3 INTRODUCTIONThe word polymer is derived from Greek words “poly” means many and “mer” means unit or part.Polymers are generally macromolecules formed by the repeated linking of large number of small molecules.Polymers are widely used in automobiles, defence, electrical goods and computer components etc.
4 PolymersPolymers are macro molecules (giant molecules of higher molecular weight) formed by the repeated linking of large number of small molecules called monomers.Polyethylene is a polymer formed by the repeated linking of large number of ethylene molecule.
5 MonomerMonomer is a micro molecule (small molecule) which combines with each other to form a polymer.Some monomers and repeating unit of the polymers are given below.
12 POLYMERISATIONPolymerisation is a process in which large number of small molecules (called monomers) combine to give a big molecule (called a polymer) with or without elimination of small molecules like water.
13 Degree of Polymerization (DP) The number of repeating units (n) in a polymer chain is known as degree of polymerisation. It is represented by the following relationship.molecular weight of the polymeric networkDegree of polymerization (n)molecular weight of the repeating unit
14 In this example, five repeating units are present in the polymer chain In this example, five repeating units are present in the polymer chain. So, the degree of polymerization is 5.
15 OligomersPolymers with low degree of polymerisation are known as Oligomers, their molecular weight ranges fromHigh PolymersPolymers with high degree of polymerisation are known as High polymers, their molecular weight ranges from 10, ,00,000.
16 FUNCTIONALITY AND ITS SIGNIFICANCE The number of bonding sites or reactive sites or functional groups, present in a monomer, is known as its functionality.
18 Significance 1. Bifunctional Monomers Bifunctional monomers (i.e., functionality of the monomer is 2) mainly form linear (or) straight chain polymer.Each monomeric unit in the linear chain is linked by strong covalent bonds (primary bonds), but the different chains are held together by weak vander waal’s forces of attraction (secondary bonds).Therefore, there is no restriction to movement of one chain over another.This type of polymers are soft and flexible, and possess less strength, low heat resistance.These are soluble in organic solvents.
20 2. Trifunctional Monomers When a trifunctional monomer (i.e., functionality of the monomer is 3) is mixed in small amounts with a bifunctional monomer, they form branched chain polymer.The movement of polymer chain in branched polymer is more restricted than that of straight chain polymers.
22 3. Polyfunctional Monomers Poly functional monomers form cross-linked polymer(three-dimensional network polymer).All the monomers in the polymer are connected to each other by strong covalent bonds.Therefore the movement of polymer chain is totally restricted.This type of polymers are hard and brittle and possess very high strength and heat resistance.They are insoluble in almost all organic solvents.
26 I. Natural PolymersThe polymers obtained from nature (plants and animals) are called natural polymers.
27 It is a polymer of glucose. It is a chief food reserve of plants. EXAMPLES OF NATURAL POLYMERS1. StarchIt is a polymer of glucose. It is a chief food reserve of plants.2. CelluloseIt is also a polymer of glucose. It is a chief structural material of the plants. Both starch and cellulose are produced by plants during photosynthesis.
28 These are polymers of amino acids. 3. ProteinsThese are polymers of amino acids.They have generally 20 to 100 amino acids joined together in a highly organized arrangement.These are building block of animals.
29 These are polymers of various nucleotides. RNA and 4. Nucleic AcidsThese are polymers of various nucleotides. RNA andDNA are common nucleotides.5. Natural RubberIt is a polymer of unsaturated hydrocarbon, 2-methyl-1, 3 butadiene, called isoprene. It is obtained from latex of rubber trees.
31 II. Synthetic PolymersThe polymers which are prepared in the laboratories, are called synthetic polymers. These are also called man-made polymers.PVC, polyethylene, nylon, teflon, bakelite, terylene, etc.,
32 Types of Synthetic Polymers 1. Organic PolymersThese are polymers containing hydrogen, oxygen, nitrogen, sulfur and halogen atoms apart from carbon atoms.Polyethylene, Polyvinyl alcohol, PVC,Epoxy polymers, Polyurethane.
33 2. Elemento-organic (or) Hetero-organic Polymers These are polymers composed of carbon atoms and hetero-atoms (like N, S & O).The main chain consists of carbon atoms and whose side groups contain hetero atoms linked directly to the C atoms in the chain.Polysiloxanes, Polytitoxanes
34 3. Inorganic PolymersThese are polymers containing no carbon atoms.The chains of these polymers are composed of different atoms joined by chemical bonds.
36 PLASTICSPlastics are high molecular weight organic materials, that can be moulded into any desired shape by the application of heat and pressure in the presence of a catalyst.
