POLYMERS Polymers are high molecular weight compounds in the range of 10 4-10 6, whose structures are composed of a large number of simple repeating units. The repeating units are usually referred to as monomers. The conversion process of monomer into polymer is known as polymerization. Example for polymerization: The formation of polyethylene is an example for polymerization. CH 2 =CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 - ETHYLENE POLYETHYLENE (Monomer) (Polymer) The equations for polymerization are represented as below, where n stands for a large number. n CH 2 =CH 2 [-CH 2 -CH 2 -] n Ethylene Polyethylene Polymers are said to be linear, if the repeating units are joined together like links in a chain. The chains may be branched, or joined together by cross-links, or both. More extensive cross-linking may lead to the formation of a three dimensional cross-linked or net-work polymer. TYPES OF POLYMERISATION: There are two main types of polymerization processes namely addition polymerization and condensation polymerization.
Addition polymerization: In addition polymerization process, all the atoms in the monomer are present in the polymer with out the elimination of any molecule. Eg. n CH 2 =CH 2 Ethylene n CH 3 -CH=CH 2 Propylene [-CH 2 -CH 2 -] n Polyethylene [-CH- (CH 3 )-CH 2 -] n Polypropylene Condensation Polymerization: Condensation polymerization proceeds with the elimination of simple molecules like water, ammonia, carbon-dioxide, methanol etc. Eg., A well known example for the condensation polymerization reaction is the formation of Nylon-6,6. It is obtained by heating adipic acid with hexamethylene under Nitrogen at 180-220 0 C.Nylon-6,6 derives its name from its starting materials, adipic acid and hexamethylene, both of which have six carbons. HOOC(CH 2 ) 4 COOH + HNH(CH 2 ) 6 NH 2 - H2O HOOC(CH 2 )CONH(CH2) 6 NH 2 [-CO(CH 2 ) 4 CONH(CH 2 ) 6 NH-] n Nylon-6,6
FREE RADICAL MECHANISM OF ADDITION POLYMERISATION: Addition polymerization takes place either by a free-radical or ionic mechanism depending upon the reagents employed. Free radical polymerization is catalyzed organic peroxides or other reagents which decompose to give free radicals. (1) Chain Initiation: Organic peroxides undergo hemolytic fission to give free radicals. R-CO-O-O-CO-R 2R-CO-O* Unstable 2R* + CO 2 (2) Chain Propagation: Free radical produced in the above step adds to an alkene molecule to form a new free radical. R* + CH 2 =CH 2 R-CH 2 -CH 2 * Ethylene This free radical can attack another alkene molecule and so on. (3) Chain Termination: The chain can be interrupted when two free radical chains combine, or by disproportionation. Combination: * 2R(CH 2 CH 2 ) n CH 2 CH 2 R(CH 2 CH 2 ) n CH 2 CH 2 :CH 2 CH 2 (CH 2 CH 2 ) n R Disproportionation: R(CH 2 CH 2 ) n CH 2 CH 2 * + R(CH 2 CH 2 ) n -CH 2 -CH 2 * R(CH 2 CH 2 ) n CH 2 CH 3 + R(CH 2 CH 2 ) n CH=CH 2
PLASTICS Plastics can be defined as non-metallic moldable compounds which are produced from polymerization of simple molecules. Plastics can be classified on the basis of their physical properties and chemical sources from which they are produced. Classification on the basis of the chemical sources: (1) Cellulose Plastics: Eg, Cellulose nitrate and Cellulose acetate. (2) Synthetic Resin Plastics: Eg. Phenol-formaldehyde, phenolfurfural, urea-formaldehyde, vinyl, styrene and acrylic plastics. These plastics made from phenol, HCHO, urea, acetylene, glycerol and phthalic anhydride. Classification on the basis of physical property: (1) Thermoplastic: A thermoplastic polymer is one which softens on heating and becomes rigid again on cooling. (2) Thermosetting polymer: A thermosetting polymer is one which becomes hard on heating. It cannot be softened by heating. DIFFERENCES BETWEEN THERMOPLASTICS & THERMOSETTING PLASTICS: S.No Thermoplastics Thermosetting plastics 1 2 3 They are readily softened by heat. They are linear in nature. They are addition polymers. They do no soften on heating, on further heating they burn. They have three dimensional network structure, joined by strong covalent bond. They are condensation polymers.
