1. Polymers

2. Polymers
A macromolecule is a very large molecule consisting of repeating units called monomers. These structural units are bound together by covalent bonds. A collection of macromolecules is called a polymer. For example, polyethylene
Unsaturated
Saturated

3. General Characteristics of Polymers
Low Density.
Low coefficient of friction.
Good corrosion resistance.
Good mould ability.
Excellent surface finish can be obtained.
Can be produced transparent or in different colors.
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.
Cross-linking - if polymer chains are linked together extensively by covalent bonds, the polymer is harder and more difficult to melt.
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4. Polymers can be very resistant to chemicals.
Polymers can be both thermal and electrical insulators
Generally, polymers are light in weight with varying degrees
of strength.
Polymers can be processed in various ways to produce
thin fibers or intricate parts.

5. Polymerization
Polymers are prepared by polymerizing a monomer. The reaction is called polymerization
Polymerization of ethylene to form polyethylene
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6. Classification of polymers
a. Natural and Synthetic Polymers: Origin
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7. b. Thermoplastic and thermosetting polymers: Thermal Response
Molecules in a thermoplastic are held together by relatively weak intermolecular forces so that the material softens when exposed to heat and then returns to its original condition when cooled. Example of such polymers are Polyolefins, nylons, linear polyesters and polyethers, PVC, sealing wax etc.
Thermosetting:
A thermosetting plastic, or thermoset, solidifies or "sets" irreversibly when heated. For example, Phenolic, resins, urea, epoxy resins, diene rubbers, etc.

8. Types of Polymerization
c. Mode of formation
Types of Polymerization
Addition (Chain) Polymerization
Monomers add successively to a growing polymer chain
Polyethylene and polystyrene are addition polymers.
Condensation (Step) Polymerization
Polymer chain grows when monomers combine and split out water or other small molecule.
Nylon and polyurethane are condensation polymers.
Copolymerization
A copolymer is a polymer that has two types of monomer units in its chain .

9. Fig. Examples of addition polymers.
Addition and Condensation Polymer: Mode of Formation
Addition polymers:- They are formed from olefinic, diolefinic, vinyl and related monomers. They are formed from simple addition of monomer molecules to each other in a quick succession by a chain mechanism. This process is called addition polymerization. Examples of such polymers are polyethylene, polypropylene, polystyrene.
Fig. Examples of addition polymers.

10. Addition Polymerization
In this type of polymerization C=C bonds of monomers react to form larger monomers until the unit is a larger polymer chain as seen here.
Table on the next slide shows ethylene monomer based polymers
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11. Table: Polymers Derived from Modified Ethylene Monomers
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13. Condensation polymers:- They are formed from intermolecular reactions between bifunctional or polyfunctional monomer molecules having functional groups such as –OH, COOH, -NH2, NCO etc.

15. Fig. Atactic, isotactic and syndiotactic polymers.
Atactic, isotactic and syndiotactic polymers (Stereochemistry)
Fig. Atactic, isotactic and syndiotactic polymers.
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16. Fig. Homopolymers and Copolymers

19. Organic and Inorganic Polymers
A polymer whose backbone chain is essentially made up of carbon atoms is termed as an organic polymer. The atoms attached to side valencies are oxygen, nitrogen, hydrogen etc. Majority of synthetic polymers are organic polymers, for example PE, PVC.
On the other hand, the polymers that do not contain a carbon atom in their backbone chain are called inorganic polymers.

20. Elastomers, Fibers, Resins and Plastics
Elastomer: The polymers which undergo very long elongation when pulled apart, and return to their original length on release are called elastomers. Example Natural rubber, Buna-S, etc
Fibers: These are long, thin and thread like polymers, whose length is at least 100 times their diameter. They do not undergo stretching and deformation like elastomers. Example jute, wood, silk
Resins: These are low molecular weight polymers used as adhesives. They can be in the form of liquids or powder.. Example Urea-formaldehyde, epoxy resin.
Plastics: These are polymers, which can be molded into desired shapes by the application of heat and pressure. Example PVC, PC, Teflon

21. Structure–Property Relationship of Polymers
Strength: Melt viscosity, impact and tensil strength are few mechanical properties. Tensile strength and impact strength increase with molecular mass up to a certain point and then become constant. The melt viscosity of the polymer initially shows a gradual increase with the molecular mass and steep increase at higher molecular mass. Commercially a polymer should have high tensile strength and impact strength and low melt viscosity.
Crystallinity: Crystallinity depends on-
(1) structure - DC linearity and DC1/branching
(2) polar group – DC  polarity
(3) stereo regular arrangement- DC  stereoregularity
Degree of crystallinity of polymer depends on its structure. Linear polymer will have high crystallinity. Eg HDPE is more crystalline than LDPE. LDPE is more crystalline than Polystyrene. Isotactic, syndiotactic is highly crystalline than atactic styrene. Nylon 66 high degree of crystallinity. Polymers having polar groups can formed hydrogen bond with neighboring chain.

