Polymerization

Introducing 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 combining to form a polymer. Besides, for a polymer to exhibit unique characteristic, 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 case of polymerization, and it helps the newly formed Polymers to have unique traits. This includes high tensile strength, elasticity, capability to form fibres. 

Types of Polymerisation 

The process for the formation of polymers can be classified into two parts – 

  1. Condensation Polymerization 

Condensation polymers are formed by a reaction between two different bifunctional or tri-functional monomer units. These monomeric units undergo 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. 

  1. 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) molecule. 

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 homopolymer. 

  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 homopolymer.


Polymerisation Techniques

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

  1. Condensation Polymerisation 

  • Solution polycondensation 

  • Melt polycondensation 

  1. Addition Polymerization 

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

  • Bulk Polymerization – It is also known as the mass polymerisation 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 polymerisation, mechanical agitation is used for mixing monomers in their liquid state. 


Degree of Polymerization

The degree of polymerisation 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 polymerisation 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. 

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

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


Solve Yourself 

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

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

Fraction Number

Mw = Mn (g /mol)

Weight in Grams (g)

1

2,000

1

2

20,000

5

3

50,000

20

4

1,00,000

5

5

5,00,000

1


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

SI. No. 

Polymer Name 

Properties 

Use 

1

PolyChloroEthene or PVC 

  • It can be prepared as flexible or hard. 

  • It works as an electrical insulator. 

PVC is widely utilised in the manufacturing of pipes, gutters, windows, insulation of electric wires, etc. 

2

Polyethene or Polythene 

  • It is flexible. 

  • One can prepare thin films with polythene. 

  • It is cheap. 

It is used in the manufacturing of food wrap, carrier bags, shampoo bottles, etc. 

3

PolyTetraFluoroEthene or PFTE 

  • It is chemically unreactive. 

  • It is slippery. 

It is used in the manufacture of laboratory containers and coating for non-stick pans. 

4

PolyPropene or Polypropylene 

  • This polymer is strong. 

  • It is flexible. 

  • It resists shattering. 

It is used in the manufacturing of ropes, bowls, buckets, carpets, crates, etc. 


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 

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

  1. Branched polymer 

  2. Linear polymer 

  3. Homopolymer 

  4. Copolymer 

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

  1. Monomer 

  2. Chain 

  3. Molecule 

  4. Degree of polymerisation

  1. Choose the appropriate option which depicts a copolymer. 

  1. Linear 

  2. Graph 

  3. Branched 

  4. Network 

  1. 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

  1. Choose the appropriate option of polymer additives which improves flexibility. 

  1. Reinforcements

  2. Lubricants 

  3. Stabilizers 

  4. Plasticizers 

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

(Image to be added soon)

  1. Cross-linked 

  2. Linear 

  3. Network 

  4. Branched

Now that you are familiar with the concept of polymerization and what is 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. 

FAQ (Frequently Asked Questions)

1. How Reversible Is Polymerization As A Process?

There can be certain conditions in which polymerisation can be a reversible process. In this case, a forward polymerisation process is achieved that converts monomers into polymers. Notably, the process of depolymerisation is a complicated one, which converts the polymers back into monomers. 

2. How Can You Say That All Polymers Are Not Plastic?

It is said that all the plastics are a result of polymerisation and but not all polymers are plastic. For instance, a polymer named Cellulose does not act as plastic as it cannot be processed in a similar manner until it is modified.

3. Why Polymerization Chain Reaction Is Considered Dangerous?

Polymerisation is a chain reaction, and the heat generated during the process accelerates the reaction. The pressure and heat build-up may get out of control, causing hazards like explosion or fire, etc. 

4. What Is The Reason That Ethene Goes Under Addition Polymerisation Reaction?

To contribute in an addition reaction, the monomers must have double or triple bonds. Here, a free radical initiates the reaction as it is highly reactive. The double bonds and the carbon bonds present in Ethene molecule is attacked by this free radical to start a chain of reaction in producing polythene.