted so that students can understand each of the sub-topic of the main topic of Polymerisation. And easy for the brain, because the explanation of Polymerisation, along with its types, techniques, and Degrees is written in a simple and lucid language.

Before discussing polymerization, let us first have a quick look at the “Monomer Molecules” and the “Polymer”. So, “mono” means one, and “mer” means part. Monomer molecules are those molecules, which can react with the other molecules and, therefore, manage to form a very large molecule. Now coming to the second word which is a polymer. The word polymer itself means Many (poly) parts (Mer), and hence the macromolecules or a substance or a material that consists of very large molecules, are called polymers.

Now that the meaning of “Monomer Molecules” and the “polymer” is clear, understanding the process of polymerisation becomes a little easier to understand. So, when the monomer Molecules react together in a chemical reaction and form a polymer chain or three-dimensional network, then this process is called Polymerisation.

Types of Polymerisation 

There are many ways in which Polymerisation is formed, a few of which are discussed below.

• Step-growth Polymerisation: When the pairs of reactants of any length, fuse or combine at each step in order to form a longer polymer molecule, then this particular way of forming the polymerization is regarded as the step-growth polymerization. In this process of polymerization, the average molar mass increases gradually but slowly, while the long chains take time to be formed.

• Chain-growth Polymerisation: When the step of chain extension adds to the monomer in a growing chain, with an active center such as cation, or free radical, then such formation of the polymerization, is regarded as a Chain-growth polymerization because here a chain reaction takes place. The unsaturated monomers, especially those which contain the double bonds of carbon-carbon, are all linked together in the chain-growth polymerization. While due to the formation of a new sigma bond the pi bond is lost.

1. Condensation Polymerization 

Condensation polymers are formed by a reaction between two different bifunctional or tri-functional monomer units. These monomeric units undergo a condensation reaction to form polymers and small molecules of simple compounds like HCl (Hydrogen chloride), H₂O (Water), alcohol, etc. are eliminated. Silicon, Bakelite, Nylon, etc. are some of the examples of condensation polymers. 

2. Addition Polymerization 

In case of addition polymerisation, double or triple bond monomers are repeatedly added to form a polymer. In this type of reaction, no by-products are formed. For instance, propene (C₃H₆) helps in the formation of poly-propene ((C₃H₆)_n) and polythene ((C₂H₄)_n) is formed by the addition reaction of ethene (C₂H₄) molecules. 

This can be Further Divided into Two Categories – 

1. Copolymers – Those polymers which are formed due to the addition reaction held between two different kinds of monomers are known as copolymers. Buna-N and Buna-S are examples of homopolymers. 

2. Homopolymers – Those polymers which are formed due to the addition reaction held between the same kinds of monomers are known as Homopolymers. Polythene made from a single kind of monomer ethene is an example of a homopolymer.

Photopolymerisation reactions are also chain-growth polymerization. When the ultraviolet light is absorbed, then it initiates the photopolymerization reaction. The absorbed light can either be direct or indirect, if it is direct then it is due to the reactant monomer, and when it is not direct then it is due to the photosensitizers, which absorbs the light, that is to say, ultraviolet light, and then transfers this energy into the monomer. 

The only difference between the photopolymerization and the ordinary thermal polymerization is that of the initiation because the step of initiation is different in both the polymerization.

Polymerisation Techniques

Each type of polymerisation has a set of techniques using which the chemical reactions take place for the formation of polymers. Here, look at the various polymerization techniques which are used. 

1. Condensation Polymerisation 

• Solution polycondensation 

• Melt polycondensation 

2. Addition Polymerization 

• Solution Polymerization – In this industrial polymerization method, a monomer is to be dissolved in the non-reactive solvent having an initiator or catalyst, which increases the speed of reaction. The polymer formed in the process is also soluble in the same non-reactive solvent.

• Bulk Polymerization – It is also known as mass polymerization and is formed by adding a radical initiator to the pure monomer. However, the monomer must be in a liquid state, and the radical initiator should be soluble. The reaction is exothermic.  

• Emulsion Polymerization – It is a process of radical polymerization which involves a monomer, water that incorporates emulsion, and surfactant. 

• Suspension Polymerization – In this process of heterogeneous radical polymerization, mechanical agitation is used for mixing monomers in their liquid state. 

Degree of Polymerization

The degree of polymerization can be defined as the frequency of repeating units present in a polymer. For instance, if a polymer P is made up of 5 numbers of monomers (M), then its degree of polymerization will be 5. This is the primary feature of polymer that describes its physical properties as well. 

Further, you can calculate its degree using the steps mentioned below. 

1. You need to write down the polymer’s chemical formula first. For instance, take [-(CF₂^-CF₂)_n ^-] Tetrafluoroethylene into consideration. The element enclosed in parenthesis indicates the monomer unit. 

2. Next, you will need to gather the atomic mass of elements that forms a monomer. In this case, Carbon and Fluorine are involved. You need to check the atomic mass of both these elements from the periodic table. The atomic mass of Fluorine and Carbon is 19 and 12, respectively. 

3. Calculate the molecular weight of the monomer using these following steps. 

1. In order to calculate molecular weight, you need to compute the product of atomic mass with the respective number of atoms (Carbon or Fluorine atoms). 

2. Add both the products to get the molecular weight. For Tetrafluoroethylene, it is (19 x 4) + (12 x 2) = 100. 

4. Finally, you need to divide the polymer’s molecular mass with this calculated molecular weight of the monomer. For instance, the degree of polymerization for Tetrafluoroethylene will be 1200 if its molecular mass is 1,20,000. 

Therefore, the degree of the polymerization formula can be defined as the ratio between the molecular mass of the polymer and the molecular weight of the monomer. 

Solve Yourself 

A polymer solution of 1 L comprises a 10 g polymer. Further, various fractions of a non-solvent are added to the solution in a stepwise manner followed by the precipitation of a fraction of polymer samples. The various precipitated fractions of polymers were washed and dried. Then, these are weighed, and then M_n is determined. Then, compute the value of M_w, M_n, and PDI for the polymer that was originally present. You need to assume that the value of M_w and M_n are the same. 

Consider the table mentioned below, which lists the observed data. 

Further, here look at a few popular polymers developed and used in the industry and their properties. 

Multiple-Choice Questions 

1. Choose the option which does not describe a property of the polymer. 

1. Low cost 

2. Low density 

3. High strength 

4. Chemical attack resistance 

2. Choose the right option which describes a polymer formed by combining identical monomers. 

1. Branched polymer 

2. Linear polymer 

3. Homopolymer 

4. Copolymer 

3. The frequency of repeating units of a polymer is called 

1. Monomer 

2. Chain 

3. Molecule 

4. Degree of polymerization

4. Choose the appropriate option which depicts a copolymer. 

1. Linear 

2. Graph 

3. Branched 

4. Network 

5. Choose the appropriate terms which refer to the addition of multiple kinds of monomers for the formation of polymer chains. 

1. Disproportionation

2. Copolymerisation

3. Chain reaction polymerisation 

4. Combination

6.  Choose the appropriate option of polymer additives which improve flexibility. 

1. Reinforcements

2. Lubricants 

3. Stabilizers 

4. Plasticizers 

7. Choose the right molecular structure which can be represented using this figure below. 

1. Cross-linked 

2. Linear 

3. Network 

4. Branche

Now that you are familiar with the concept of polymerization and the degree of polymerization, you will find it convenient to answer the questions in the exam. You can further improve your knowledge of the subject by downloading our Vedantu app and going through the quality notes prepared by our expert tutors. We have a team of professionals on board who work diligently so that you can carve success in your academic career.