37 Originally, plastics were discovered and then Originally, plastics were discovered and then developed based on trial and error method.The present time is sometime referred as plastic age, because the use of polymeric material is perculated in large variety of applications.This rapid growth has taken place only in the last 50 years.It was man’s desire to develop plastics for engineering applications to replace, glass, metal, ceramic, wood and other materials of constructions.Since plastics possess the following advantages, they have wider applications.
38 Advantages of Plastics Over other Materials They are light in weight.They possess low melting point.They can be easily moulded and have excellent finishing.They possess very good strength and toughness.They possess good shock absorption capacity.They are corrosion resistant and chemically inert.They have low co-efficient of thermal expansion and possess good thermal and electrical insulating property.They are very good water-resistant and possess good adhesiveness.
39 Disadvantage of Plastics Softness.Embrittlement at low temperature.Deformation under load.Low heat-resistant and poor ductility.Combustibility.Degradation upon exposure to heat and UV- radiation.Non bio-degradable.
40 Classification of Plastics Based on the structure and type of resin used for the manufacture of plastics, plastics are classified into two main types.1. Thermoplastics.2. Thermosetting plastics.A resin is a basic binding material, present in plastics, which undergoes polymerization reaction during moulding.
42 Thermoplastics are prepared by addition polymerisation. They are straight chain (or) slightly branched polymers and various chains are held together by weak vanderwaal’s forces of attraction.Thermoplastics can be softened on heating and hardened on cooling. They are generally soluble in organic solvents.
44 Thermosetting plastics are prepared by condensation polymerisation. 2.Thermosetting Resins (or) ThermosetsThermosetting plastics are prepared by condensation polymerisation.Various polymer chains are held together by strong covalent bonds (called crosslinks).Thermosetting plastics get harden on heating and once harden, they cannot be softened again.They are almost insoluble in organic solvents.
48 TYPES OF POLYMERISATION Polymerisation reactions may be carried out by any one of the following methods.1. Addition (or) chain growth polymerisation2. Condensation (or) step wise polymerisation3. Copolymerisation
49 1. Addition (or) Chain Growth Polymerisation It is a reaction that yields a polymer, which is an exact multiple of the original monomeric molecule.The original monomeric molecule, usually, contains one or more double bonds.In this addition polymerisation there is no elimination of any molecule.
56 3. Co-polymerisationIt is the joint polymerisation in which two (or) more different monomers combine to give a polymer.High molecular weight polymers, obtained by co-polymerisation, are called copolymers Copolymerisation is mainly carried out to vary the properties of polymers such as hardness, strength, rigidity, heat resistance etc.
61 Mechanism of Addition Polymerisation The mechanism of addition polymerisation can be explained by any one of the following types.1. Free radical mechanism2. Ionic mechanismAll the above mechanisms occur in three major steps namely,i. Initiationii. Propagation andiii. Termination
62 Free Radical Mechanism 1. InitiationIt is considered to involve two reactions.(a) First reaction; It involves production of free radicals by homolytic dissociation of an initiator (or catalyst) to yield a pair of free radicals R.
63 Examples of some commonly used thermal initiators Thermal initiator is a substance used to produce free radicals by homolytic dissociation at high temperature.
65 (b). Second reaction; It involves addition of this free radical to the (b). Second reaction; It involves addition of this free radical to the first monomer to produce chain initiating species.
66 2. PropagationIt involves the growth of chain initiating species by successive addition of large number of monomers.The growing chain of the polymer is known as living polymer.
67 3.TerminationTermination of the growing chain of polymer may occur either by coupling reaction or disproportionation.(a) Coupling (or) CombinationIt involves coupling of free radical of one chain end to another free radical forming a macromolecule
68 The product of addition polymerisation is known as Dead polymer. (b) DisproportionationIt involves transfer of a hydrogen atom of one radical centre to another radical centre, forming two macromolecules, one saturated and another unsaturated.The product of addition polymerisation is known as Dead polymer.
69 IONIC MECHANISM (or) IONIC POLYMERISATION Ionic polymerisation is faster than the free radical polymerisation. Ionic polymerisation is initiated by a positiveion (cation) or a negative ion (anion). Depending upon the nature of ions (initiators) the ionic polymerisation takes place in two ways.1. Cationic polymerisation (or) Carbonium ion mechanism.2. Anionic polymerisation (or) Carbanion mechanism.
70 1.Cationic polymerisation This type of polymerisation takes place when electron donating groups like CH3, C6H5 are present in a monomer.These groups stabilise the carbonium ion formation.Styrene, Isobutylene, Isoprene.The catalysts (initiators) used to initiate the reaction are Lewis acids like AlCl3, BF3 with a co-catalyst water.
