Polymers
- 1. Polymers An Introduction to Polymer Chemistry
- 2. •Polymer(Greek: poly=many; mer=part) giant, complex molecules •Made up by the linking together of large number of small molecules (repeating units called monomers ) held together by covalent bonds (two or more bonding sites) Introduction
- 3. Monomers Alkenes, vinyl chloride, adipic acid, glucose, amino acids, glycol with two bonding sites act as monomers C C H H H H E t h y l e n e ethane-1,2-diol Aminoacid hexane-1,6-diamine adipic acid terephthalic acid Isoprene
- 4. Butadiene, MW 54 Polybutadiene, MW 200000 Polymerization MW 28 MW 28000 Monomer Polymer
- 5. Degree of Polymerization •Number of repeating units in the polymer chain formed is called the degree of polymerization (n). •Polyethene: (C2H4)n, where n stands for DP •Molecular weight of PE, M = nMo, where Mo is molecular weight of monomer •Strength of the polymer can be increased by increasing its DP –High DPhard and heat resistant –Low DP soft, gummy
- 6. •Data:If MW of PE, M = 28000, MW of repeat unit, Mo = 28, M = nMo •Thus, n = M/Mo = 28000/28 = 1000 Degree of Polymerization (n) = 1000 Degree of Polymerization
- 7. Classification i) On the basis of origin –Natural –Synthetic ii) On the basis of nature of monomer •Homopolymers(comprise of monomers of the same type) –Linear (homochain or heterochain) –Branched –Cross-linked •Heteropolymers/ Copolymers (Different repeating units) –Linear; Branched; Graft (regular/irregular); Block (regular/irregular) iii) On the basis of chemical nature •Organic (polymer backbone chain made up of carbon atom) •Inorganic (No carbon atoms in the backbone chain, eg., Silicone rubbers)
- 8. Homopolymer: Monomers of the same type Copolymer: Different repeating units Random copolymer: Two or more different repeating units are distributed randomly Alternating copolymer: Alternating sequences of different monomers Block copolymer: Long sequences of a monomer are followed by long sequences of another monomer Homopolymers can be linear, branched or cross-linked Nomenclature
- 9. Graft copolymer: Chain made from one type of monomer with branches of another type
- 10. Tacticity: Orientation of monomeric units in polymer takes place in orderly/disorderly fashion w.r.t main chain. The difference in configuration affects their physical properties Isotactic: Head-to-tail configuration Functional groups are all on the same side of the main chain, FG= Y Tacticity:
- 11. Syndiotactic: Functional groups occupy alternating position. Atactic: Functional groups arranged in random manner For example, atacticpolypropylene is a gummy solid, while isotactic version is highly crystalline & tough. Tacticity:
- 12. •Polymerization Fundamental process in which low molecular weight compounds combine to form giant molecules/ macromolecules of high molecular weight Three types of polymerization •Addition •Condensation •Copolymerization Types of Polymerization
- 13. Addition Polymerization •formed from the monomer, without the loss of any byproduct, like small molecules. Monomers with double or triple bonds tend to polymerize without the liberation of small molecules. Example: Polyethylene (PE) •It yields product that is an exact multiple of the original monomer unit
- 14. Common Polyolefins Monomer Polymer Ethylene H3C CH3 n Repeat unit Polyethylene CH3 CH3 n CH3 CH3 CH3 CH3 CH3 CH3 CH3 Propylene Polypropylene Ph CH3 n Ph Ph Ph Ph Ph Ph Ph Styrene Polystyrene Cl CH3 n Cl Cl Cl Cl Cl Cl Cl Vinyl Chloride Poly(vinyl chloride) F2C CF2 Tetrafluoroethylene F3C F2 C CF 2 F2 C CF 2 F2 C CF 2 F2 C CF 2 F2 C CF 2 F2 C CF 2 CF3 n Poly(tetrafluoroethylene): Teflon
