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Presentation on theme: "Polymers."— Presentation transcript:

1 Polymers

2 Introduction to Polymers
Poly = many, mer = unit, many units Polymer 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”. OR polymer 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 chain NATURAL POLYMER SYNTHETIC POLYMER Collagen Gelatin Silk Wool Natural rubber DNA Polyethylene terephthalate (PET) High Density Polyethylene (HDPE) Polyvinyl Chloride (PVC) Low Density Polyethylene (LPDE) Polypropylene (PP) Polystyrene (PS)

8 Examples Of Polymers Polypropylene (PP) - Carpet, upholstery
Polyethylene low density (LDPE) - Grocery bags Polyethylene high density (HDPE) - Detergent bottles, toys Poly(vinyl chloride) (PVC) - Piping, decking Polystyrene (PS) - Toys, foam Polytetrafluoroethylene (PTFE, Teflon) - non-stick pans, electrical insulation Poly(methyl methacrylate) (PMMA, Lucite, Plexiglas) - Face shields, skylights Poly(vinyl acetate) (PVAc) - Paints, adhesives Polychloroprene (cis + trans) (Neoprene) - Wetsuits

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 strength and 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
Reflective Impact resistant Tough Brittle Translucent Malleable Soft Elastic Inelastic Insulative

12 source structure Polymerization Molecular force
Classification of Polymer is based on source structure Polymerization Molecular force

13 Classification based on Source
Natural polymers Semi-synthesis polymers Synthesis polymers

14 Natural polymers The 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 importance Cellulose, 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 silk chemically treated polymers, that are of natural origin termed as semi synthesis

16 Synthesis polymers Synthetic 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 structure Linear polymers Branched chain polymers Cross 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 straight As the polymer chain grows, it folds back on itself in a random fashion E.g Polyethylene

19 Branched chain polymers
Polymers with branches at irregular intervals along the polymer chain are called branched polymers difficult for the polymer molecules to pack in a regular array less crystalline and less dense amount and type of branching also affects physical properties such as viscosity and elasticity Branches often prevent chains from getting close enough together for intermolecular forces to work effectively. E.g. polyethylene PE 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 bonds contain 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

21 Based on polymerization
additional condensation

22 Addition polymers formed by the repeated addition of monomer molecules possessing double or triple bonds n(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
nylon thermoplastic thermosetting

25 Nylon Nylon 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 acids A 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 6,6 nylon-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: bakelite bakelite: 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 Science Plastic containers of all shapes and sizes are light weight and economically less expensive than the more traditional containers. Clothing floor coverings garbage disposal bags packaging are other polymer applications.

31 Industry Automobile parts windshields for fighter planes Pipes Tanks
packing materials insulation, wood substitutes elastomers 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 Polymers In general, the longer the polymer chain, the stronger the polymer. There are two reasons for this: longer chains are more tangled there 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.


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