polymers ppt revised 2023.pdf applied chemistry

Polymers: An In-Depth Study

Introduction to Polymers

Polymers are large molecules composed of repeating structural units called monomers. These macromolecules are essential in various applications, ranging from everyday household products to advanced industrial uses. Their unique properties make them indispensable in fields such as medicine, engineering, and environmental sciences.

Classification of Polymers

Polymers can be classified based on different criteria:

1. Based on Source of Origin

Natural Polymers: These are found in nature and include proteins (such as silk and collagen), nucleic acids (DNA and RNA), and polysaccharides (cellulose and starch).

Synthetic Polymers: Man-made polymers include plastics (like polyethylene and polystyrene) and synthetic fibers (such as nylon and polyester).

Semi-Synthetic Polymers: Derived from natural polymers but chemically modified, such as rayon (modified cellulose) and cellulose acetate.

2. Based on Polymerization Process

Addition Polymers: Formed by the repeated addition of monomers without losing any small molecules. Examples include polyethylene and polypropylene.

Condensation Polymers: Formed by the loss of small molecules like water or methanol during polymerization. Examples include nylon and polyester.

3. Based on Molecular Structure

Linear Polymers: Consist of long, straight chains, e.g., high-density polyethylene (HDPE).

Branched Polymers: Contain side chains branching off the main chain, e.g., low-density polyethylene (LDPE).

Cross-Linked Polymers: Have interconnected chains providing rigidity, e.g., vulcanized rubber and Bakelite.

4. Based on Physical Properties

Thermoplastics: Soften upon heating and harden upon cooling. Examples include polyvinyl chloride (PVC) and polystyrene.

Thermosetting Polymers: Harden permanently after heating, such as epoxy resins and Bakelite.

Properties of Polymers

Polymers exhibit a wide range of physical, chemical, and mechanical properties, including:

Flexibility and Elasticity: Natural rubber and synthetic elastomers exhibit high flexibility.

Strength and Durability: Some polymers, like Kevlar, exhibit high tensile strength.

Lightweight Nature: Compared to metals, polymers are lightweight yet strong.

Chemical Resistance: Many polymers resist acids, bases, and solvents.

Thermal Insulation: Polymers like polystyrene act as excellent thermal insulators.

Polymerization Techniques

The synthesis of polymers involves different techniques, such as:

Bulk Polymerization: Monomers react in bulk without any solvents.

Solution Polymerization: Monomers dissolve in a solvent before polymerization.

Emulsion Polymerization: Uses water as the dispersion medium.

Suspension Polymerization: Monomers are suspended in a liquid medium with stabilizers.

Applications of Polymers

Polymers are crucial in various industries:

1. Packaging Industry

Used in plastic bags, containers, and films due to their lightweight and moisture-resistant properties.

Comm

3. FUNCTIONALITY OF A POLYMER

4. CLASSIFICATION OF POLYMERS

6. Addition Polymerisation
The monomers involved in these reactions
must be unsaturated

7. Condensation Polymerisation
Linking of every two monomer molecules will
result in a simple molecule such as HCl,
ammonia, water, etc., as a by-product.

11. Techniques to determine Molecular Weight of polymers
•Gel permeation chromatography
•Osmometry
•Light scattering
•Viscometry
•Cryoscopy
•Ebulliometry,
•Ultracentrifugation,
•Mass spectrometry
•End-group analysis.

12. Number average molecular
weight

13. Weight average molecular weight

14. In a polymer sample ,
35% of molecules have molecular mass 25000 g/mole,
35% of molecules have molecular mass 20000 g/mole,
Remaining molecules have mol mass 10000 g/mole
Calculate the number average and weight average molecular
mass

15. Polydispersion Index
Chain size distribution
Heterogeneity index

16. Polymers

17. POLYMERS CAN HAVE BOTH TRANSITION
TEMPERATURE AND MELTING TEMPERATURE

18. Tg depends on the mobility of the polymer chain

21. FACTORS AFFECTING T
g
▪Flexibility
▪Intermolecular forces
▪Molecular mass
▪Stereoregularity

22. Flexibility
C-C, C-O and C-N have high degree of freedom
More flexibility and low Tg
Aromatic & cyclic structures in side chain
More rigidity and high Tg
Polyphenylene
Polybutadiene
Tg = -110ºC
Tg = -85ºC
Tg = -83ºC

23. Branching & crosslinking
Tg = -110 Tg = 20 Tg = 100

24. Intermolecular forces
Strong polar attraction between molecules helps crystallization and hence higher Tg.
Tg = 50°CTg = -110

25. Tg = -110
Bakelite
Tg = 97°C

26. Molecular mass

27. Stereoregularity (Tacticity)
Polymers with chiral centres show different arrangements of atoms around them
Ex – Attactic Polypropylene – Gummy solid (useless)
Isotactic Polypropylene – Crystalline & Tough

28. Structure Property relationship
Tensile strength – High Crystallinity, higher tensile strength
High Crystallinity, high impact resistance
High stereoregularity leads to High Crystallinity
Ex- Isotactic – High Density Polyethylene-Crystalline
Syndiotactic – Polypropene, Polyvinylchloride- High crystalline
Atactic – Polypropene, Polyvinylchloride- Low crystalline
Chemical resistance – Depends on
•Unsaturation - Degradative oxidation Ex- Natural & Synthetic rubber
•Polar groups- Ester group (hydrolysis) Ex- Polyamide containing Nylon
•Molar mass – Heavy polymers are highly resistant