4 5 6 They can be remolded and reused. They are soft, weak and less brittle in nature. They reclaimed from wastes and soluble in organic solvents. They cannot be remolded and reused. They are hard, strong and more brittle. They cannot be reclaimed from wastes and insoluble in all the organic solvents. Preparation of Nylon 6,6: Nylon-6,6 is obtained by heating adipic acid with hexamethylene under Nitrogen at 180-220 0 C.Nylon-6,6 derives its name from its starting materials, adipic acid and hexamethylene, both of which have six carbons. HOOC(CH 2 ) 4 COOH + HNH(CH 2 ) 6 NH 2 - H2O HOOC(CH 2 )CONH(CH2) 6 NH 2 Properties: (i) (ii) [-CO(CH 2 ) 4 CONH(CH 2 ) 6 NH-] n Nylon-6,6 They have high stability because of its melting point(160 0-264 0 C) towards heat and good abrasionresistance. They are insoluble in common organic solvents except in phenol and formic acid. (iii) They are very flexible and retain original shape after use.
Applications: (i) Nylon 6,6 is used for the manufacture of socks, dresses, undergarments, carpets etc due its flexible nature. (ii) It is mainly used for gears, bearings, electrical mountings etc. (iii) They are also used for making filaments of ropes, bristles for tooth-brushes and films, tyre-cords, etc. Preparation of Polyvinyl chloride (PVC): PVC is prepared by heating a water-emulsion of vinyl chloride in presence of a small amount of benzyl peroxide or H 2 O 2 in an autoclave under pressure. n (CH 2 =CHCl) vinyl chloride Polymerization (-CH2-CHCl-) n Polyvinyl chloride Properties: (i) It is a colorless, odorless, and chemically inert powder. (ii) It is resistant to light, atmospheric oxygen, inorganic acids and alkalis but soluble in hot chlorinated ethyl chloride. Applications: (i) PVC is used for the tank-linings, light-fittings, safety helmets, refrigerator components, tyres. (ii) Plasticized PVC is used for making of rain-coats, table cloths, toys, tool-handles, plastic coated cloth, chemical containers, etc. Preparation of Teflon: Ploytetrafluoroethylene (PTFE): Teflon is obtained by the polymerization of tetrafluoroethylene, under pressure in presence of benzoyl peroxide as a catalyst. Polymerization n (CF 2 =CF 2 ) (-CF 2 -CF 2 -) n Properties: (i) Teflon has extreme toughness, high softening point and it shows high resistance towards all chemicals.
Applications: (i) It is used as insulating material for motors, transformers, cables, wires, fittings. (ii) It is used for the manufacture of gaskets, chemical carrying pipes, tanks, etc. Preparation of Polycarbonate: Polycarbonates are prepared by interaction of diphenyl carbonate with bisphenol-a [2,2-bis(4-hydroxyphenyl)propane]. n [ -O- ] 2 C=O + n HO- -C (CH 3 ) 2 - -OH Diphenyl carbonate Bisphenol-A [-O-CO-O- -C(CH 3 ) 2 - --] +2n -OH Polycarbonate Polystyrene and Polyethyleneterephthalate (PET) or Terylene (Dacron): Preparation: PET is one of the commercially important thermoplastic polymer which is obtained by the condensation of ethylene glycol with terphthalic acid in the presence of Antimony Oxide(Sb 2 O 3 ) at elevated temperature. n OH-(CH 2 ) 2 -OH + HOOC - -COOH Ethylene glycol (Sb 2 O 3 ) Terephthalic acid
[ - OH (CH 2 ) 2 -O-CO- CO- ] n PET Properties: (i) PET is a colorless transparent mass. (ii) It has a good fibre forming property with high tensile strength for wrinkle free crease resistant garments. Applications: (i) PET is used for the manufacture of garments with wool and cottons. (ii) It is also used for the manufacture of bottles and containers. Polyurethanes: Preparation: Polyurethanes are prepared by reaction of diisocynates and diols in the presence of Stannic chloride or Stannous octoate at 50-100 0 C. n HO-(CH 2 ) 4 -OH + n OCN - - CH2 NCO [ - CONH CH 2 - NHCOO(CH 2 ) 4 O-] n Polyurethanes Applications: (i) Polyurethanes are used in construction and interior decoration of buildings.
