Polymers-compressed.pdf

Welcome to Polymers Introduction Rubber Classification Biodegradable polymers Types of polymerisation Polymers Commercial importance Polymer Greek words Poly Many + Macromolecules mer Unit/part Very large molecules having high molecular mass. 103 107u Polymerisation Polymers are formed by the joinin...

Welcome to Polymers Introduction Rubber Classification Biodegradable polymers Types of polymerisation Polymers Commercial importance Polymer Greek words Poly Many + Macromolecules mer Unit/part Very large molecules having high molecular mass. 103 107u Polymerisation Polymers are formed by the joining of repeating structural units on a large scale. The process of formation of the polymers from the respective monomers that are linked by a covalent bond. Polymerisation Formation of polythene from ethene Example n Ethene monomer Polymerisation n Repeating unit n Polythene polymer Classification of Polymers Source Structure Classification of polymers on the basis of Mode of polymerisation Molecular forces Growth polymerisation Classification Based on Source Natural Polymers Semi-Synthetic Synthetic Natural Polymers Polymers that are derived from plants and animals Example Proteins, cellulose, starch, natural rubber, and more Semi-Synthetic Polymers Polymers that are derived from both petroleum and natural products Rayon, cellulose nitrate, and more Cellulose acetate Cellulose nitrate was used as film negatives. Synthetic Polymers Polymers that are man–made or derived from petroleum oil Examples Plastic Polythene Synthetic fibre Nylon 6,6 Synthetic rubber Buna–S Computer Machinery Nylon 6,6 Buna-S Classification Based on Structure Linear Polymers Branched Cross-linked Linear Polymers Ex: High-density polythene, Polyvinyl chloride (PVC), and more. Polymer consisting of long and straight chains Branched-Chain Polymer Ex: Low density polythene, polypropylene, and more Polymer consisting of linear chains having some branches Cross-linked or Network Polymers Ex: Bakelite, Melamine, and more They are formed from bifunctional and trifunctional monomers. 3o amide They contain strong covalent bonds between various linear chains. Classification Based on Mode of Polymerisation Polymers Addition Condensation Addition Polymers They are formed by repeated addition of monomers possessing double or triple bonds. Ethene Propyne Formation of polythene from ethene No part from the monomer units are lost during polymerisation; they are simply added. Types of Addition Polymers - Homopolymers An addition polymer formed by the polymerisation of only single monomeric species Homopolymer Homopolymers Formation of polythene from ethene n Ethene Polythene Homopolymer n Types of Addition Polymers - Copolymers Addition polymers formed by polymerisation of two different monomers Copolymers Examples: Buna-S, Buna-N, and more Buna - S Catalyst: Na Buna-S 1,3-Butadiene Styrene The two different type of monomers (1,3-Butadiene and Styrene) react and form this copolymer. Buna - S Reaction n +n n Butadiene-styrene copolymer (Buna-S) Buna - N Catalyst: Na Buna-N 1,3-Butadiene Acrylonitrile The two different type of monomers (1,3-Butadiene and Acrylonitrile) react and form this copolymer. Buna - N Reaction n + 1,3-Butadiene Buna-N n Acrylonitrile n Uses of Buna – S and Buna - N Copolymer Uses Buna-S Auto tyres, floor tiles, footwear components, and more Buna-N Oil seals, tank lining, and more Condensation Polymers They are formed by repeated condensation reactions between two different bifunctional or trifunctional monomeric units. Water, HCl, and more Generally, in condensation reactions, the elimination of small molecules takes place. Condensation Polymers The two different type of monomers (Hexamethylene diamine and Adipic acid) react and form this copolymer. Nylon 6,6 Hexamethylene diamine n H2N(CH2)6NH2 + Adipic acid n HOOC(CH2)4COOH NH(CH2)6NHCO(CH2)4CO + n H2O n Condensation Polymers + n Hexamethylene diamine n Adipic Acid _nH O 2 Nylon 6,6 n Classification Based on Molecular Forces Elastomer The mechanical properties of polymer- like tensile strength, elasticity, toughness, etc., are governed by Intermolecular forces like Van der Waals forces and hydrogen bonds Binds the polymer chain Fibres Polymers Thermoplastic Thermosetting Elastomers The polymer chains are held together by the weakest intermolecular forces. Permit stretching This forms a few crosslinks between the chains that help the polymer to retract to its original position after the force is released. Buna-S, Buna-N, Neoprene, and more A synthetic rubber Fibres They are thread-forming solids that possess high tensile strength and modulus. Hydrogen bonding Strong intermolecular forces present. Nylon 6,6, terylene and more Terylene Monomers n Terephthalic acid Ethylene glycol + n n Terylene or Dacron + n H2O Thermoplastic Polymers Linear or slightly branched long-chain molecules Capable of repeatedly being soft on heating and