2 Introduction to Polymers Poly = many, mer = unit, many unitsPolymer science is relatively a new branch of science . It deals with chemistry physics and mechanical properties of macromolecule .
3 A polymer is a large molecule which is formed by repeated linking of the small molecules called “monomers”.ORpolymer is organic substance made up of many repeating units or building blocks of molecules called mers.
4 Combine, many monomers to create a polymer. Polymer is often used as a synonym for ‘plastic’.All plastic are polymers, but not all polymers are plastics.Poly mers are made up of many Mono mer↓ ↓ ↓ ↓Many Units One Unit
5 Monomer molecules joined in units of long polymer.
6 It consist of large no. of repeating units known as monomers The no. of repeating units in a chain of polymer is known as degree of polymerization
7 POLYMER a family of natural and synthetic materials made of repetition of high weight molecules in a form of flexible chainNATURAL POLYMERSYNTHETIC POLYMERCollagenGelatinSilkWoolNatural rubberDNAPolyethylene terephthalate (PET)High Density Polyethylene (HDPE)Polyvinyl Chloride (PVC)Low Density Polyethylene (LPDE)Polypropylene (PP)Polystyrene (PS)
9 Characteristics of Polymers Low Density.Low coefficient of friction.Good corrosion resistance.Good mould ability.Excellent surface finish can be obtained.Can be produced with close dimensional tolerances.Economical.Poor tensile strength.Low mechanical properties. Poor temperature resistance. Can be produced transparent or in different colours.
10 Properties of Polymers The physical properties of a polymer, such as its strengthand flexibility depend on:Chain length - in general, the longer the chains the stronger the polymer;Side groups - polar side groups give stronger attraction between polymer chains, making the polymer stronger;Branching - straight, un branched chains can pack together more closely than highly branched chains, giving polymers that are more crystalline and therefore stronger;Cross-linking - if polymer chains are linked together extensively by covalent bonds, the polymer is harder and more difficult to melt.
11 Properties of Polymers ReflectiveImpact resistantToughBrittleTranslucentMalleableSoftElasticInelasticInsulative
12 source structure Polymerization Molecular force Classification of Polymer is based onsourcestructurePolymerizationMolecular force
13 Classification based on Source Natural polymersSemi-synthesis polymersSynthesis polymers
14 Natural polymersThe definition of a natural polymer is a polymer that results from only raw materials that are found in nature.Example:-Proteins,Cellulose,Starch,Rubber.
15 Semi-synthesis polymers chemically treated polymers of natural origin are quite common and of great practical importanceCellulose, for example, is used in two different ways:it is dissolved using some special solvent and precipitated again in a different physical shape, e.g.viscose silk (reyon)copper silkchemically treated polymers, that are of natural origin termed as semi synthesis
16 Synthesis polymersSynthetic polymers are derived from petroleum oil, and made by scientists and engineers.Examples of synthetic polymers include nylon,polyethylene,polyester,Teflon, and epoxy.
17 Branched chain polymers Cross linked chain polymer Based on structureLinear polymersBranched chain polymersCross linked chain polymer
18 Linear polymers consists of a long string of carbon-carbon bonds misleading because the geometry around each carbon atom is tetrahedral and the chain is neither linear nor straightAs the polymer chain grows, it folds back on itself in a random fashionE.gPolyethylene
19 Branched chain polymers Polymers with branches at irregular intervals along the polymer chain are called branched polymersdifficult for the polymer molecules to pack in a regular arrayless crystalline and less denseamount and type of branching also affects physical properties such as viscosity and elasticityBranches often prevent chains from getting close enough together for intermolecular forces to work effectively.E.g. polyethylenePE is a relatively simple polymer, there are two common forms of it (high and low-density,) each with unique properties.
20 Cross linked chain polymers formed from bi-functional and tri- functional monomers and contain strong covalent bondscontain short side chains (cross links)connect different polymer chains into a “network”adding cross-links between polymer chains makes the polymer more elastic (they can stretch and return to their original form)Cross links between chains
22 Addition polymersformed by the repeated addition of monomer molecules possessing double or triple bondsn(CH2=CH2) (CH2 -CH2 )-Ethylene polyethylene
23 Condensation polymers formed by repeated condensation reaction between two different bi- functional or tri-functional monomeric units.eg. terylene (dacron), nylon 6, 6, nylon 6.n(H2N(CH2)6 NH2) + n(HOOC(CH2)4COOH) [-NH(CH2)6NHCO(CH2)4CO-]n + nH2O (Nylon 6:6)
24 Based on molecular force nylonthermoplasticthermosetting
25 NylonNylon is used as general name for all synthetic fiber forming polyamides, i.e., having a protein like structure.These are the condensation polymers of diamines and dibasic acidsA number is usually suffixed with the Nylon which refers to the number of carbon atoms present in the diamine and the dibasic acids respectively.example: nylon 6,6nylon-6,6: Nylon-6,6 is obtained by the polymerisation of adipic acid with hexamethylene diamine.
26 Thermoplastic polymers These are linear or slightly branched long chain polymers, which can be softened on heating & reversibly hardened on cooling repeatedly.Their hardness is a temporary property & varies with temperature.Example:- polyvinyl chloride.Polyvinyl chloride:- It is a vinyl polymer constructed of repeating vinyl groups (ethenyls) having one of their hydrogens replaced with a chloride group.
27 Thermosetting polymers initial mixture of reactive, low molar mass compounds reacts upon heating in the mold to form an insoluble, infusible network. Example: bakelitebakelite: bakelite is formed of phenol and form-aldehyde polymerization.
28 Applications of Polymers: Polymeric materials are used in and on soil to improve aeration, provide mulch, and promote plant growth and health.
29 Medicine Many biomaterials; heart valve replacements blood vessels, are made of polymers like Dacron, Teflon and polyurethane.
30 Consumer SciencePlastic containers of all shapes and sizes are light weight and economically less expensive than the more traditional containers.Clothingfloor coveringsgarbage disposal bagspackaging are other polymer applications.
31 Industry Automobile parts windshields for fighter planes Pipes Tanks packing materialsinsulation, wood substituteselastomers are all polymer applications used in the industrial market.
32 Sports Playground equipment various balls golf clubs swimming pools protective helmets are often produced from polymers.
33 Strength of PolymersIn general, the longer the polymer chain, the stronger the polymer. There are two reasons for this:longer chains are more tangledthere are more intermolecular forces between the chains because there are more points of contact. These forces, however, are quite weak for polyethene.Areas in a polymer where the chains are closely packed in a regular way are said to be crystalline. The percentage of crystallinity in a polymer is very important in determining its properties. The more crystalline the polymer, the stronger and less flexible it becomes.
34 When a polymer is stretched (cold-drawn), a neck forms When a polymer is stretched (cold-drawn), a neck forms. In the neck the polymer chains line up producing a more crystalline region. Cold-drawing leads to an increase in strength.The first polyethene which was made contained many chains which were branched. This resulted in a relatively disorganised structure of low strength and density. This was called low density polyethene (ldpe).In the crystalline form, the methyl groups all have the same orientation along the chain. This is called the isotactic form. In the amorphous form, the methyl groups are randomly orientated. This is called the atactic form.Polymers with a regular structure are said to be stereoregular.