- 15. Condensation/Step Polymerization •Formation of polymers from polyfunctional monomers of organic molecules with elimination of small molecules like water, HCl •Functional group of one monomer unit reacts with functional group of the other •Eg-Nylon-66 (hexamethylenediamine+ adipicacid)
- 16. Polyesters & Amides Monomer Polymer HO2C CO2H HO OH O O HO O H2 C H2 C O n Terephthalic acid Ethylene glycol Poly(ethylene terephthalate H Ester HO OH O O 4 H2N 4 NH2 Adipic Acid 1,6-Diaminohexane Nylon 6,6 HO NH NH H O O 4 4 n HO2C CO2H Terephthalic acid H2N NH2 1,4-Diamino benzene Kevlar O HO O HN HN H n Amide
- 17. Natural Polymers Monomer Polymer Isoprene n Polyisoprene: Natural rubber O H HO H HO H H H OH OH OH Poly(ß-D-glycoside): cellulose O H O H HO H H H OH OH OH H n ß-D-glucose H3N O O R Polyamino acid: protein H3N O HN R1 O HN Rn+1 O OH n Rn+2 Amino Acid Base O OH P O O O O oligonucleic acid DNA Nucleotide Base = C, G, T, A Base O O P O O O O DNA DNA
- 18. Copolymerization •Specific type of addition polymerization, without loss of any small molecules •Monomers of more than one type are involved thereby giving variety of polymers •Eg. Styrene-Butadiene rubber (Buna-S)
- 19. Mechanism •Initiation:Free radicals formed from H2O2through the addition of heat Free radical acts to open the C=C double bond by joining to one side of the monomer. This allows the monomers to react with other open monomers on their other side.
- 20. •Propagation: Process continues with successive addition of monomer units to the chains •Termination: Once the desired polymer is obtained, the polymerization reaction is terminated by combining two chains Mechanism
- 21. Polymer Crystallinity •Polymers are never completely crystallinecrystalline regions with amorphous regions are together •Polymer is crystalline if all molecules are arranged in an orderly manner with symmetrical orientation •Degree of crystallinity depends on DP & tacticity •Crystalline polymers possess high density, sharp melting points, strong, brittle and hard •Amorphous polymers do not possess melting points, but softening points
- 22. Melting and Glass transition temperatures •Lowest temperature beyond which polymer becomes hard, brittle, glass-like or temperature at which polymer experiences transition from rubbery to rigid states is called glass transition temperature (Tg) In this state, solid tends to shatter if it is hit, since the molecular chains cannot move easily. •Temperature above which polymer turns out to be flexible, elastic and rubbery (Tm)
- 23. Beyond glass transition temperature, crystalline and amorphous polymer behaves differently as shown in the diagram below. Effect of heat on polymer
- 24. Significance •Tgand Tmare significant parameters •Gives an indication of the temperature region at which a polymeric material transforms from a rigid solid to a soft viscous state •Helps in choosing the right processing temperature in which materials are converted into finished products
- 25. Factors affecting Tg •Tg is directly proportional to the molecular weight of the polymer. •Greater the degree of cross-linking, higher the Tg. •Polymers with strong intermolecular forces of attraction have greater Tg. •Side groups, especially benzene and aromatic groups attached to main chain increases Tg.