71 (i) InitiationIt involves the formation of chain initiating species
72 (ii) PropagationIt involves the growth of chain initiating species by successive addition of large number of monomers and the positive charge simultaneously shifts to the newly added monomer.
74 2.Anionic Polymerization This type of polymerization takes place when electron withdrawing groups like Cl-, CN- are present in a monomer. These groups stabilise the carbanion formation.Vinyl chloride, Styrene, Acrylonitrile.The catalysts (initiators) used to initiate the reaction areLewis bases like NaNH2, KNH2, LiNH2 etc.,
75 It involves the formation of chain initiating species. (i) InitiationIt involves the formation of chain initiating species.
76 (ii) PropagationIt involves the growth of chain initiating species by successive addition of large number of monomers and the negative charge simultaneously shifts to the newly added monomer.
77 Termination of the growing chain occurs by adding ammonia. (iii) TerminationTermination of the growing chain occurs by addingammonia.
78 Properties of Polymers 1. Glass transition temperature (Tg)Glass transition temperature (Tg) is the temperature at which the amorphous solid state is transformed to the melt state.Below the glass transition temperature (Tg) the polymer is hard and above which it is soft.The hard brittle state is called as glassy state and the soft flexible state is called as rubbery or viscoelastic state.Thus the glass transition temperature is an important property of a polymer and it decides whether the polymer behave like glass or rubber.
80 Below Tg the polymer is hard and brittle (like glass). Factors influencing TgThe value of Tg depends on (a) chain-length (b) extent of cross-linking (c) the barrier which hinders the internal rotation of the chain links.The value of Tg of a given polymer varies with the rate of heating or cooling.Below Tg the polymer is hard and brittle (like glass).4. Tg of a liner polymer is sharp, because of the free movement of polymer chains (chains are held by weak vanderWaals forces).5. A cross-linked polymer does not possess any Tgbecause polymer chains will not move.Thus the polymers with a symmetrical structure are crystalline, while the polymers with irregular chain back bone are amorphous.
81 2. Stereospecific Polymer (or) Tacticity The orientation of monomeric units or functional groups in a polymer molecule can take place in an orderly (or) disorderly manner with respect to the main chain is known as Tacticity.Tacticity do affect the physical properties of the polymer.This orientation results in three types of stereo- regular polymers.
82 a. Isotactic PolymerIf the functional groups are arranged on the same side of the main chain, the polymer is called Isotactic polymer.
83 b. Syndiotactic Polymer If the functional groups are arranged in an alternating fashion, the polymer is called Syndiotactic polymer.
84 c. Atactic PolymerIf the functional groups are arranged randomly, thepolymer is called Atactic polymer.
85 Molecular - Mass of Polymer solution, softening temperature, tensile and impact strength and heat resistance are influenced by molecular-mass.Generally low molecular weight polymers are soft and gum-like resins.The high molecular weight polymers are tougher and more heat resistant.Thus, control of molecular weight of polymers is very important for industrial polymerization.Therefore, determination of molecular weight is of greater importance.
86 The molecular weight of polymers depends on the type of monomers involved in polymerization reactions.The final product will contain the macromolecules of different masses.Most of the polymers are polydisperse i.e.., the molecules of polymers do not have identical molecular weight (M).So it is necessary to take average molecular mass.
92 Weight average molecular mass not only Weight average molecular mass not only depends on the number of particles, but also on the molecular size.Hence, in the averaging process, molecular weight of each individual species in multiplied by the mass and not by the number. i.e.,
99 Determination of Molecular Masses The molecular masses of a polymer can be determined by the following methods.1. Measuring colligative properties such as osmometry, ebullioscopy and cryoscopy2. Light scattering measurements.3. Measuring viscosities of polymer solutions.4. By end group chemical analysis.5. By ultracentrifuge.
100 TECHNIQUES OF POLYMERIZATON The following methods are generally used for the polymerisation reaction1. Bulk polymerisation.2. Solution polymerisation.3. Suspension polymerisation.4. Emulsion polymerisation
101 1. Bulk PolymerisationBulk polymerisation is the simplest method of polymerisation. The monomer is taken in a flask as a liquid form and the initiator, chain transfer agents are dissolved in it.The flask is placed in a thermostat under constant agitation and heated.
102 The reaction is slow but becomes fast as the temperature rises. After a known period of time, the whole content is poured into a methanol (non-solvent) and the polymer is precipitated out.Polystyrene, PVC, PMA are preparedby this method
103 Advantages 1. It is quite simple and requires simple equipments. 2. Polymers are of high-purity obtained.3. As the monomer is solvent, excess monomer canbe removed by evaporation.4. The polymer has high optical clarity.
