Polymers

1. 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

3. A polymer is a large molecule of high molecular mass made by linking together repeating units of small molecules called monomers

5. 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.

8. Classification on the basis of:

10. 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.

12. 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

15. 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

16. 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.

17. . • Nylon 6,10

18. 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.

19. 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

23. Classification on basis of intermolecular forces or end use

24. Classification on basis of elemental composition

25. Inorganic polymer [ B=N ]n Boron nitride Silicon Polymer

26. Classification on basis of configuration/stereochemistry/Tacticity

27. 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.

28. Syndiotactic: If stereochemistry at alaternating chiral cnetre is same within a macromolecules. • Atactic: If the stereochemistry at chiral centre is random. within a macromolecules.

30. Conducting polymers • Before 1960 organic polymers used as insulators. • In 1960 Chemist Shirakawa ,Plastic research lab. BASF, Germany, accidentally added a catalyst 1000 times more than the required during polymerization of acetylene ,which result in conducting polyacetylene. • Organic polymers having electrical conductance of the order of conductors are called conducting polymers. • Classification: • Extrinsically conducting polymers (conductivity due to mixing conducting fillers like metal fibers, metaloxide, carbon black with insulating materials) • Also called as Conductive element filled polymers. • Insulation material formed the continuous phase and the added filler form the conducting networks. • Minimum concentration of conducting filler has to be added so that polymers start conducting. • Conductance is not due to matrix is due to fillers.

31. Intrinsically conducting polymers (for example, poly (p- phenylene), polyacetylene, polyaniline) -Conductivity is due to organic polymers themselves. They conduct electricity when doped with Oxidizing ,reducing agents or protonic acids

43. Copolymerization • It is process of formation of polymer from different types of monomer units. • E.g. Buna N, Buna S

45. Strength: Tensile strength increase with molecular mass up to a certain point and then become constant. Commercially a polymer should have high tensile strength.

46. Melt viscosity shows gradual increase with increase in molecular mass.

47. Crystallinity • Crystallinity: Degree of crystallinity of polymer depends on its structure. Linear polymer will have high crystallinity. Eg HDPE is more crystalline than LDPE. LDPE is more crystalline than Polystyrene. Isotactic, syndiotactic highly crystalline. Nylon 66 high degree of crystallinity. Polymers having polar groups can formed hydrogen bond with neigbouring chain.

49. Elasticity: It is mainly because of uncoiling and recoiling of molecular chains on application of force. • Non-elastic Nature of Fibers: The chain mobility is reduced by very close packing of the polymer chain backbone without cross linking. Polar groups and aromatic rings in the backbone chain impart high strength to the polymer fiber.

50. Chemical Resistivity: It depends on the structure of polymer and nature of attacking reagent. When the chemicals attack on polymer, it first softens, swells and loses its strength, and then dissolves. It also depends on several factors such as polar and non polar groups, molar mass, degree of crystallinity, cross linking etc.