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Maharashtra State Board Class 12
Chemistry Solutions Chapter 15
Introduction to Polymer Chemistry
- Choose the correct option from the given alternatives. Online learning platforms Question i. Nylon fibers are ………………………………….. A. Semisynthetic fibres B. Polyamide fibres C. Polyester fibres D. Cellulose fibres Answer: B. polyamide fibres Question ii. Which of the following is naturally occurring polymer? A. Telfon B. Polyethylene C. PVC D. Protein Answer: D. Protein Question iii. Silk is a kind of …………………………………. fibre A. Semisynthetic B. Synthetic C. Animal D. Vegetable Answer: C. an animal
Question iv. Dacron is another name of ………………………………….. A. Nylon 6 B. Orlon C. Novolac D. Terylene Answer: D. Terylene Question v. Which of the following is made up of polyamides? A. Dacron B. Rayon C. Nylon D. Jute Answer: C. Nylon Question vi. The number of carbon atoms present in the ring of ε – caprolactam is A. Five B. Two C. Seven D. Six Answer: D. Six Question vii. Terylene is ………………………………….. A. Polyamide fibre B. Polyester fibre C. Vegetable fibre D. Protein fibre Answer: B. Polyester fibre Question viii. PET is formed by …………………………………..
Answer: Question ii. Complete the following statements a. Caprolactam is used to prepare ………………………………….. b. Novolak is a copolymer of …………………………………. and ………………………………….. c. Terylene is ………………………………….. polymer of terephthalic acid and ethylene glycol. d. Benzoyl peroxide used in addtion polymerisation acts as ………………………………….. e. Polyethene consists of polymerised ………………………………….. Answer: a. Nylon- b. Phenol, formaldehyde c. polyester d. initiator (catalyst) e. linear or branched-chain Question iii. Draw the flow chart diagram to show the classification of polymers based on type of polymerisation.
Answer: Question iv. Write examples of Addition polymers and condensation polymers. Answer: Addition polymers : Polyvinyl chloride, polythene Condensation polymers : Bakelite, terylene, Nylon- Question v. Name some chain-growth polymers. Answer: Chain growth polymers : Polythene, polyacrylonitrile and polyvinyl chloride. Question vi. Define the terms :
- Monomer
- Vulcanisation
- Synthetic fibres Answer:
- Monomer is a small and simple molecule and has a capacity to form two chemical bonds with other monomers. Examples : Ethene, Propylene.
- The process by which a network of cross-links is introduced into an elastomer is called vulcanisation or it can also be defined as the
characteristics. Answer: Molecular forces bind the polymer chains either by hydrogen bonds or Vander Waal’s forces. These forces are called intermolecular forces. On the basis of magnitude of intcrmolccular forces, polymers are further classified as ebstomers, fibres, thermoplastic polymers. thermosetting polymers. (1) Elastomers: Weak van der Waals type of intermolecular forces of attraction between the polymer chains are observed in cbstomcrs. When polymer is stretched, the polymer chain stretches and when the strain is relieved the chain returns to its odginal position, Thus, polymer shows elasticity and is called elastomers. Elastomers, the elastic polymers, have weak van der Waals type of intermolecular forces which permit the polymer to be stretched. Lilastorners are soft and stretchy and used in making rubber bands. E.g.. neoprene, vulcanized rubber, buna.S, buna-N. (2) Fibres : It consists of strong intermolecular forces of’ attraction due to hydrogen bonding and strong dipole-dipole forces. These polymers possess high tensile strength. Due to these strong intermolecular forces the fibres are crystalline in nature. They are used in textile industries, strung tyres. etc.. e.g., nylon, terylene. (3) Thermoplastic polymers: These polymer possess moderately strong intermolecular forces of attraction between those of elastomers and fibres. These polymers arc called thermoplastic because they become soft on heating and hard on cooling. They are either linear or branched chain polymers. They can be remoulded and recycled. E.g. polyethenc, PVC, polystyrene. (4) Thermosetting polymers: These polymers are cross linked or branched molecules and are rigid polymers. During their formation they have property of being shaped on heating. but they get hardened while hot. Once hardened these become infusible, cannot be softened by heating and therefore, cannot be remoulded and recycled. This shows extensive cross linking by covalent bonds formed in the
moulds during hardening/setting process while hot. E.g. Bakelite, urea formaldehyde resin. Question ii. Write reactions of formation of : a. Nylon 6 b. Terylene Answer: Terylene is polyester fibre formed by the polymerization of terephthalic acid and ethylene glycol. Terylene is obtained by condensation polymerization of ethylene glycol and terephthalic acid in presence of catalyst zinc acetate and antimony trioxide at high temperature. Properties : Terylene has relatively high melting point (265 °C) It is resistant to chemicals and water. Uses : It is used for making wrinkle free fabrics by blending with cotton (terycot) and wool (terywool), and also as glass reinforcing materials in safety helmets. PET is the most common thermoplastic which is another trade name of the polyester polyethylenetereph- thalate.