22. Elasticity: It is mainly because of uncoiling and recoiling of molecular chains on application of force. For a polymer to show elasticity, the individual chains should not break on prolonged stretching. Breaking take place when the chain slip past each other and get separated. Can be avoided by :
Introducing cross linking
Avoiding bulky side groups
more non-polar groups in chain

23. Plastic deformation: Thermoplastic material/ polymer on application of heat and pressure, initially become soft, flexible and undergo deformation. On further heating above their melting point (Tm) they melt and flow. Thermoplastic exhibit plastic deformation (linear chains , weak vander waals force).While thermosetting plastic doesn’t because of cross linking.
Chemical Resistivity: It depends on the structure of polymer and nature of attacking reagent. When the chemicals attack on polymer, it first softens, swells and loses its strength, and then dissolves. It also depends on several factors such as polar and non polar groups, molar mass, degree of crystallinity, cross linking etc. CR  Crystallinity, CR  CL
Non-elastic Nature of Fibers: The chain mobility is reduced by very close packing of the polymer chain backbone without cross linking. Polar groups and aromatic rings in the backbone chain impart high strength to the polymer fiber.

24. Glass transition temperature (Tg)
It is the temperature below which a polymer is hard, brittle and above which it is soft and flexible. Denoted by Tg. Hard brittle state is known as glassy state and soft flexible state is called the rubbery state.
Factors affecting Tg:
1. Flexibility: Presence of rigid groups (aromatic, bulky) in the carbon chain backbone hinders freedom of rotation. This restriction in the chain mobility increases the Tg value.
2. Effect of side group: Poly(-methyl styrene) has higher Tg (170 oC) while polystyrene has lower (100 oC) due to presence of extra methyl group which hinders free rotation.
3. Intermolecular forces: Presence of large number of polar groups in the molecular chain lead to strong intermolecular cohesive forces which restricts the segmental/ molecular mobility. This leads to increase in Tg value.

25. 4. Branching and Cross linking: A small amount of branching will reduce the value of Tg, because the free volume increases with branching and thus decreases the Tg. High density of branching brings the chain closer and thus reduces the mobility, thereby increasing Tg.
5. Presence of Plasticizers: Addition of plasticizers reduces the Tg value. Eg diisooctyl phthalate which is added to PVC reduces its Tg from 80 c to below room temperature.
6. Stereo-regularity: Tg increases with stereo-regularity. Thus Tg of isotactic polymer is greater than syndiotactic which in turn has greater tg than atactic polymer.
7. Molecular Weight: Tg of all polymers increases with molecular weight up to 20, 000 and beyong this the effect is negligible.

26. Significance of Tg Tg value is a measure of flexibility
Its value gives an idea of thermal expansion, heat capacity, refractive index, electrical and mechanical properties of a polymer.
Its value decides whether a polymer at room temperature will behave like rubber or plastic.
It helps in choosing the right temperature for fabrication.

27. Flexibility
Tg  1/DFR
+DFR + Linear and -DFR + Bulky group
Polythene (Tg= - 110oC), Polyethylene terephthalate (Tg= 69oC) and Polystyrene (Tg= 100oC)
Effect of side group
+DFR + linear and DFR + side group
-methyl styrene (Tg= 170oC) and polystyrene (Tg= 100oC)
Intermolecular force
Tg  IF
+IF + polar group (restrict segmental/molecular mobility
Polypropylene (Tg= -18oC) and Nylon- 6,6 (Tg= 57oC)
Branching and cross linking(CL)
Tg  branching(CL)
+CL – free volume
LDPE has lower Tg value than CL XLDPE
Presence of plasticizers
Tg  1/ plasticizers
Diisooctyl phthalate on addition to PVC reduces its Tg 80oC below room temperature
Stereo-regularity
Tg  stereo-regularity
Tg isotactic> syndiotactic> atactic
Molecular weight
Tg  MW
Increases with MW upto 20,000 and beyond this effect is negligible

28. Plastics Classification: Thermoplastic and Thermosetting
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29. Plastic Molding 1. Involves conversion of the solid polymer into desirable shape and size. 2. During molding the plastic material is heated to the appropriate temperature for it flow and material is shaped and then cooled to preserve the desired shape.

30. Methods of plastic molding
Injection molding
Extrusion molding
Blow molding
Injection blow molding
Thermoforming
Compression molding
Transfer molding
Injection-Compression molding
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31. Injection molding
Fig : Injection molding with (a) plunger, (b) reciprocating rotating screw, (c) a typical part made from an injection molding machine cavity, showing a number of parts made from one shot, note also mold features such as sprues, runners and gates.