- 26. Number average Molecular weight •Consider a polymer sample in which n1, n2and n3… are number of molecules with molecular weights M1,M2,M3…respectively then, = = Where, ni is number of molecules of mass Mi Molecular Weight
- 27. Number of Molecules, Ni Mass of Each Molecule, Mi Total Mass of Each Type of Molecule, NiMi 1 800,000 800,000 3 750,000 2,250,000 5 700,000 3,500,000 8 650,000 5,200,000 10 600,000 6,000,000 13 550,000 7,150,000 20 500,000 10,000,000 13 450,000 5,850,000 10 400,000 4,000,000 8 350,000 2,800,000 5 300,000 1,500,000 3 250,000 750,000 1 200,000 200,000 Total Mass =NiMi= 50,000,000 NiMi, where Niis the number of molecules of weight Mi Ni= 100 The number average molecular weight for this sample is then, NiMi/ Ni= 50,000,000/100 = 500,000 The number average molecular weight
- 28. Weight Average Molecular Weight •If m1, m2, m3… are masses of the species with molecular weights M1,M2,M3… resp. (m1=n1M1where, n1is number of molecules with molecular weight M1) But, mi=niMi = = = (mi=niMiwhere, niis number of molecules with molecular weight Mi)
- 29. Number of Molecules Mass of Each Molecule Total Mass of EachType of Molecule Weight Fraction (Wi) Type of Molecule (Ni) (Mi) (NiMi) (NiMi/ NiMi) (WiMi) 1 800,000 800,000 0.016 12,800 3 750,000 2,250,000 0.045 33,750 5 700,000 3,500,000 0.070 49,000 8 650,000 5,200,000 0.104 67,600 10 600,000 6,000,000 0.120 72,000 13 550,000 7,150,000 0.143 78,650 20 500,000 10,000,000 0.200 100,000 13 450,000 5,850,000 0.117 52,650 10 400,000 4,000,000 0.080 32,000 8 350,000 2,800,000 0.056 19,600 5 300,000 1,500,000 0.030 9,000 3 250,000 750,000 0.015 3,750 1 200,000 200,000 0.004 800 Weight Average Molecular Weight = WiMi= 531,600 The distribution of molecular weights in a polymer sample is often described by the ratio of the weight average molecular weight to the number average molecular weight. In this case the ratio is 531,600/500,000 = 1.063. This ratio is the PolydispersityIndex (or PDI). Average molecular weight
- 30. •Viscosity Average Molecular weight Where, niis the number of individual molecules having the molecular massMi. Exponenta, between 0.6 and 0.8 for many polymer/solvent systems
- 31. •In 1953, Hermann Staudingerformulated a macromolecular structure for rubber and received the Nobel Prize. isoprene based on the repeating unit 2-methylbuta-1,3-diene Rubber
- 32. Elastomers/ Rubbers •The polymers possessing elasticity to the extent of nearly 200 to 300 percent are known as Elastomers or Rubber •Amorphous polymer with numerous cross linkages and high degree of elasticitydeformed by stretching & regain original form when stretching force is removed •Rubber has no crystallinity. Their extension and contraction are due to temporary movements of segments of polymer chain. The chains do not slip past each other due to cross linkages Unstressed RubberStressed RubberAppliedrelease ofStressstressBack to original position
- 33. Properties of Rubber Important properties of rubber are its •Flexibility •Strength •Impermeability to water •High resistance to abrasion etc, Due to these properties rubber is highly useful for industrial as well as domestic purposes.
- 34. Types of Rubber 1.Natural Rubber-Obtained from natural sources 1.Synthetic Rubber-Made synthetically
- 35. •Raw material from rubber tree (Hevea brasiliensis) is tapped every second day for its sap, known as latex, by making slanting cuts in the bark of the tree. •Latex is collected and acetic acid is added to it so as to precipitate out the rubber, which then hardens/coagulates. •After being washed and dried, rubber is cured in special smokehouses to protect it against microbial attack. •Purer the rubber, higher the grade –it is ready for delivery to rubber companies worldwide. Natural Rubber
- 36. •Natural Rubber •Polymer of isoprene (2-methyl-1,3-butadiene) •Low tensile strength, elasticity over a narrow range of temperature Rubber Destructive distillation Isoprene Dipentene + indicates number of isoprene units. Molecular weight of rubber is very high of about 300,000.
- 37. Structure of Rubber Rubber which is composed of all cis-linked isoprene units, forms an amorphous structure that is highly elastic. On the other hand, guttapercha, which is a polyisoprenecompound made of all trans-linked isoprene units, forms linear strands which can interact into crystalline arrays that have plastic properties, but are not elastic.