Answer: Question vi. Match the following pairs : Name of polymer – Monomer
- Teflon – a. CH 2 = CH 2
- PVC – b. CF 2 = CF 2
- Polyester – c. CH 2 = CHCl
- Polythene – d. C 6 H 5 OH and HCHO
- Bakelite – e. Dicarboxylic acid and polyhydoxyglycol Answer:
- Teflon – CF 2 = CF 2
- PVC – CH 2 = CHCI
- Polyester-Dicarboxylic acid and polyhydoxyglycol
- Polythene – CH 2 = CH 2
- Bakelite – C 6 H 5 OH and HCHO Question vii. Draw the structures of polymers formed from the following monomers
- Adipic acid + Hexamethylenediamine
- e – Aminocaproic acid + Glycine
Answer: Question viii. Name and draw the structure of the repeating unit in natural rubber. Answer: Repeating unit of natural rubber (Basic unit : isoprene) Question ix. Classify the following polymers as natural and synthetic polymers a. Cellulose b. Polystyrene c. Terylene d. Starch e. Protein f. Silicones g. Orlon (Polyacrylonitrile) h. Phenol-formaldehyde resins Answer: Natural Polymers 1. Cellulose 4. Starch 5. Protein Synthetic Polymers
- Polystyrene 3. Terylene 6. Silicones 7. Orion (Polyacrylonitrile) 8. phenol-formaldehyde resin
Question xii. Write name and formula of raw material from which bakelite is made. Answer: The raw material or monomers used to prepare bakelite are o- hydroxymethyl phenol and formaldehyde (HCHO)
- Attempt the following : Question i. Identify condensation polymers and addition polymers from the following. Answer: Question ii. Write the chemical reactions involved in the manufacture of Nylon 6, 6 Answer: Nylon-6, 6 is a linear polyamide polymer formed by the condensation polymerisation reaction. The monomers used in the preparation of Nylon-6, 6 are : (1) Adipic acid : HOOC-(CH 2 ) 4 -COOH (2) Hexamethylene diamine : H 2 N-(CH 2 ) 6 -NH 2
When equimolar aqueous solutions of adipic acid and hexamethylene diamine are mixed and heated, there is neutralization to form a nylon salt. During polymerisation at 553 k nylon salt loses a water molecule to form nylon 6, 6 polymer. Both monomers (hexamethylene diamine and adipic acid) contain six carbon atoms each, hence the polymer is termed as Nylon-6,6. Properties and uses : Nylon 6,6 is high molecular mass (12000 – 50000 u) linear condensation polymer. It possesses high tensile strength. It does not soak in water. It is used for making sheets, bristles for brushes, surgical sutures, textile fabrics, etc. Question iii. Explain the vulcanisation of rubber. Which vulcanizing agents are used for the following synthetic rubber. a. Neoprene b. Buna-N Answer: The process by which a network of cross links is introduced into an elastomer is called vulcanization. Vulcanization enhances the properties of natural rubber like tensile strength, stiffness, elasticity, toughness etc. Sulphur forms cross links between polyisoprene chains which results in improved properties of rubber. For neoprene vulcanizing agent is MgO. For Buna-N vulcanizing agent is sulphur.
Bakelite is used in making articles like telephone instrument, kitchenware, electric insulators frying pans, etc.
- Teflon is polytetrafluoroethylene. The monomer used in preparation of teflon is tetrafluoroethylene, (CF 2 = CF 2 ) which is a gas at room temperature. Tetrafluoroethylene is polymerized by using free radical initiators such as hydrogen peroxide or ammonium persulphate at high pressure. Properties: Telflon is tough, chemically inert and resistant to heat and attack by corrosive reagents. C – F bond is very difficult to break and remains unaffected by corrosive alkali, organic solvents. Uses : Telflon is used in making non-stick cookware, oil seals, gaskets, etc.
Question v. What is meant by LDP and HDP? Mention the basic difference between the same with suitable examples. Answer: LDP is low density polyethylene and HDP is high density polyethylene. LDP is a branched polymer with low density due to chains are loosely held and HDP is a linear polymer with density due to close packing. HDP is much stiffer than LDP and has high tensile strength and hardness. LDP is mainly used in preparation of pipes for agriculture, irrigation and domestic water line connections. HDP is used in manufacture of toys and other household articles like bucket, bottles, etc. Question vi. Write preparation, properties and uses of Teflon. Answer: Teflon is polytetrafluoroethylene. The monomer used in preparation of teflon is tetrafluoroethylene, (CF 2 = CF 2 ) which is a gas at room temperature. Tetrafluoroethylene is polymerized by using free radical initiators such as hydrogen peroxide or ammonium persulphate at high pressure. Properties: Telflon is tough, chemically inert and resistant to heat and attack by corrosive reagents. C – F bond is very difficult to break and remains unaffected by corrosive alkali, organic solvents. Uses : Telflon is used in making non-stick cookware, oil seals, gaskets, etc. Question vii. Classify the following polymers as straight-chain, branched-chain and
Answer:
- Answer the following. Question i. How is polythene manufactured? Give their properties and uses. Answer: LDP means low density polyethylene. LDP is obtained by polymerization of ethylene under high pressure (1000 – 2000 atm) and
temperature (350 – 570 K) in presence of traces of O 2 or peroxide as initiator. The mechanism of this reaction involves free radical addition and H- atom abstraction. The latter results in branching. As a result the chains are loosely held and the polymer has low density. Properties of LDP : LDP films are extremely flexible, but tough chemically inert and moisture resistant. It is poor conductor of electricity with melting point 110 °C. Uses of LDP : LDP is mainly used in preparation of pipes for agriculture, irrigation, domestic water line connections as well as insulation to electric cables. It is also used in submarine cable insulation. It is used in producing extruded films, sheets, mainly for packaging and household uses like in preparation of squeeze bottles, attractive containers, etc. HDP means high density polyethylene. It is a linear polymer with high density due to close packing. HDP is obtained by polymerization of ethene in presence of Zieglar- Natta catalyst which is a combination of triethyl aluminium with titanium tetrachloride at a temperature of 333K to 343K and a pressure of 6-7 atm. Properties of HDP : HDP is crystalline, melting point in the range of 144 – 150 °C. It is much stiffer than LDP and has high tensile strength and hardness. It is more resistant to chemicals than LDP. Uses of HDP :
