11 Polymer Chemistry GKKole PDF

Unit 4 Chemistry Polymers Polymers- Definition, Classification, Degree of Polymerisation, Functionality, Synthesis, Tacticity, conducting polymers  Macromolecules Macromolecules are large molecules composed of thousands of covalently bonded atoms. The FOUR Class...

Unit 4 Chemistry Polymers Polymers- Definition, Classification, Degree of Polymerisation, Functionality, Synthesis, Tacticity, conducting polymers  Macromolecules Macromolecules are large molecules composed of thousands of covalently bonded atoms. The FOUR Classes of Large Biomolecules – Carbohydrates, Lipids, Protein, Nucleic Acids. Macromolecules are polymers, built from monomers. A polymer is a long molecule consisting of many similar building blocks. These small building-block molecules are called monomers. Macromolecule Monomer Unit Carbohydrates Sugars Lipids Fatty acids Proteins Amino acids Nucleic Acids Nucleotides  Polymer Greek: poly = many; mer = unit or part Polymers are macromolecules formed by the linking together large number of small molecules. High molecular weight n CH2=CH2 (-CH2-CH2-)n Ethylene polymer (poly ethylene or polythene) n = Degree of polymerization = ‘number of repeating units in a polymer is called degree of polymerization’ A species have only a few monomers are bonded together is called ‘Oligomer’. History of Polymers 1839 1500’s Charles Goodyear discovered Mayan Civilization was discovered by vulcanization by heating natural rubber British Explorers. The Mayan are thought with sulfur. Vulcanized rubber is much to be among the first to use polymers, as more stable than the natural rubber. their children were fond of playing with The most common use of vulcanized balls made from local areas. rubber is automobile tyres. 1917 1907 The oldest recorded synthetic plastic, Chemical structure of cellulose was discovered Bakelite was synthesized by Leo by M. Polanyi by X-ray crystallography Baekeland. The hardness and high heat resistivity made it an excellent choice as an electrical insulator. 1920 Development of modern Polymer theory after Staudinger published his research work 1927 entitled Uber Polymerisation Production of polyvinyl chloride resin begins. It is being used till today to make plumbing lines, pipes and bottles. History of Polymers 1938 1930 Nylon was synthesized by W. Carothers Polystyrene was invented, which is widely which is used in manufacture of ropes used in videocassettes and other packaging. etc. Expanded polystyrene (Styrofoam) is used in manufacture of cups, thermally insulated containers and packaging materials. 1941 Polyethylene is developed. Low density and high density polyethylenes are 1970 produced for manufacture of packaging Mouldable high temperature polymers films, pipes, toys etc. (Ekonol) developed by James Economy. Liquid crystal polymers developed from this material an year later. Used for electric devices and aircraft engines. 1971 1976 Kevelar, a polymer which can withstand a The polymer plastic industry temperature of 300 °C is developed by S. Kwolek. outstripped steel as most widely Used in manufacture of bullet proof and fire proof used material. garments for fire fighting and car racing etc. Some commercially important polymers and their year of introduction Polymer Year Polymer Year Styrene-butadiene rubber (SBR) 1930 Silocones 1943 Polyvinylchloride (PVC) 1936 Polyethylene terepthalate 1944 Polychloroprene (Neoprene) 1936 Epoxy resins 1947 Polymethylmethacrylate (PMMA) 1936 ABS resins 1948 Polyvinylacetate (PVA) 1936 Polyethylene, linear 1955 Polystyrene 1937 polyoxyethylene 1956 Nylon-6,6 1939 Polypropylene 1957 Polytetrafluoroethylene 1941 Polycarbonate 1957 Unsaturated polyesters 1942 Ionomer resins 1964 Polyethylene, branched 1943 Polyimides 1965 Butyl rubber 1943 Thermoplastic elastomers 1970 Nylon-6 1943 Aromatic polyamides 1974 Polystyrene and Polyester In order to undergo a polymerization reaction, the monomer must be at least bifunctional. It can make at least two bonds that propagate in two directions. Ethylene moiety is Condensation bifunctional because the pi-bond can be broken and two new sigma bonds can be formed by both the carbon atoms.  