Polymers You may think of polymers as being a relatively modern invention however naturally occurring polymers have been used for thousands of years – wood, rubber, cotton, wool, leather, silk,.. etc • Artificial polymers are, indeed, relatively recent and mostly date from after WWII in many cases, the artificial material is both better and cheaper than the natural alternative
A polymer is a large molecule of high molecular mass made by linking together repeating units of small molecules called monomers
Polymerization: process of joining small monomers to form a polymer. • Degree of polymerization(n): the number of monomeric units which combine to form a polymer.
Buna S/ Styrene Butadiene rubber/ SBR/GR-S Rubber • Uses: For making automobile tyres, rubber soles, belts etc. • Buna N/ Nitrile Butadiene rubber/ NBR/ GR-A Rubber Uses: Aeronautical applications, footwear, sponges, floor mats etc.
Classification on basis of Method of Synthesis/Polymerization • Addition or chain growth Polymerization • Condensation or step growth Polymerization • Addition or chain growth Polymerization: done by addition of monomer units having multiple bonds and without the elimination of any molecule. e.g. Polyethene , polypropylene
2) Condensation or step growth polymerizationMonomers containing some active functional groups react together with the elimination of simple molecules like NH3, H2O, CO2 etc.nH2N(CH2)6NH2 + nHOOC(CH2)4COOH (-HN(CH2)6NHCO(CH2)4CO-)n + nH2Ohexamethylene adipic acid nylon-66diamine
Polyamide • Nylon66: • Uses: for making bristles for brushes, blended with wools for making socks and sweaters etc. • Nylon 6 Uses: tyre cords, fabrics and ropes.
. • Nylon 6,10
Polyesters • Terylene/Dacron: • Uses: for making cloths by mixing with cotton, magnetic recording tapes. • Glyptal: Uses: in manufacturing paints and lacquers, building materials such as asbestos, cement etc.
Uses of PET Poly(ethyleneterephthalate) • polyester fabrics are used in apparel and home furnishings such as bed sheets, beds, table sheets, curtains and drape • used in tyre reinforcements, ropes, fabrics for conveyor belts, safety belts, coated fabrics and plastic reinforcements with high energy absorption • Polyester fibers are also used to stuff pillows, comforters and cushion padding
Tacticity: It is relative stereochemistry of adjacent chiral centres within a macromolecule (polymer). • If the monomer unit has a chiral center than different stereochemistry is obtained. Polymerization of such a monomer yield different stereoisomers. • e.g. polymerization of propene. • three types of stereochemistry is possible • Isotactic: If similar groups are all on the same side of the chiral centre i.e. if stereochemistry at all the chiral centre is same within a macromolecules.
Syndiotactic: If stereochemistry at alaternating chiral cnetre is same within a macromolecules. • Atactic: If the stereochemistry at chiral centre is random. within a macromolecules.
Copolymerization • It is process of formation of polymer from different types of monomer units. • E.g. Buna N, Buna S
Thermopalstic on heating becomes Soft on further heating beyond melting point it melt & flow Such properties called plastic deformation. Significance of Plastic deformation: used in molding operation. Thermosetting polymers do not exhibits plastic deformation, because they undergoes cross linking during molding to form 3-D structural material. All monomer units are held together by strong covalent bond throughout the structure. On heating, degradation of polymer occurs instead of plastic deformation due to breaking of covalent bond
Natural Rubber • Synthetic Rubber/Neoprene Uses: For making stoppers, shoe heals, containers for storing petrol, oil and other solvents.
Polystyrene/Styron • Monomer: Styrene Uses: for making hot drink cups, combs, radios and television bodies, tiles to be used in covering ceilings and floors.
Polyacrylonitrile (PAN)/ orlon Uses: for making blankets, sweaters, synthetic carpets etc.
Polytetrafluoroethylene (PTFE)/ Teflon • F2C = CF2 → [ F2C-CF2 ] n • Tetrafluoroethylene Teflon
Properties and uses of polymer • Good fiber-forming material and is converted into commercial fibres. • Have high stretch, high crease and wrinkle resistance. • Highly resistant to mineral and organic acid, but is less resistant to alkalies. • Used for making synthetic fibres like terylene, dacron etc. • For blending with wool to provise better crease and wrinkle resistance. • A glass reinforcing material in safety helmets, aircraft battery boxes, etc.