RUBBER Rubbers are high polymers which have elastic properties in excess of 300 %. Natural rubber consists of basic material index which is a dispersion of isoprene. These isoprene molecules polymerize to form long-coiled chains of cis-polyisoprene. n [ CH 2 =C(CH 3 ) CH=CH 2 ] ------ [ -CH 2 -C(CH 3 ) = CH-CH 2 - ] n isoprene Cis-polyisoprene (Natural rubber) -CH 2 -C(CH 3 )=CH-CH 2 - CH 2 -C(CH 3 )=CH- CH 2 - CH 2 -C(CH 3 )=CH- CH 2!---------------------------!-------------------------------!----------------------------- Isoprene unit isoprene unit isoprene unit The m.wt of raw rubber is about 1,00,000-1,50,000. Natural rubber is obtained from saps of the plants like havea brasillians and guayule found in tropical and semi-tropical countries like Indonesia, Malaysia, Ceylon, India. Vulcanization of Rubber: Raw rubber cannot be used directly due to its low tensile strength. To and which makes the rubber as the hard one and this process is known as vulcanization of rubber. Normally vulcanization is done by heating the rubber with sulphur at 100-140 0 C. The sulphur chemically combines with the rubber at the double bonds and makes a cross linking between the chains. -CH 2 -C(CH 3 )=CH-CH 2 - CH 2 -C(CH 3 )=CH- CH 2 - CH 2 -C(CH 3 )=CH- CH 2 -CH 2 -C(CH 3 )=CH-CH 2 - CH 2 -C(CH 3 )=CH- CH 2 - CH 2 -C(CH 3 )=CH- CH 2
Sulphur 100-140 0 C -CH 2 -C(CH 3 )-CH-CH 2 - CH 2 -C(CH 3 )-CH- CH 2 - CH 2 -C(CH 3 )-CH- CH 2 S S S -CH 2 -C(CH 3 )-CH-CH 2 - CH 2 -C(CH 3 )-CH- CH 2 - CH 2 -C(CH 3 )-CH- CH 2 Vulcanized rubber Synthetic Rubber Synthetic Rubbers which has more tensile strength and hard in nature and some of the synthetic rubbers are namely, BUTYL-1-RUBBER:(GR-I or Polyisobutylene) Preparation: Butyl rubber is prepared by the cop[polymerization of isobutene with the trace amount of isoprene in the presence of Aluminum Chloride. The reason for the addition of isoprene, which makes the resulting product vulcanizable. n CH 2 =C(CH 3 ) 2 + n CH 2 =C(CH 3 )-CH=CH 2 Isobutene isoprene [- CH 2 -C(CH 3 ) 2 -CH 2 -C(CH 3 )=CH-CH 2 -] n Polyisobutylene Properties: (i) It is amorphous but crystallizable solid. (ii) Due to its low unsaturation it can be vulcanized and cannot be hardened. (iii) It is very much soluble in solvents like benzene not in alcohol, HCl, HF, etc.