Functionality of Polymer Number of reactive sides or bonding sides or reactive functional groups present in the monomers. Most common functional groups in monomers: -OH (hydroxy), -COOH (carboxylic acid) -NH2 (amine) , -SH (thiol), -NCO (isocyanate) Nylon 6,6 Amide functional group in the polymer  Nomenclature of Polymer Homo polymer: same monomeric unit. Only one type of monomer ….M1-M1-M1-M1-M1-M1-... present Example: Polyethylene Copolymer: different monomeric unit. Two or more types ….M1-M2-M1-M2-M1-M2-... of monomers Example: Styrene butadiene present  Nomenclature of Polymer Linear Homo polymer:..M1-M1-M1-M1-M1-M1-.. Cross linked Homo polymer: Monomers are arranged in linear fashion. ….-M1-M1-M1-M1-M1-... Branched Homo polymer: M1 M1 ….-M1-M1-M1-M1-M1-... M1 M1 M1 M1 M1 M1 M1 M1 M1 M1 M1 M1 M1 M1 M1 Monomers are arranged in many One linear chain of monomers having different directions and they are further branching interconnected. Branches are further interconnected. Structure of linear, branched and cross-linked polymers There is no linkage between Short units are connected to the polymer the polymer chains. chain, but are not interconnected. Polymer chains are interconnected / interlinked Linear co-polymer (regular): Two different monomer units are..M1-M2-M1-M2-M1-M2-.. arranged in alternating (systematic) manner. Linear irregular co-polymer: Two different monomer units are..M1-M2-M2-M1-M2-M2-.. arranged not in regular / systematic manner. Block co-polymer:..(M1-M1-M1)(M2-M2-M2)(M1-M1-M1)(M2-M2-M2).. Oligomers of two different monomers are linked together. So one kind of monomers are present in blocks. Stereo-chemistry of Polymer or Tacticity Orientation of functional groups or substituents present in monomeric units in a polymer molecule in an orderly or disorderly fashion with respect to main chain. Difference in arrangement, affect the physical properties (e.g., strength, hardness, elasticity, glass-transition temperature, crystallinity, etc.) of polymers.  Stereo-chemistry of Polymer or Tacticity The side groups can be arranged either in orderly manner or in random manner. Isotactic: All the side groups are Syndioactic: Side groups are arranged in one side (same configuration) arranged in alternating opposite sides. Isotactic and syndiotactic polymers can be crystallized. Atactic: Side groups are randomly arranged. Lowest degree of crystallinity or amorphous in nature. Classification of Polymers based on Synthetic Routes Different types of Polymerization reactions 1. Addition or Chain Growth polymerization. 2. Condensation or Step polymerization. 3. Co-polymerization. 1. Addition or chain growth polymerization Exact multiples of the original monomeric molecules. (Heat, light Catalyst, pressure) Free-radical mechanism  Types of Polymerization 2. Condensation or step polymerization Reaction occurring between simple polar-group containing monomers with the formation of polymer and elimination of small molecules like water or HCl, etc. + water Differences between Addition (Chain) Polymerisation and Condensation Polymerisation Addition Polymerisation Condensation Polymerisation Multiple of one type of monomer unit Two molecular species react together Polymer molecular mass is integral multiple Polymer molecular mass is not integral of monomer molecular mass multiple of monomer molecular mass No by-product formed By-products formed - generally elimination of water, HCl etc. Homo-chain polymer is obtained Hetero polymer chain is obtained. This follows free radical or ionic (cationic, This follows mechanism of condensation anionic) mechanism. reactions, e.g., esterification. High molecular mass polymer is former at Polymer molecular mass increases steadily once with the reaction time. Longer reaction times have a little effect on To get higher molecular weight polymer, molecular weight, it only gives higher yield. longer reaction time is required. At any stage, the reaction mixture contains At any stage, the reaction mixture contains monomer and higher polymer and small all types of molecular species (monomer, fraction (10-8 part) of growing chain oligomer and polymer).  