32. Injection molding
Known quantity of polymer may in the form of granules , pellet or powder is fed to the hopper.
2. Passed to a hot chamber where the polymer material soften flows under the pressure applied by means of electrically operated plunger.
3. As the plunger moves in the forward direction ,the soften material passes into mold through a nozzle , solidifies upon cooling ,takes the shape of mold.

33. Advantages of Injection molding
speed production
Low costs in mass production
Very low loss of material
Flexibility to make parts with complex shapes
High Precision

34. Makings Bottles caps Mugs Dustbins Automotives dashboards Chairs
Applications
Makings
Bottles caps
Mugs
Dustbins
Automotives dashboards
Chairs

35. Extrusion Molding
Production of thermoplastic material into finished articles such as sheets, films and rod.
Done by using machine Extruders.
Raw materials in the form if thermoplastic pellets, granules, or powder, placed between the screw and extruder barrel.(feed zone)
The barrel is equipped with a screw . As screw rotates , the pellets are dragged forward and compressed (transition or compaction zone)
Heaters around the extruder’s barrels heats the pellets and liquefies them. (molten plastic) (metering zone).
Screw has 3-sections
Feed section
Melt or transition section
Pumping section.

36. Extruders

37. The screw depth is constant in both the feed and metering zones and varies in transition zone to begin generating pressure and to force the pellets to begin to melt.
Length of each zone in screws design varies according to type of plastic being processed. Example LDPE- melt gradually ,the overall length of the screw is roughly divided into three zone.
Nylon- have sharp melting point ,screw designed such that transition zone only consist of one turn of the screw flight.
PVC – Prone to thermal degradation and melt very gradually may be processed with screw whose entire length is composed of a compression zone.

38. Low initial setup Fast setup Low production cost
Advantages
Low initial setup
Fast setup
Low production cost

39. Application Manufacture Tubes Rods Plumbing pipes Electric cable
e) Door insulation seals
f) optical fibres

40. Compression Molding
Fig : Types of compression molding, a process similar to forging; (a) positive, (b) semi positive, (c) flash (d) Die design for making compression-molded part with undercuts.

41. Compression Molding Thermoplastic are molded by this method.
Known quantity of polymer (resin) which may in any form (powder or pellet) is placed in the lower portion of mold cavity.
It is heated electrically or by passing steam to soften the material.
The mold cavity gets filled with fluidized plastic.
The melt is compressed by the upper mold.
compression mass gets cured and hardened and is open after cooling and the article removed.

42. Advantages and Applications
Low cost
Very low loss of materials
God surface finish
Fast setup time
Electrical parts
Cooker Handles
Electronic devices
Appliance housing and large container.

43. Elastomers (Rubber) Vulcanization
Natural rubber is prepared from latex of Hevea rubber trees or gutta-percha and balata. It is a linear polymer of isoprene and is called polyisoprene.
Vulcanization
The physical properties of rubber can be altered by vulcanization.
Vulcanization is the cross-linking of polymer chains with sulfur atoms by applying heat.
Vulcanization increases the abrasion resistance and the useful temperature range of rubber.
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44. A Segment of Vulcanized Rubber
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45. The double bonds in isoprene polymer allows for cis-trans isomers.
Cis-trans isomers are molecules that differ only in the spatial orientation of their atoms
Natural rubber is cis-polyisoprene.
Gutta-percha is trans-polyisoprene
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47. Properties of Vulcanized rubber
Good tensile strength
Excellent resilience.
Low water absorption capacity
Higher resistance to oxidation.
Resist organic solvents as petrol, benzene, carbon tetrachloride.
Good electrical insulator.
Wide useful range -40 to 100 oC.
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48. Composites
Modern technology require such as aircraft application –low density, high strength, good corrosion resistance, good abrasion and impact resistance .
Not possible by single use of any metal, alloys, creamic.
Search of particle leads to composite.
Two different materials combine to form a material suitable for structure application as refer as composites.
A composite is a combined material formed by the assembly of two or more components, such as fillers or reinforcing agents and a compatible matrix binder in order to obtain specific characteristic properties.
Made up of two phases- matrix (continuous part or binder of composite materials and dispersed phase constructed by reinforcing particulates and fillers.
Classification:
Matrix constituent: OMCs, MMCs, CMCs
Reinforcement form: Fiber reinforced composites, laminar composites, particulate composites
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49. -Components of a composite do not dissolve or merge completely into each other but act together while retaining their individual properties.
Matrix constituent: OMCs (Organic matrix composites), MMCs (metal matrix composites), CMCs( ceramics matrix composites)
Term organic matrix composites include –polymer matrix composites and carbon matrix composites.(Carbon-carbon composites)
-Second classification – refer to reinforcement form,

50. Laminar Composites
-Long with sandwich structure belong to the class of structural composites.
Composed of thin layers held together by matrix.
Sheets or panels of constituting materials are stacked and glued together with different orientation that yield material with high isotropic strength.
Materials used in fabrication- include sheets, papers, glass fibers are embedded in plastic matrix.