hard on cooling. Polythene, polystyrene, polyvinyl chloride(PVC) and more In thermoplastics, the intermolecular forces of attraction are intermediate between elastomers and fibres. Fibres > Thermoplastics > Elastomers Decreasing order of force of attraction Thermosetting Polymers They are cross-linked or heavily branched polymers. Bakelite, Urea-formaldehyde resins, and more On heating, they undergoes extensive cross-linking in moulds and again become infusible. Cannot be used Thermoplastic Thermosetting It contains long-chain linear polymers and are held together by weak van der Waals forces. It contains a 3D network structure constructed with strong covalent bonds. It usually becomes soft on heating and hard on cooling. It does not become soft on heating. It is expensive. It is less expensive. It is soluble in organic solvents. It is insoluble in organic solvents. It is usually soft, weak, and less brittle in nature. It is usually hard, strong, and more brittle in nature. It can be remoulded. It cannot be remoulded. Growth Polymerisation Depending on the type of polymerisation mechanism, polymers undergo Addition Condensation Chain growth Step growth Chain Growth In this type of polymerisation, the molecules of the same monomer or different monomers add together on a large scale to form a polymer. The monomers used are unsaturated compounds. For example, alkenes, alkadienes and their derivatives. This mode of polymerisation leads to an increase in chain length, and chain growth can take place through the formation of either free radicals or ionic species. However, the free radical governed addition or chain-growth polymerisation is the most common mode. Step Growth The product of each step is again a bifunctional species, and the sequence of condensation goes on. Since each step produces a distinct functionalised species and is independent of each other, this process is also known as step-growth polymerisation. Types of Polymerisation Reactions Polymerisation reactions Addition Chain–growth polymerisation Condensation Copolymerisation Addition Polymerisation The molecules of same monomer or different monomers add together This mode leads to an increase in the chain length. Example Polymerisation of ethene to polythene n Benzoyl peroxide n Mechanism of Addition Polymerisation The mechanism of addition polymerisation involves three steps. Generally, in addition polymerisation, an increase in chain length is governed by free radical mechanism. Step 1 Chain initiation Step 2 Chain propagation Step 3 Chain termination Chain Initiation. 2 Benzoyl peroxide Chain initiator. + Phenyl free radical The process starts with generation of phenyl radical from benzoyl peroxide CO2 Chain Initiation.. + Ethene Here, phenyl radical formed adds to the ethene double bond and thus generating a new and larger radical. Chain Propagation.. + The radical formed adds another molecule of ethene forming new and bigger radical. This repetition of sequence to form bigger radical when reaction goes forward, is chain propagation step. ( ) n. Chain Termination (. )n ( )n +. ( )n ( )n At certain stage, the two radicals combine with each other to form the polymeric product. It is the chain terminating step. Addition Polymers Low density Polythene High density Addition polymers Polytetrafluoroethene Polyacrylonitrile Low Density Polythene (LDP) It is obtained by the polymerisation of ethane under certain conditions (High pressure 1000–2000 atm, Temperature 350–570 K) in the presence of O2 or a peroxide initiator. Reaction n O2, 350–570 K 1000–2000 atm n LDP Reaction occurs by free radical mechanism. Characteristics of LDP 01 02 03 04 Chemically inert Tough Flexible Poor conductor of electricity In bottles In electric wires Uses In toys In pipes In wrappers High Density Polythene (HDP) It is obtained by the addition polymerisation of ethene in a hydrocarbon solvent in the presence of a catalyst (Ziegler–Natta catalyst). Reaction n TiCl4 + (C2H5)3Al 333–343 K, 6–7 atm Low temperature and pressure is required. n HDP Characteristics of HDP 01 02 03 Highly dense Chemically inert Tougher and harder In bottles and pipes In buckets and dustbins Uses In making of plastic plates Teflon It is manufactured by heating tetrafluoroethene with any free radical or persulphate catalyst. At high pressure Reaction n Persulphate High pressure n Teflon Characteristics and Uses of Teflon Chemically inert 01 Resistant to attack by corrosive agents 02 Uses In oil seats and gaskets As surface coating on non-stick utensils Polyacrylonitrile It is obtained by the addition polymerisation of acrylonitrile in the presence of a catalyst. Peroxide Reaction n Peroxide n Polyacrylonitrile (PAN) Condensation Polymerisation Generally, it involves repetitive condensation between two bifunctional groups with loss of simple molecules. H2O, ROH, and HCl The product of each step is again, a bifunctional species. Thus, the sequence goes on. Step growth