Types of Polymerization 3. Co-polymerization Joint polymerization of two are more monomer species Styrene butadiene rubber Also known as Buna-S  Classification of Polymerization - Based on source 1. Natural polymers Starch : polymer of α-D-glucose Cellulose: polymer of β-D-glucose Natural rubber: polymer of cis- isoprene Protein: Polypeptides (monomer: amino acids) Classification of Polymerization - Based on source 2. Synthetic polymers (man made polymers) Polyethelene (PE), Polypropelene (PP), Polystyrene (PS), Polyvinyl chloride, Nylon, Terylene, Bakelite, etc.  Classification of Polymerization Based on the biodegradability 1. Bio-degradable polymer (biopolymer) 2. Non-bio degradable polymer e.g. Poly(vinyl acetate) (PVA), Polystyrene (PS)  Classification of Polymer Based on form and use 1. Plastic: Hard and tough utility (heat and pressure) e.g., polyethylene, PVC, etc. 2. Elastomer: Vulcanized rubber for good strength and elongation. 3. Fibre: used for reinforcement and to offer mechanical support 4. Liquid resin: Polymers used as adhesives, sealants etc. e.g., epoxy adhesives, polysulphite sealants.  Synthesis of common Polymers Polyethylene (PE) Free-radical mechanism Properties: Rigid, waxy white, translucent and thermoplastic material. Resistance to moisture High pressure-PE- branched structure-flexible & soft Low density poly-ethylene (LDPE) Low pressure-PE-linear structure-high density & better chemical resistance. High density poly-ethylene (HDPE) HDPE has high resistance to organic solvents,.  Polyethylene (PE) Uses: Used as an injection and extrusion moulding material. Insulator parts, bottle caps, flexible bottles. Low Density Polyethylene (LDPE) vs. High Density Polyethylene (HDPE) HDPE : A polyethylene with a linear structure is called HDPE. HDPE is a very strong polyethylene with excellent tensile strength, stiffness, and impact resistance because of how closely its molecules are packed together. In addition to being UV-resistant, HDPE is also chemically resistant. LDPE is a branching of polyethylene, its molecules are less tightly packed. LDPE is consequently less dense than other linear polyethelenes (HDPE). Compared to HDPE, LDPE is more susceptible to stress cracking, less heat resistant, and extremely permeable to gases like carbon dioxide. Due to its extreme flammability, LDPE's employment in high-temperature applications is severely constrained.  Polyvinyl Chloride (PVC) Free-radical mechanism Properties: Colorless, Odourless Chemically inert powder Resistant to light, atmospheric oxygen, inorganic acid and alkali. Soluble in hot chlorinated hydrocarbon (ethylene chloride) More rigidity and stiffness compare to polyethylene  Poly-Vinyl Chloride (PVC) Uses: making sheets tank-lining safety helmets Refrigerator components tyre of cycle and motor cycle Plasticized PVC is used for making continuous sheets. obtained by adding plasticizers such as dibutylphthalate, dioctylphthalate and etc.  Poly-methyl methacrylate (PMMA) Free-radical mechanism Properties: Hard and fairly rigid material It is like rubber above 65 oC High optical transparency, high resistance to sunlight Low chemical resistance: hot acids and alkali Low scratch resistance  Poly-Methyl methacrylate (PMMA) Uses: For making lenses Aircraft light fixtures, Gun turrets Making TV screen and touch screen Semipermeable membranes (in reverse osmosis) Polytetrafluoroethelene (PTFE) Teflon Free-radical mechanism  Polytetrafluoroethylene (PTFE) Teflon Properties: High regular polymer, (Linear polymer) Crystalline powder Melting point: 330 oC High chemical resistant: strong acid (hot fuming nitric acid), alkalis and organic solvents. Molten alkali metals only react with the Teflon. Uses: PTFE is used as a non-stick coating for pans and other cookware. Insulating material (transformers, cables, wire and fittings) Chemical carrying pipes Non lubricating stop-cocks (for burettes) As leak-proof tape in gals cylinder  Styrene Butadiene / Buna S / SBR / GRS Buna – S is synthesized by the polymerization of 1,3-butadiene and styrene in the ratio 3:1. Note: many different polymers can be synthesized by varying the ratio of two ingredients. Buna-N Buna – N is synthesized by the polymerization of 1,3-butadiene and acrylonitrile Other names: Nitrile rubber, nitrile butadiene rubber, NBR, Buna-N, and acrylonitrile butadiene rubber Both the Buna-S and Buna-N are Copolymers.  