Applications: (i) It is used for the manufacture of insulators employed in high voltage. (ii) Inner tubes of automobile tyres, (iii) For the making of conveyor belts, lining of tanks, hoses etc. STYRENE RUBBER: (GR-S or Buna-S or SBR) Preparation: It is prepared by the co-polymerization of butadiene(75%) and styrene(25%) in an emulsion system at 50 0 C in the presence of cumene hydroperoxide as a catalyst. nch 2 =CH-CH=CH 2 + CH 2 =CH -CH 2 -CH=CH-CH 2 -CH 2 -CH=CH-CH 2 -CH 2 -CH-CH 2 -CH=CH-CH 2 - Stryene Butadiene Rubber Properties: (i) SBR contains double bonds so vulcanization can be done with sulphur or sulphur monochloride(s 2 Cl 2 ). (ii) It swells in oils and solvents and it gets oxidized in the atmosphere. Applications: SBR is used in the manufacture of the followings, motor tyres, foot wears, gaskets, adhesives, tank-lining etc.
COMPOSITES Definition: A composite may be defined as any multiphase material which consists of two or more physically and/or chemically distinct phases with an interface separating them. Composites are obtained from conventional materials like metals, ceramics and polymers by adding fibers, particles etc. Composites have properties like toughness and strength with low weights and high temperature resistance. Types of Composite Materials: Composite materials can be classified on the basis of type of reinforcement used in the matrix, on the basis of type of matrix, and on the basis of number of layers. On the basis of type of reinforcement used in the matrix : (a) Particle-reinforced composite (b) Fibre-reinforced On the basis of type of matrix: (a) Polymer matrix composites(pmc) (b) Metal matrix composites(mmc) (c) Ceramic matrix composites (CMC) On the basis of number of layers: (a) Uni-layer composites (b) Multilayer composites. Polymer Matrix Composites (PMC): Polymer matrix Composites which contain both thermoplastic and thermosetting resins. (i) PMC are tougher and have high strains to failure. (ii) (ii) They posses improved resistance to both hot and wet conditions. (iii) No gases liberated due to chemical inert nature. Eg. Epoxy resins, polyimide, polysulfone and phenolics.
Fibre-Reinforced Composites(FRP): When fibers are used as dispersed phase for the reinforcement of matrices, the resultant composites are known as FRP. FRP have high specific strength and high specific modulus and its strength depends on the following (a) Nature and properties of fibre and matrix materials (b) Strength of the interfacial bond between the fiber and the matrix phases. (c) Length of the fiber. Model Questions: 1. Define polymer and degree of polymerization. 2. What is nylon 6,6. 3. Write the preparation properties and uses of PVC, Teflon, polycarbonate, polyurethane and PET. 4. Differentiate thermoplastics and thermosetting plastics. 5. Define composites. 6. What is co-polymerization? 7. What are composites? Explain the advantages of composites. 8. Explain Fibre reinforced polymer composite. 9. Write notes on matrix composite. 10. Write the preparation, properties and uses of Butyl rubber to SBR. 11. What is monomer? Give one example. 12. What is condensation polymerization? Give one example. 13. What is nylon 6:6? How is it prepared? 14. What is Co polymerization? Give example 15. Name the mechanism by which addition polymerization by which addition polymerization later black. 16. What is PVC prepared and its uses? 17. Give any two applications of poly carbonate? 18. Define degree of polymerization? 19. Define vulcanization? 20. What are plastics? 21. Name the two types of plastics? 22. What is thermoplastic?
23. What is a thermosetting plastic? 24. What is rubber? 25. What is a preparation, properties and uses of Teflon? 26. Give two example of synthetic rubber? 27. Distinguish between national and synthetic rubber? 28. What are the steps involved in free radial mechanism? 29. What is isoprene? 30. Write the use of PET? 31. Give an example for polycarbonate. 32. Write the uses of butyl rubber. 33. Mention the uses of nylon 6:6. 34. Give the properties of nylon 6:6. 35. Define composites? 36. What is FRP give example? 37. Differentiate thermoplastics and thermosetting plastics. 38. Example free radical mechanism. 39. Give the preparation and uses of (i) Teflon, (ii) PVC, (iii) PET, (iv) Polycarbonate, (v) poly urethane, (vi) nylon 6:6 Reference Books: 1.Bahl and Arun Bahl, Advanced organic chemistry 2.Jain and Jain, Engineering chemistry 3.Shashi Chawla, A Text book of Engineering Chemistry.