- 38. •Its plasticity is greater than elasticity. It can’t sustain stress. Thus when stretched to a great extent, it undergoes deformation permanently. •It has large water absorption tendency, which make it week •Limitations of natural rubber: It softens at high temperature and becomes brittle at low temperature. •Natural rubber is attacked by acids, oxidizing agents, non-polar solvents and oxidized by air. To overcome these limitations rubber is vulcanized. Drawbacks of Natural rubber
- 39. Vulcanization •Vulcanization is a process which is essentially compounding rubber with different chemicals like sulphur, H2S, benzoylchloride etc. •Heating raw rubber with sulphurat 100-140 ˚C. Sulphurenters the double bonds of rubber and forms cross-linkages. Excellent changes in properties, resistance to changes in temperature, increased elasticity, tensile strength, durability, chemical resistance •Brings about stiffening of rubber by anchoring & restricting intermolecular movement by providing cross-linkages between chains.
- 40. Vulcanization
- 41. •The toughness or stiffness of vulcanization depends on the amount of sulphurincluded. •For flexible tyrerubber, sulphurcontent is from 3-5% whereas for tougher variety like ebonite, content of sulphuris 32 %. •Ebonite is so tough that it can be machined and has very good electrical insulation property.
- 42. Property Raw Rubber Vulcanized Rubber Elasticity Very high Low, depending on % S Tensile Strength 200 kg/cm2 2000 kg/cm2 Chemical resistance Very poor Higher Durability Less Higher Quality Inherent Can be controlled by vulcanization
- 43. Applications of rubber •Due to remarkable resistance to electricity, it is used as an insulating coating on wires and cables, used for electric power transmission. •Due to its elasticity, it is used to fabricate rubber bands, rubber goods, golf balls, tubes for automobiles, etc •It acts as an excellent adhesive •Foam-rubber is used for making pillows, cushions, mattresses, automotive pads, etc. •Polysulfide rubber is used as a solid-propellant fuel for rocket motors.
- 44. Preparation, Properties and Uses of Commercial Rubbers
- 45. Copolymerization of butadiene & styrene carried out at 5oC Good and tough mechanical properties Easily attacked by oxidizing agents, mainly ozone, organic solvents Uses: Manufacture of tyres, insulating wires and cables, adhesives, lining of vessels Buna-S Rubber/Cold Rubber Synthetic rubber is any vulcanizableman-made rubber-like polymer which can be stretched to twice its length and on releasing the stress, it returns to its original shape and size.
- 46. Polyurethane (Isocynate) Rubber •Ethylene glycol polymerizes with ethylene diisocyanate to form polyurethane rubber. •Highly resistant to oxidation •Resistant to organic solvents, attacked by acids and alkali Uses: surface coatings and manufacture of foams and fibers
- 47. Theworldconsumptionofsyntheticpolymers :150millionmetrictonsperyear. 1)Plastics:56% 2)Fibers:18% 3)Syntheticrubber:11% 4)CoatingandAdhesives:15% Industrial Polymers
- 48. Plastics ThermoPlastics/Thermosoftening Polymers •Some polymers when heated become soft and can be moulded into any shape that can retain on cooling •PVC, PE, nylon sealing wax, etc Thermosetting polymers •On heating, polymers undergo a chemical change and become an infusible mass which cannot be reshaped •Bakelite, polyester, resins The polymeric materials, which are rigid, dimensionally stable and usually brittle are known as plastic.