Polyester Polyesters are polymers formed from a dicarboxylic acid and a diol A) Condensation Direct Esterification Reaction + water It is often known by its trivial name, polyethylene terephthalate (PET). Depending on the nature of dicarboxylic acid and diols, polyester can be aliphatic, semi-aromatic and aromatic. Example: Aliphatic : Polylactic acid (PLA), Polyethylene adipate (PEA), Polybutylene succinate (PBS). Semi-aromatic : Polyethylene terephthalate (PET), Polytrimethylene terephthalate (PTT), Polyethylene naphthalate (PEN). Aromatic : Vectran (polycondensation of 4-hydroxybenzoic acid and 6- hydroxynaphthalene-2-carboxylic acid).  Polyethylene terephthalate (PET) B) Alternatively it can be synthesized by employing the dimethyl ester - Ester Interchange Reaction or Trans-esterification Reaction Increasing the aromatic parts in polyesters increases their glass transition temperature, melting temperature, thermal stability, chemical stability... It is alternatively known as: Dacron and Terylene Polyester – [polyethylene terephthalate (PET)] Properties Polyester fabrics and fibres are extremely strong. Polyester is very durable: stretching and shrinking, wrinkle resistant, mildew and abrasion resistant. Polyester is hydrophobic in nature and quick drying. It can be used for insulation by manufacturing hollow fibres. Polyester retains its shape and hence is good for making outdoor clothing for harsh climates. It is easily washed and dried. Most polyester fibres can withstand weak mineral acids, but can usually be damaged by bases. Depending on the chemical structure, polyester can be a thermoplastic or thermoset.  Polyester (PET) Uses As fibres: polyester fibres are used very widely in clothing and to make the suits and parachutes for sky divers. As films: polyester thin films are used in food packaging, audio and video tapes, electrical insulation, and X-ray films. Packaging: Polyester are also used for packaging, for example for bottles.  Polyurethane Polyurethane (PU) is a polymer having organic units joined by urethane (also known as carbamate). Urethane is a compound that has an O-R group and an NH-R group bonded to the same carbonyl carbon. Polyurethanes are thermosetting polymers but their thermoplastic variants are also available in the market. Polyurethanes are prepared by the polymerization of a di-isocyanate and ethylene glycol. If the reaction is carried out in the presence of a blowing agent, the product is polyurethane foam. Methylene diphenylisocyanate Monomer can vary. Depending on monomer used, the final polyurethane will be different. Their physical and chemical properties will also be different.  Polyurethane Foam Prof. Otto Bayer in 1952 demonstrating his creation. A kitchen sponge made of polyurethane foam High density PU foam used in mattresses. Polyurethane foam is produced in the presence of a blowing agent. The type of foam produced can be controlled by regulating the amount of blowing agent and also by the addition of various surfactants which change the rheology of the polymerising mixture.  Polyurethane Properties Polyurethane has high load capacity in both tension and compression that may change shape under heavy load, but will return to its original shape once the load is removed with little compression. Polyurethanes possess high fear resistance along with high tensile properties. Polyurethane material will remain stable with minimal swelling in water, oil, and grease. Polyurethanes exhibit good electrical insulating properties. Applications Polyurethane foam is used for furniture stuffing, carpet backings, and insulation. One of the most important uses of polyurethanes is in fabrics with elastic properties, such as spandex. Polyurethane materials are commonly formulated as paints and varnishes for finishing coats to protect or seal the wood. Polyurethane is also used in making solid tires and garments.  Bakelite (Phenol formaldehyde resin) Condensation Polymerisation H+ / OH- Cat. Phenol Cross-linked polymer is called Bakelite The linear polymer chain is called Novolac  Bakelite – Properties and Uses Properties Rigid, hard, scratch-resistant, infusible and insoluble solid water-resistant Resistant to non-oxidising acids Resistant to many organic solvents They react with alkali due to the presence of free phenol groups (acidic) Excellent electrical insulator. Uses Electrical insulator parts – switches, plugs, switch-boards etc Moulded articles – telephone parts, TV, radio parts, cabinets Impregnating fabrics, wood, paper In manufacture of paints and varnishes Hydrogen (proton) exchange resin Bearings, for propeller shafts in paper and rolling industry Decorating and show-pieces  Epoxy Resin 60 °C - HCl Condensation polymer Epoxy resin is a thermosetting plastic. It cannot be reclaimed from waste, and therefore cannot be recycled.  