 Good morning to one and all. With today's session, we are going to learn about the polymers, that is terms and types of polymerizations. Learning outcome. At the end of this session, students will be able to write the various terms related to polymer and the types of the polymerizations. Content. We are going to learn introduction of polymer, various terms used, calculation of degree of polymerization and types of polymerization. Polymer introduction. The term polymer is derived from the Greek word that is poly means many and mer means units. They are composed of large number of small molecules called as monomers. Polymers are made up of thousands of monomers. They are joined together to form large molecule that is called as a macro molecule. Terms that are involved, the first term is polymers definition. Polymers are macromolecules formed by the linking of a larger number of small molecules. These are called as monomers. Example. When ethylene undergoes polymerization, it forms a polyethylene. So, number of ethylene molecules are joined together because of the pi bond which is present in between two carbons. That increases the length of the molecule that is second polymerization. Polymerization is a process of uniting or linking together of two or more smaller and simpler molecules of similar or different types with or without elimination of byproducts resulting in the formation of a new carbon-carbon linkages. Third, number average molecular weight which is represented by m bar m. The total mass of all the molecules in a polymer sample divided by the total number of molecules present. Mathematically, it can be represented as m bar n is equal to summation of ni mi divided by summation of ni, where ni is nothing but the number of molecules of mass mi. Fourth term that is glass transition temperatures, which is denoted by Tg. The temperature below which the polymer becomes hard and glassy and above which it is softer and flexible is known as glass transition temperature. At this temperature, the polymer transfers from a hard glassy material to a soft rubbery material. Fifth, melting temperature, which is denoted by Tm. The temperature at which crystalline polymer transfers to molten state is known as a melting temperature. Sixth, degree of polymerization. The number of repeating units in a chain formed in a polymer is known as a degree of polymerization. This is represented mathematically as dp is equal to molecular weight of a polymer divided by molecular weight of a monomer. The size of polymer molecule is represented in terms of a degree of polymerization. As the degree of polymerization increases, the substance becomes greasy, then vaccine and finally solid above this dp value of 1000 and is then true polymer. At this moment pause the video and answer this question. The question is structural units of high polymers are called as a fibers, b thermo units, c monomers and d none of this. Well the answer of the question that is structural units of high polymers are called as the answer is c that is monomers. We will just go for calculation of degree of polymerization. With propene gas is polymerized by chain mechanism to form polymer of a molecular weight of 42,000. Calculate the degree of polymerization. Given molecular weight of a propene gas is 42. How to solve this? We know the formula for this degree of polymerization is dp is equal to molecular weight of polymer divided by molecular weight of a monomer. So given data, molecular weight of polymer is given as a 42,000 and molecular weight of a monomer is 42. By putting this value in the above formula, that is dp is equal to molecular weight of polymer divided by molecular weight of monomer. We can get the answer that is 42,000 divided by 42. The answer is 1000. It means that 1000 number of propene units are present in this particular polymer. Second example 62.5 grams of vinyl chloride on polymerization forms a polyvinyl chloride polymer of a molecular weight 36,000. Calculate the degree of polymerization given molecular weight of vinyl chloride is 62.5. Again the formula we know it is a degree of polymerization is equal to molecular weight of polymer divided by molecular weight of a monomer. Given data, that is molecular weight of polymer is given as 36,000. Molecular weight of monomer is 62.5. If we put the values in the formula, we can get the answer that is 576. That is 36,000 divided by 62.5. The answer is 576. Next types of polymerization. There are basically two types of polymerization processes. One is addition polymerization. The second one is condensation polymerization. First, addition polymerization. A reaction that yields a product which is exact multiple of original monomeric molecule without elimination of a by-product is called as addition or chain polymerization. Example, ethylene on addition polymerization gives a polyethylene plastic. The reaction, here n number of ethylene molecules are reacting together that forms a polyethylene molecule. The reaction side is double bond that is pi bond which is present in between two carbon atoms of the ethylene. This consists of sigma bond and pi bond. Pi bond opens up and it forms another bond with another carbon of ethylene molecule and thus the chain continues that gives us polyethylene molecule. Second example, it is polyvinyl plastic that is pbc. Again, the vinyl chloride do contains this double bond. Unsaturation point is present. Again, the reaction side is itself the pi bond. Here, once again the pi bond break opens and the bond formation between two different vinyl chloride molecules takes place and that continues with formation of polyvinyl chloride. This is polyvinyl chloride molecule. A monomeric molecule containing one or more double bonds makes it bifunctional by intermolecular rearrangement. Characteristics of addition polymers are they are linear or straight chain in structure. These are soft and weak. The rate of reaction is very fast. The byproducts are nil. Second condensation polymerization. Those reactions between functional molecules of monomers leading to the production of a polymer with an elimination of small molecules such as water hydrochloric acid etc. are called as condensation polymerization. For example, when hexamethylene diamine react with adipic acid, it gives us a nylon 6-6. But this reaction also involves formation of a small molecule that is byproduct. This won't happen of case of addition polymerization, but this is observed in case of condensation polymerization itself that is a loss of this water molecule. So, here in this case, hexamethylene diamine and adipic acid, they are reacting with each other and that terminates into formation of nylon 6-6 molecule. Characteristics of condensation polymers. It is an intermolecular combination. Polymerization takes place through the different functional groups and polymers shows free dimensional network structure. Also, polymers are hard and strong in nature. The rate of reaction is slow. The byproducts are always formed. References for this session have used in a textbook of engineering chemistry by Jane and Jane. Thank you.