29. PLASTICS
Mouldable macromolecules with moderate intermolecular forces

33. COMPOUNDING OF PLASTICS
ADDITIVIES
•Resins
•Plasticizers
•Fillers
•Stabilizers
•Catalysts
•Pigments

34. Polymethylmethacrylate

35. Urea Formaldehyde Resin

36. Elastomers
Polymers with high molecular weight possessing
elasticity , exhibiting combination of local mobility
and overall rigidity which returns to its initial
dimension after deforming force is removed

37. Raw or Natural rubber or Poly isoprene
•Low heat resistance
•Chemical resistance
•Low elastic limit
•Requires vulcanization

38. BUTYL RUBBER
Properties
•Resistive to aging
•Low gas permeability
•Solvent resistant
•Heat resistant
•Electrical resistance

39. NITRILE RUBBER (BUNA-S)
Properties
High tensile strength
Resistant to heat,
Resistant to acids & bases
Resistant to solvents

40. Adhesives
Substance that is capable of holding materials together
in a functional manner by surface attachment that
resists separation.
Or
Substance that binds together two or more similar or
dissimilar materials so that resulting material can act or
be used as a single piece.
Ex- Epoxies, polyurethanes,cyanoacrylates, polyimides, silicones,
acrylics, polyamides,cyanoacrylates, polyacrylates.
Transitional zone arises in the interface between adherent and
adhesive and the exothermic reaction supplies energy for
developing bonds.

41. Epoxy resin:
Condensation of epichlorohydrine with bis - phenol-A at
60
o
Cin the presence of aqueous NaOH.

42. Applications
•Epoxy resins are mainly used as surface-coating
materials, which give outstanding toughness
flexibility, adhesion and chemical resistance.
•It can be used in both moulding and laminating
techniques to prepare glass fiber-reinforced
articles with good mechanical strength, chemical
resistance and electrical insulating properties.
•It is used as skid resistant for highway surfacing.
•To impart crease-resistance and shrinkage control
on cotton and rayon fabrics.
•It is used as stabilizers for vinyl resins.

43. Polymer composites
Two or more distinct components, which combine to
form a new class of materials, suitable for structural
applications, are referred as composite materials.

44. Made of two components namely
(i) Matrix (ii) Fiber
Matrix - Continuous phase surrounding the fiber dispersed phase, helps
in retaining the composite mass, shape and binds the fiber together but
retaining its entity. Ex- epoxy resin, polyamide.
Fibers - molecules with long chain length and few microns diameter. The
strength and stiffness of fibers decides the strength and stiffness of the
composites. Ex- glass, carbon fiber, Kevlar.

45. Classification

47. Properties of composites
1. High strength to weight ratio
2. High flexibility and toughness
3. Fire retarding and fire resisting properties
4. Good insulating properties and chemical resistance
5. Low thermal conductivity
6. Highly ductile and malleable
Application of composites
1. Used in making laminates and electronic gadgets
2. Used in making Chimney duct, chemical storage tanks and boat hulls
3. Manufacturing of containers used for micro waves and form insert
4. Used in making fiberglass
5. Used in acoustical insulation

48. Kevlar (fibre)
Prepared by poly-condensation reaction between
aromatic dichloride and aromatic diamines.
Properties: Kevlar is exceptionally stronger; it has high heat stability and flexibility
Applications: It is used extensively in the aerospace and air craft industries. It is also
used for making tires, industrial belts, bullet proof vests, high strength cloths, car parts
(such as tyres, brakes, clutch lining) etc.

49. Carbon fibre
•5to 10 micrometers (0.00020–0.00039in) in
diameter
•composed mostly ofcarbonatoms.

52. Conducting Polymers
Polymers exhibiting electrical conductivity either
intrinsically due to extended conjugation or
extrinsically due to externally added dopants

53. P-type and n-type doping

54. Polyacetylene
First conducting polymer
Rigid, rod-like polymer
Alternating single and double bonds between the carbon atoms.

Conductivity σ is proportionate to number of charge carriers ‘n’ and their mobility ‘μ’
σ = n e μ

55. Bonding
Synthesis

56. Mechanism of Conduction
Oxidation with halogen (p-doping)

57. Reduction with alkali metal (n doping)

58. APPLICATIONS
•Electrostatic materials
•Antistatic clothing
•Electromagnetic shielding materials
•Conducting adhesives
•Electrolytes in printed circuit board
•Artificial nerves
•Thermal sensors
•Aircraft structures
•Electric displays

59. Polycarbonates
OR

60. Biodegradable polymers
Polymerthat breaks down after its intended purpose
by bacterial decomposition process to result in natural
byproducts such as gases (CO
2, N
2), water and inorganic
salts when exposed to microorganisms, aerobic, and
anaerobic processes.
The Carbon-Carbon either single or double bond is present which is not easily degradable
for ex POLYETHELENE

64. •These are the polymers liable to be broken
into small segments by enzymes produced by
microorganisms. In biodegradable polymers,
bonds that can be broken by enzymes are
inserted into the polymeric chain. Hence,
when buried as waste, the enzymes in the soil
can degrade the polymer.
•Generally, synthetic and biologically derived
polymers which degrade hydrolytically or
enzymatically through structural modifications
are termed as “Biodegradable polymers”.

65. STRUCTURAL REQUIREMENT TO BE BIODEGRADABLE
Main chain contains consist ofester,amide, andetherfunctional groups-OH group

66. CLASSIFICATION

67. CLASSIFICATION

68. Synthesis of Poly-glycolic acid