Epoxy Resin Properties: high chemical resistant to water, organic solvents acids, alkali and other chemicals High flexibility 5-minutes Epoxy Heat-resistance Excellent adhesive properties due to polar groups Uses: As surface coatings, adhesives like Araldite (for glass, metals etc.) Glass-fibre reinforced plastics ‘Skid-resistant’ surface on highways Epoxy resin moulds are used in making components of aircrafts, automobiles. As laminating material on electrical equipment Epoxy resin furniture and jewellery  Rubber Natural rubber is a polymer called polyisoprene. Polyisoprene can be made synthetically by polymerization of a small molecule called isoprene, with the help of catalysts. In cold weather they would become brittle and crack. Polyisoprene  Crosslinking in Rubber - Vulcanization Most rubber objects are made of some kind of crosslinked rubber. Without crosslinks, the rubber might deform after being stretched over and over again. Vulcanization Vulcanization (cross-linking) to transform weak natural rubber into useful material mold it into whatever shape one wants before crosslinking after it has been crosslinked, it is very difficult to recycle. Crosslinking in Rubber - Vulcanization + Effect of polymer structure on properties 1. Mechanical property (i) Strength (ii) Plastic deformation 2. Physical properties (i) Crystallinity or physical state 3. Thermal Property All these depend on the nature of polymer structure (i) heat resistance 4. Chemical Property (i) Chemical resistance 5. Electrical Properties  Effect of polymer structure on properties Strength: Depends on magnitude and distribution of forces between the polymer chain molecule In straight and branched chain polymer are held together by weak van der Walls forces Strength increases when chain length or molecular weight increases cross linked structure are interlinked by strong covalent forces which makes stronger and tougher. Slipping power of one molecule over the another polymer leads to deformation of polymer  Effect of polymer structure on properties Strength: The strength of a polymer is determined by the extent and distribution of forces of attraction between the molecules. The main forces of attractions are (i) primary or chemical bonding forces (ii) secondary or intermolecular forces. Presence of polar groups (e.g. –CO2H, -OH, -Cl, -F, -CN etc.) increase intermolecular forces. Example: Nylon, Teflon, polyester Presence of van der Waals forces (secondary interactions) make tougher and stronger Strength: Polystyrene > PVC > Polyethylene  Effect of polymer structure on properties Plastic deformation: Change of shape of a polymer on application of heat and pressure This property of polymer helps in moulding the masses into desired shape. (i) Thermoplastic (ii) Thermosetting plastic  Plastic Organic materials of high molecular weight, which can be moulded in any desired form when subjected to heat, pressure, in presence of catalyst. Main component of plastic in the plastic material is resins. Resins: Binding materials which forms a major part of the plastic and it is undergo addition or condensation reaction. Properties: Light weight Good strength Good thermal and electrical insulation (very low thermal and electrical conductance) Low corrosion resistance High refractive index Good dimensional stability High resistance to abrasion (process of scraping or damaged by scrapping)  Plastic Classification: (i) Thermo-plastics and (ii) Thermosetting plastics Thermo-Plastic Linear polymers which show higher degree of plastic deformation These polymers are formed by addition polymerization. For example - polyethylene, poly-styrene, polypropylene etc. These polymer chains held together by weak intermolecular forces. Applied heat and pressure can easily break this weak forces. Consequently, this polymer become soft, flexible, and finally fluid. On cooling become hard. Hardening is not due to chemical reaction, thermoplastic can be reshaped any number of times. Repeated heating and cooling do not affect the chemical nature of the polymer. They can be reclaimed from waste and can be recycled.  