Polyamides Generally, it is prepared by the condensation polymerisation of diamines with dicarboxylic acids. They possess amide linkages and are an important class of synthetic fibres. Nylons Nylon 6,6 6 carbons 6 carbons Reaction n + n Hexamethylene diamine High pressure Adipic acid 553 K n Nylon 6,6 Nylon 2,6 Reaction 6 carbons 2 carbons +n n Aminocaproic acid Glycine –nH2O Nylon 2,6 n Nylon 6 It is obtained by heating caprolactum with water at a high temperature Reaction 6 carbons n Caprolactam 533–543 K H2 O n Nylon 6 Polyester Polycondensation products of dicarboxylic acids and diols. Examples: Dacron or Terylene It is manufactured by heating a mixture of ethylene glycol and terephthalic acid at 420 to 460 K in the presence of zinc acetate-antimony trioxide catalyst. Dacron/Terylene n + n Ethylene glycol (Ac)2Zn 420–460 K SbO3 Terylene Crease resistant Terephthalic acid n Water repellent In footwear Uses In woollen fibres In safety helmets Phenol-Formaldehyde Polymer It is obtained by the condensation reaction of phenol with formaldehyde. In the presence of an acid or a base catalyst Phenol-Formaldehyde Polymer Preparation Step 1 + CH2O Formation of novolac − H+ or OH + + o-Hydroxymethyl phenol derivatives Phenol-Formaldehyde Polymer n −OH Novolac Used in paints Phenol-Formaldehyde Polymer Step 2 Novolac, on heating with HCHO, undergoes crosslinking to form Bakelite. HCHO Phenol-Formaldehyde Polymer Infusible solid mass Bakelite Melamine-Formaldehyde Polymer It is formed by the condensation polymerisation of melamine and formaldehyde. + HCHO Formaldehyde Melamine Resin intermediate Polymerisation Melamine-Formaldehyde Polymer : n Melamine–formaldehyde polymer Used in Making of Unbreakable Crockery Types of Polymerisation Reactions Addition Polymerisation reactions Condensation Copolymerisation Made by chain growth as well as step growth Copolymerisation Polymerization reaction in which more than one monomeric species are allowed to polymerize. Example Buna-S Rubber Rubber Natural rubber It is manufactured from rubber latex. Colloidal dispersion of rubber in water Synthetic rubber Natural Rubber It is a linear polymer of isoprene. 2-Methyl-1,3-butadiene Also known as cis-1,4-polyisoprene Cis-polyisoprene consists of chains held together by weak van der Waals interaction. And due to its coiled structure, it can be stretched like spring. Elastic properties Natural Rubber n Isoprene Cis-polyisoprene Polymerisation n Natural rubber Gutta–Percha n Cis-isoprene Transpolyisoprene Polymerisation n Gutta–percha Gutta–Percha Gutta–percha is trans–isomer of polyisoprene. It is used to fill a teeth to prevent reinfection. Natural rubber becomes soft at high temperature and brittle at low temperature. > 335 K < 283 K Properties of Rubber 1 Soluble in non-polar solvents 2 Non-resistant to attack by oxidising agents 3 Shows high water absorption capacity Vulcanisation It involves heating a mixture of raw rubber with sulphur in a temperature range. 373–415 K And sulphur forms cross-links at the reactive sites of double bonds. Rubber stiffens Structure of Vulcanised Rubber Points to Remember In the manufacture of rubber tyres 5% of sulphur is used as crosslinking agent. Rubber It is any vulcanisable rubber-like polymer that is capable of getting stretched to twice its length. However, it returns to its original shape and size once the external force is released. Examples: Buna-N, Neoprene Neoprene It is formed from polymerisation of chloroprene. Polymerisation n Chloroprene Neoprene Resistant to vegetable and mineral oils n In hoses In gaskets Uses In diving suits clothing Biodegradable Polymer Polymers that undergo environmental degradation and do not accumulates as solid waste Nylon 2,6 These polymers contain functional groups that are similar to functional groups present in biopolymers. PHBV Proteins, carbohydrates, and more PHBV 3-Hydroxybutanoic acid Poly-β-hydroxybutyrate-Co-β-hydroxyvalerate (PHBV) 3-Hydroxypentanoic acid PHBV It is obtained by copolymerisation of 3-hydroxybutanoic acid and 3-hydroxypentanoic acid. PHBV Reaction n ꞵ 𝛂 + n ꞵ 𝛂 3-Hydroxypentanoic acid 3-Hydroxybutanoic acid n PHBV + n H2O Undergoes bacterial degradation PHBV n + n −nH2O n Uses of PHBV 1 Packaging 2 Orthopaedic devices 3 Controlled release of drug Polymers Used in Daily Life Polypropene Polystyrene Polymers Polyvinyl chloride Urea-formaldehyde resin Glyptal Polypropene Polypropene Monomer Structure Uses Propene n Ropes, toys, pipes, and more Polystyrene Polystyrene Monomer Structure Uses Styrene n Wrapping materials, toys, radios, and more Polyvinyl Chloride (PVC) Polyvinyl chloride Monomer Vinyl chloride Structure Uses n Raincoats, handbags, water pipes, and more Urea-Formaldehyde Resin Urea-formaldehyde resin Monomer (i) Urea (ii) Formaldehyde Structure Uses n Unbreakable cups and laminated sheets Glyptal Glyptal Monomer Structure Uses Paints and lacquers (i) Ethylene glycol (ii) Phthalic acid ( ) n