104 Disadvantages1. During polymerisation, viscosity of the medium increases hence mixing and control of heat is difficult.2. Polymerisation is highly exothermic
105 Applications1. The polymers obtained by this method are used in casting formulations.2. Low molecular weight polymers, obtained by this method, are used as adhesives, plasticizers and lubricant additives
106 2. Solution Polymerisation In solution polymerisation, the monomer, initiator and the chain transfer agents are taken in a flask and dissolved in an inert solvent.The whole mixture is kept under constant agitation.After required time, the polymer produced is precipitated by pouring it in a suitable non- solvent.
108 The solvent helps to control heat and reduces viscosity built up. Polyacrylic acid, polyisobutylene and polyacrylonitrile are prepared by this method.
109 Advantages1. Heat control is easy.2. Viscosity built up is negligible.3. The mixture can be agitated easily
110 Disadvantages1. The removal of last traces of solvent is difficult.2. This polymerization requires solvent recovery and recycling.3. It is difficult to get very high molecular weight polymer.4. The polymer formed must be isolated from the solution either by evaporation of the solvent or by precipitation in a non-solvent.
111 ApplicationsAs the polymer is in solution form, it can be directly used as adhesives and coatings.
112 3. Suspension Polymerisation Suspension polymerisation is used only for water insoluble monomers.This polymerisation reaction is carried out in heterogeneous systems.At the end of polymerisation, polymer is separated out as spherical beads or pearls.This method is also called pearl polymerisation.
113 The water insoluble monomer is suspended in water The water insoluble monomer is suspended in water tiny droplet and a initiator is dissolved in it by continuous agitation.The suspension (droplets) is prevented from coagulation by using suspending agents like PVA, gelatin, methyl cellulose. Each droplet of the monomer contains dissolved initiator.The whole content is taken in a flask and heated at constant temperature with vigorous agitation in a thermostat with nitrogen atmosphere. After the end of 8 hrs, pearl-like polymers are obtained, which is filtered and washed by water.
115 Advantages1. Since water is used as a solvent, this method is more economical.2. Products obtained is highly pure.3. Isolation of product is very easy.4. Efficient heat control.5. Viscosity build up of polymer is negligible.
116 Disadvantages1. This method is applicable only for water insoluble monomers.2. Control of particle size is difficult.
117 Applications 1. Polystyrene beads are used as ion exchangers. 2. This technique is used in heterogeneous system.
120 Advantages1. The rate of polymerisation is high.2. Heat can be easily controlled and hence viscosity built up is low.3. High molecular weight polymer can be obtained
121 Disadvantages1. Polymer needs purification.2. It is very difficult to remove entrapped emulsifier and de-emulsifiers.3. It requires rapid agitation.
122 Applications1. Emulsion polymerisation is used in large- scale production like water-based paints, adhesives, plastics, etc.,2. This method is also suitable for manufacturing tacky polymers like butadiene and chloroprene.
127 Properties of Nylon-6(i) Nylon-6 is a light weight, soft and less stiff material.Its melting point is 2250C.
128 General Properties of Nylons (i) They behave as plastic as well as fiber.(ii) They are translucent, white, horny and high melting polymers.(iii) They are insoluble in common organic solvents but soluble in phenol and formic acid.(iv) They possess good mechanical properties and fairly resistant to moisture.(v) They are characterised by combination of high strength, elasticity, toughness and abrasion resistance. `
129 Uses of Nylons(i) Nylon-6:6 is used for fibers, which are used in making socks, ladies shoes, dresses, carpets, etc,.(ii) Nylon-6 is mainly used for moulding purposes for gears, bearings, electrical mountings, etc,. Nylon bearings work without any lubrication.(iii) Nylons are used for making filaments for ropes, bristles for tooth-brushes, films and tyre-cords
130 II. Epoxy Resins (or) Epoxide Polymers These are cross-linked thermosetting resins.They are polyethers because the monomeric units in the polymer have an ether type of structure i.e., R - O - R.
131 PreparationEpoxy polymer (or) Epoxy resins are prepared by condensing epichlorohydrin with bisphenol.The reactive epoxide and hydroxyl groups give a three dimensional cross-linked structure.The value of n ranges from 1 to 20.
133 Properties. Due to the presence of stable ether linkage, epoxy resin possess high chemical- resistance to water, acids, alkalis, various solvents and other chemicals.. They are flexible, tough and possess very goodheat resisting property.. Because of the polar nature of the molecules, they possess excellent adhesion quality.
134 UsesEpoxy resins are used as surface coatings, adhesives like araldite, glass-fibre- reinforced plastics.These are applied over cotton, rayon and bleached fabrics to impart crease-resistance and shrinkage control.These are also used as laminating materials in electrical equipments.Moulds made from epoxy resins are employed for the production of components for aircrafts and automobiles.