Thermosetting Plastic Cross linked polymers which are being formed from their monomers by condensation polymerization. The polymer chains are held together by strong covalent bond. Molecular slippage completely absent because of covalent cross-linking. Consequently, softening does not occur on heating. Due to high degree of cross-linking, they insoluble in any solvent. They normally decompose before melting, resulting permanent set. Which can not be reshaped or reused. They cannot be reclaimed from waste, and therefore cannot be recycled. Example: Polyester, Bakelite, Epoxy resin, etc.  Effect of polymer structure in physical state Relative arrangement of polymer may result amorphous state and crystalline state. Completely random arrangement of molecules leads to amorphous nature When molecules of polymers are arranged in orderly pattern - Crystalline Long repeating unit or low degree of symmetry causes amorphous. (e.g. polystyrene, PMMA and PVA)  Effect of polymer structure in Chemical resistance Chemical nature of monomeric unit and their molecular arrangement determines chemical resistance. Like material attract, while unlike material repels Causing softening, swelling, loss of strength of material. Polymer having −OH, −COOH group swell or dissolved in polar solvents. (water, chloroform, alcohol, etc.) Polymer having methyl (−CH3), phenyl (−C6H5) group swell or dissolved in non- polar solvents (benzene, toluene, petrol, carbon tetrachloride). They have resistance towards water, ethanol. Polymers with more aliphatic groups - soluble in aliphatic solvents Polymers with more aromatic groups – soluble in aromatic solvents Crystalline polymers exhibit higher degree of chemical resistance as compared to amorphous polymers. Greater the cross-linking in the polymer, lesser will be the effect of external chemicals in terms of solubility and strength.  Effect of polymer structure in Thermal properties Glass transition temperature (Tg): The temperature below which the polymer is hard. Above this temperature, the polymer is soft. Hard brittle state is glassy state. Soft flexible state is rubbery state. Polymers with high molecular weight, stronger intermolecular forces and having crystalline nature have a high glass-transition temperature. Polyethylene Tg = -125 oC (absence of intermolecular force and only Hydrogen) Nylon 6,6 : Tg = 50 oC (presence of strong intermolecular hydrogen bonding due to polar group)  Effect of polymer structure in Elasticity Elongated under stress, and its get back the original state on release of stress. Polymer with elastic character called elastomers. Cross linked covalent bond contribute for this elastic character. Q. Why is Teflon highly chemical resistant? Due to presence of most electronegative element fluorine in Teflon , there is very strong attractive forces between its different chains. It does not easily get affected by external chemicals. Q. Why is plasticizer used during manufacturing of plastics? Added plasticizer improves plasticity and flexibility of the plastic mix which causes reduction of temperature and pressure required during moulding process Q.Why do all simple organic molecules not produce polymers? A monomer is an organic and inorganic molecule which should be at least bifunctional. For example, ethylene is bifunctional i.e. has two bonding sites per molecule. So, it is capable of forming polymer. On the other hand, molecules like C2H6, C2H5Cl, etc, are only monofunctional and therefore cannot form polymer. Q. Can Bakelite be reused or recycled? No. Bakelite is a thermosetting polymer. Is has an extensive cross- linked structure. It cannot be recycled. Q. Why do rubbers stretch ? Rubber molecules are polymers, that is they are shaped like very long chains. When the piece of rubber is just sitting there, the molecules are just tangled up in a random mess. When the molecules are like this we say they have a high degree of entropy. But when the rubber is stretched, the chains become aligned in one direction. As soon as one lets go of the stretched rubber, those chains are going to try to become disordered again.