52. Conducting polymers Before 1960 organic polymers used as insulators.
In 1960 Chemist Shirakawa ,Plastic research lab. BASF, Germany, accidentally added a catalyst 1000 times more than the required during polymerization of acetylene ,which result in conducting polyacetylene.
Organic polymers having electrical conductance of the order of conductors are called conducting polymers.
Classification:
Extrinsically conducting polymers (conductivity due to mixing conducting fillers like metal fibers, metaloxide, carbon black with insulating materials)
Also called as Conductive element filled polymers.
Insulation material formed the continuous phase and the added filler form the conducting networks.
Minimum concentration of conducting filler has to be added so that polymers start conducting.
Conductance is not due to matrix is due to fillers.

53. Intrinsically conducting polymers (for example, poly (p- phenylene), polyacetylene, polyaniline)
-Conductivity is due to organic polymers themselves.
They conduct electricity when doped with Oxidizing ,reducing agents or protonic acids

54. Conducting polymers with conjugated pi- electrons
-due to high delocalized Pi- electron systems organic polymer has conductance in the range of conductor are called as inherently or intrinsically conducting polymers or synthetic metals.
EX-
1. Poly (p- phenylene)
2. polyaniline
3. polyacetylene
These conjugated polymers in their pure state are insulators or semiconductor. (pi- electron are localized)
These electron are delocalize on doping and conduct electricity..
Dopant are oxidizing (p-doping) , reducing( n-doping), protonic acid (H-doping)
Redox doping of organic conductor s is similar to doping of silicon semiconductor.

55. Polyacetylene
Consists of large numbers of carbon atom linked by alternating single and double bond.
Conductivity of pure polyacetylene is 4.4x10 -5 S/cm. Upon doping with oxidizing agent like iodine , the conductivity increases to 400 s/cm.
Oxidative dopant iodine takes an electron from the Pi- backbone of the polyacetylene chain and create a positive centre (hole) on one of the carbon. The pi- electron resides on the other carbon making it a radical. The radical ion is known as Polaron.
Dipolaron (soliton) is formed is formed on further oxidation. These radicals migrate and combine to establish a backbone double bond.
Two electron removed ,chain have two(+ve) holes. The chain as whole neutral but holes are mobile. When potential is applied these holes migrates from one carbon to other and account for conductivity.

56. Discuss in terms of VB and CB
When Pi- bond is formed VB( Valence band) and CB (conduction band) are created.
Before doping sufficient gap between in VB and CB. Electron remains in VB.
Upon doping Polaron and solitons are formed which results in formation of new localized electronic states that fills the energy gap between VB and CB.
Sufficient solitons are formed , a new mid gap band formed which overlaps the CB and VB allowing the electron to follow.

57. Polyaniline
Phenylene based polymer having flexible –NH-group flanked on either side by a phenyl ring.
Physicochemical properties are due to –NH- group.
Exists in variety of forms (oxidation states) that differ in conductivity.
Most common green protonated emeraldine salt has conductivity in the order of semiconductor 1 S/cm. its higher than ordinary polymer but lower than conductor.
Emeraldine form of polyaniline can also be electrochemically oxidized or reduced in aqueous acid resulting in Pernigranline (PS). And Leuco-emeraldine (LS) salts. This process is known as acid doping.
Redox reactions occur with the motion of electron and proton in pH3.0

58. Application Used as antistatic materials
used as electrode materials for rechargeable batteries
used in light emitting didodes
Used in display devices
Used as conductive track on printed circuit boards
Used as resistor for lithography
Used in information storage devices
Used as humidity sensor devices , gas sensors, radiation sensors.
Used in electrochromic display window
Used in fuel cell as electrocatalytic materials.
Used as membrane for gas separation .

59. Some Important Commercial Thermoplastics
Polythylene (PE): LDPE and HDPE
Polypropylene
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60. Polystyrene Polyvinylchloride Engineering Chemistry
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61. Polytetrafluoroethylene/Teflon
Polyvinyl Acetate
Polytetrafluoroethylene/Teflon
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62. Polystyrene Engineering Chemistry
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63. Polymethyl Methacrylate/Plexiglass
Polyurethanes
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64. Some Important Commercial Thermosetting Resins
Phenol–Formaldehyde Resins
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65. Both resol and novolac on curing with wood flour filler give highly cross-linked product called Bakelite.
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66. Amino Resins Urea–Formaldehyde Resin Engineering Chemistry
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