- 49. Thermoplasticpolymers Thermosettingpolymers Theysoftenonheatingandhardenoncooling Theyarefusibleoninitialheating,butturnintohardinfusiblemassonheatingfurther Canbereshapedandrecycled Cannotbereshapedandrecycled Formedbyadditionpolymerization Formed by condensation polymerization Linearinstructure Threedimensionalinstructure Theyaresolubleinsomeorganicsolvents Insolubleinorganicsolvents Mouldedarticlesaretakenoutaftercoolingthemouldtoavoiddeformationofthearticle Mouldedarticlesaretakenoutfromthemouldevenwhentheyarehot. e.g.Polyethylene,polystyrene,PVC,PVA e.g.Nylon6:6,Phenolformaldehyde, ureaformaldehyde, Comparisons
- 50. Compounding of Plastics •Unusual for a finished high polymeric articles to solely consist of high polymers alone •Mixed with ingredients known as additivesresulting in useful functions and imparts useful properties to the finished products •Main types of compounding ingredients are –Resin: Binder, which holds different constituents/additives together. Natural or synthetic resins used in this case
- 51. •Plasticizers: Low MW organic liquids added to polymer to improve its flexibility; Added 8-10% of total bulk of plastics (oils, camphor, dioctylphthalates)The small molecules penetrate into the polymer matrix and neutralize a part of intermolecular forces of attraction between macromolecules and increase mobility of polymer segments so that chains can slide over each other. Hence, plasticizers act as an internal lubricant
- 52. •Stabilizers: Most polymers do not possess chemical stabilitychange colors & decompose –Stabilizers are additives which chemically stabilize the polymer and thus arrest degradation –Organic, inorganic, organometallic compounds like CaO, BaO, Organo-tin compounds •Fillers/Extenders: Inert material added to enhance mechanical strength--asbestos powder, saw dust, cotton pulp, clay, etc •Lubricants: Glossy finish to product, Prevents plastics from sticking to fabrication equipments; oils, waxes, soaps, etc
- 53. •Catalysts Antioxidants like H2O2, benzoyl peroxide, ZnO, NH3, Ag, Pb, are added to the polymeric matrix to accelerate the cross linking in thermosetting plastics while moulding process •Coloring materials Organic dyes and pigments impart desired color for aesthetic appeal of the finished polymeric material. Some colors are added to impart UV protection to the finished products.
- 54. Preparation, Properties and Uses of Commercial Plastics
- 55. Phenol Formaldehyde Resin Acid or a base as a catalyst to undergo condensation polymerization product nature depends on the catalyst and ratio of phenol and formaldehyde. Novolacresin is a linear thermoplastic polymer, whereas Bakelite is a cross-linked thermosetting polymer.
- 57. Properties and Uses •Phenolic resins are rigid, hard, water resistant •Resistant to acids, salts, organic solvents •Easily attacked by alkalies due to the presence of free hydroxy groups •Possess electrical insulating properties due to low thermal conductivity •Uses: –Used to fabricate insulators, plugs, switches –Used as cation-exchanger resin in water softening –Adhesives in paints and varnishes –Propellar shafts for paper industry and mills
- 58. Poly(methyl methacrylate)(PMMA) •Poly(methyl methacrylate)(PMMA) is a transparent thermoplastic often used as a lightweight or shatter- resistant alternative toglass. •Although it is not technically a type of glass, the substance has sometimes historically been calledacrylic glass. •Chemically, it is the synthetic polymerofmethyl methacrylate.
- 59. Property
- 60. Applications of PMMA Safety glass such as Plexiglassand Lucite –uses range from windows for aquariums and under- water restaurants to safety shields at hockey rinks to skylights in your home to simple paperweights Used as bone cement for use in arthroplasticprocedures of the hip, knee, and other joints for the fixation of polymer or metallic prosthetic implants to living bone Used in Pacemakers Artificial eye lenses used for cataract surgery
- 61. Urea formaldehyde resin Monomethylolurea on polymerization, yields a linear UF resin polymer
- 63. •Urea-formaldehyde resin yields clear, water-white products. •Hardness, tensile strength is comparatively better than phenolic resins •Better heat & moisture resistance Uses: •Adhesives for plywood, decorative laminates-surface coatings •Due to their colorability, solvent, grease resistance cosmetic containers •Electrical insulation
- 64. Conducting Polymers •Polymers are poor conductors of electricity, due to non- availability of large number of free electrons •The polymeric material which possess electrical conductivities on par with metallic conductors known as conducting polymer. •Polymers with polyconjugatedstructures are insulators in pure state, but when treated with oxidizing or reducing agents can be converted into polymer salts with electrical conductivities comparable to metals.
