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.

Classification on basis of availability or occurrence Natural polymers e.g. starch, cellulose, proteins, natural rubber Semi-Synthetic polymers e.g. Vulcanized rubber Synthetic polymers e.g. Polyethene, nylon, Teflon

Classification on the basis of:

Classification on basis of monomer units homopolymers One type of monomer units e.g. polyethene copolymers Two or more than two types of monomers e.g. styrene-butadiene rubber

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 polymerization Monomers 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 + nH2O hexamethylene adipic acid nylon-66 diamine

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

Classification on basis of thermal properties Can’t be reshaped. Thermosetting: Undergo chemical changes and cross linking on heating and become permanently hard, rigid on cooling. e.g. Phenol-formaldehyde, Bakellite, Urea formaldehyde resin Can be reshaped Thermoplastic: Soften on heating and can be converted into any shape. E.g. PE,PTFE, PMMA

Classification on basis of intermolecular forces or end use Elastomers: undergo long elongation when pulled and return to original position when released. Buna-S, natural rubber Fibers: long, thin, thread like polymers. Do not undergo stretching or deformation, linked by H-bonding. E.g jute, silk, Nylon 66 Resins: low mol. Wt. polymers, used as adhesives. Liquid or powders e.g. Phenol-formaldehyde Plastics: can be molded into desired shape by heat or pressure e.g. PE, PVC

Classification on basis of elemental composition Organic polymer: Having carbon atoms in their polymer backbone. PE. PVC, PAN Inorganic polymer: Do not have carbon atoms in their polymer backbone. Boron nitride, silicon polymer.

Classification on basis of configuration/stereochemistry

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

Crystallinity Linear structure Polar groups Stereo regularity Avoid bulky group

Elasticity Induce cross linkage Non-polar groups Avoid bulky group

Significance of Plastic deformation: used in molding operation. 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

Chemical structure of basic polymers

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.

LDPE/low density polyethylene: It is formed from ethylene monomer under high temperature and pressure conditions. It is highly branched polymer. Due to branching the polyethylene chains do not packed closely.. Therefore, it has low density. It is used for making thin plastic film bags, insulating wires and cables etc. HDPE/High density polyethylene: It is formed from ethylene monomer in the presence of triethylaluminium ((C2H5)3Al) and Titanium tetrachloride (TiCl4) catalyst (Ziegler Natta Catalyst) at low temperature and pressure. It consists of linear chains. Therefore, the polyethylene chains are closely packed. Hence it has high density. It is used for making containers, pipes etc.

Classification of polymer on basis of electrical properties Insulating polymer Polymer which do not conduct electricity e.g. polyethylene, PVC, PAN etc Conducting polymer Polymer which conduct electricity e.g. polyacetylene, polypphenylene, polyaniline