Note for Applied Chemistry - CHEM by Dheeru Sharma
- Applied Chemistry - CHEM
- Note
- Dr. A PJ Abdul Kalam Tech University Lucknow - AKTU
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INDRAPRASTHA ENGINEERING COLLEGE, GHAZIABAD ENGINEERING CHEMISTRY:KAS-102/202 Module 5 Question –Answer Q.1 Explain the following: a) Polymer, Monomer and Polymerization b) Functionality c) Degree of polymerization d) Ethylene polymerizes but ethane does not. e) Teflon is highly chemical resistant. Ans.(a)Polymer: Polymers is macromolecules formed by the repeated linking of large number of small repeating units. Monomer: Monomer is a repeating unit which combines with each other to form a polymer. Polymerization: Polymerization is a process in which large number of small molecules combine to form a big molecule with or without elimination of small byproducts likewater. (b) Functionality: The number of binding sites present in a monomer is called its functionality. The number of reactive functional group like –NH2 , -OH ,-COOH per molecule of the compound defines its functionality. For a substance to act as a monomer, it must have at least two bonding or reactive sites. The structure of polymers depends upon functionality. Ex. i) CH2 = CH2 Bifunctional (ii) H2N –( CH2 )6–NH2 Bifunctional (c) Degree of polymerization: The number of repeating units in the chains of which a polymer is made up is called degree of a polymerization (n). (d) Ethylene polymerizes but ethane does not: For a substance to act as a monomer, it must be bi-functional in nature, i.e. it must have at least two bonding sites or reactive sites. 1
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Ethylene polymerizes because its functionality is two i.e. bifunctional . (e) Teflon is highly chemical resistant Teflon has distorted (zigzag) structure in which fluorine atoms get packed tightly around folded carbon chain. Since fluorine is highly electronegative, it leads to very strong attractive forces between the different polymeric chains. Due to tightly packed structure and strong force of attraction, teflon is found to be inert And exceptionally high chemical resistance. Q.2 Write the difference between : (a) Thermoplastic and Thermosetting resin. (b) Addition and condensation Polymers. Ans. Thermoplastic resin 1. Polymers which are softened on heating and hardened on cooling . 2. These are processed by addition polymerization. 3. They are linear polymer chain held together by weak vanderwaal’s forces of attraction. 4. They are generally soluble in some organic solvents. 5. They can be remoulded . 6. They are weak, softened less brittle. 7. Ex: PVC,PE, PMMA, Polystyrene. 8. Structure Thermosetting resin 1.Polymes which once hardened can’t be softened again. 2. These are proceed by condensation polymerization. 3. They are branched or cross-linked polymer. 4. They are generally insoluble in some organic solvents. 5..They can’t be remolded. 6. They are strong, hard and more brittle. 7.Ex:Bakelite Phenolic resin ,Epoxy resin. 8. Structure 2
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Addition polymerization Condensation polymerization 1. Addition polymerization is the reaction 1. In condensation reactions, functional groups between monomers undergo polymerization without elimination of any byproduct. 2. Monomer should be an unsaturated molecule. 3. Usually one type of monomers are involved. 4.It is also known as a chain reaction polymerization . 6. No byproduct is formed. 7. Ex: Polythene, PVC,Teflon etc. of two monomers react together releasing a small molecule to form a polymer. 2. Saturated monomers are participating in condensation reaction. 3. Usually more than one type of monomers are involved . 4. It is also known as a step growth polymerization. 6. Byproducts such as H 2O, NH 3 , HCl etc are formed. 7. Ex: Bakelite, Nylon – 6, 6 etc. Q.3 Explain Isotactic, Syndiotactic andAtactic polymers. Or What do you mean by tacticity. Ans.Tacticity : The difference in orderly or disorderly arrangement (configuration) ofmolecules or groups in a polymer is called tacticity. Based on tacticity, there are three types of polymer. (i) Isotactic polymer :- If functional groups are on the same side of the main chain then the polymer is called Isotactic. e.g. Cispolyisoprene( Natural Rubber) (ii) Syndiotactic polymer :- If the functional groups are arranged in alternate fashion around the main chain then the polymer is called syndiotactic. e.g. Transpolyisoprene (Guttapurcha) (iii) Atacticpolymer :- In this type of polymer functional groups are arranged randomly .e.g. Polypropylene. 3
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Q.4 Describe the structure, preparation, properties and uses of following polymers: Terylene, Nylon-66, Nylon-6, Buna-S , Buna-N, and Neoprene. Ans. 1. Terylene or decron or polyethylene tere phthalate (PET) Properties: Terylene is high crystallinity because of its symmetrical structure and presence of polar groups. It is a good fibrous material and the fiber has high modulus and tensile strength. It is resistant to organic solvent and moisture. Uses: (i) It is used as a blend with cotton and wool in clothing. (ii) It is used for making magnetic recording tapes, bottles for cola drinks, fruit juices etc. 2. Nylon-66: 3. Nylon-6: Properties: Uses: Nylons have high m.p. and possess high temperature stability. They are resistance to chemicals. They have linear structure in which molecular chains are held together by H -bonds. They are crystalline and has good mechanical properties. 4
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