- 65. What makes the material conductive? Diamond, which contains only σ bonds, is an insulator and its high symmetry gives it isotropic properties. Graphite and acetylene both have mobile π electrons and are, when doped, highly anisotropic metallic conductors.
- 66. Conducting polymers are classified as •π-electron conducting polymers: In these polymers, backbone of the polymer is made up of molecules that contain conjugated π-electrons which extend the entire polymer and make the polymer conducting. •Conducting element-filled polymer: Here, polymer acts as a binder that binds the conducting elements like carbon black, metal oxides, metallic fibresthat conduct electricity. •Inorganic polymer: A metal atom with polydentateligand, which is a charge transfer complex is bound to the polymer to make it conducting. •Doped-conducting polymer: Polymer is made conducting by exposing the surfaces to charge transfer agents in gas or in solution phase. •Blended conducting polymer: This polymer is made by blending a conventional polymer with a conducting polymer. Types of conducting polymers
- 67. Conditions •Polymer should consist of alternating single and double bonds called conjugated double bonds •Polymer matrix has to be disturbed – –Either by removing electrons from them (oxidation), –Or inserting electrons into the material (reduction). The process is known as doping –By doping with electron donor like alkali-metal ion or electron acceptor like AsF5, Iodine, etc polymers turn conductive materials
- 68. Fistconditionsto becomeconductive: 1-The firstconditionforthisisthatthepolymerconsistsof alternatingsingle and doublebonds, calledconjugateddoublebonds. In conjugation, thebondsbetweenthecarbonatomsare alternatelysingle and double. Everybond containsa localised“sigma” (σ) bond whichformsa strongchemicalbond. In addition, everydoublebond alsocontainsa lessstronglylocalised“pi” (π) bond whichisweaker.
- 69. 2-The second condition is that the plastic has to be disturbed - either by removing electrons from (oxidation), or inserting them into (reduction), the material. The process is known as Doping. • There are two types of doping: 1-oxidation with halogen (or p-doping). 2- Reduction with alkali metal (called n-doping). CH xNa CH xNa x n n 3 2 3 I CH I x CH n n 2nd conditions to become conductive:
- 70. •Iodine molecule attracts an electron from polyacetylene chain and becomes I3- •Polyacetylene molecule, now positively charged, is termed a radical cation, orpolaron •Lonely electron of the double bond, from which an electron was removed, can move easily. •As a consequence, double bond successively moves along the molecule–Conducting Polymers
- 71. Polypyrrole •Hetero atomic polymers •More stable •Easy to prepare •Greater opportunity to functionalize
- 72. Polypyrole
- 73. Conducting Polymers Telecommunication Aerospace Battery technology Smart Materials Applications
- 74. Self healing polymers •Inspired from biological systems ‘Wound healing’ •Inherent ability of polymers to repair damage caused by mechanical usage over time •Terminator Polymers •Chemistry World posted a video of the product in action, showing someone cutting a piece of the polymer in two with a scalpel, pressing the pieces back together and leaving it on a table for two hours at room temperature. The person is unable to pull the material apart with their hands upon returning. •This is the next generation breakthrough in polymers.
- 75. •Autonomic healing: A propagating crack ruptures the microcapsules, releasing the healing agent into the crack plane by capillary action. Polymerization is initiated by contact with the embedded catalyst or initiator, bonding the crack faces, and restoring structural continuity.
- 76. •Non-autonomic healing: Partially self- contained; healing capability is designed into the material, but additional external stimuli such as heat or UV-radiation is required for the healing to occur.
- 77. Applications •Nissan Motor Co. Ltd has commercialized world’s first self-healing clear coat for car surfaces-trade name of this product is ‘Scratch Guard Coat’ •Self healing concretes–in progress •Self-healing materials are now used as composites in aircrafts.
- 78. Thank you