Polymers - Classification of polymers

  • Based on sources "
  • Synthetic polymers
    • Plastics
      • Thermoplastics
        • Examples: polyethylene, polypropylene
        • Structure: linear or branched polymer chains
        • Properties: can be molded and remolded upon heating
      • Thermosetting plastics
        • Examples: melamine formaldehyde, epoxy resins
        • Structure: cross-linked polymer chains
        • Properties: become hard and rigid upon heating and cannot be remolded
    • Fibres
      • Examples: polyester, nylon
      • Structure: long chains with high tensile strength
      • Properties: strong, resistant to stretching and have high melting points "
  • Natural polymers
    • Proteins
      • Examples: collagen, insulin
      • Structure: amino acid chains folded into specific shapes
      • Properties: essential for the structure and function of living organisms
    • Polysaccharides
      • Examples: cellulose, starch
      • Structure: long chains of sugar molecules
      • Properties: provide structural support in plants and serve as energy storage in animals
    • Nucleic acids
      • Examples: DNA, RNA
      • Structure: nucleotide chains containing genetic information
      • Properties: involved in genetic coding and protein synthesis "
  • Semi-synthetic polymers
    • Cellulose acetate
      • Example: cellulose acetate film
      • Structure: cellulose modified with acetic acid
      • Properties: used for photography film and cigarette filters
    • Rayon
      • Example: viscose rayon
      • Structure: natural cellulose chemically treated
      • Properties: used in textile industry for clothing "
  • Commercial polymers
    • Rubbers
      • Examples: natural rubber, synthetic rubber
      • Structure: long polymer chains with elastic properties
      • Properties: used in tires, belts, and other flexible materials
    • Adhesives
      • Examples: epoxy, polyvinyl acetate
      • Structure: polymers with sticky properties
      • Properties: used for bonding materials together
    • Coatings
      • Examples: polyurethane, epoxy
      • Structure: polymers that form a protective layer on surfaces
      • Properties: used for protection and decoration " Slide 11

Polymers - Classification of polymers

  • Based on structure "
  • Linear polymers
    • Examples: polyethylene, polypropylene
    • Structure: long chains of polymer units connected end-to-end
    • Properties: flexible and have low density
    • Application: plastic bags, packaging materials
  • Branched polymers
    • Examples: LDPE (low-density polyethylene)
    • Structure: long chains with branched side chains
    • Properties: more compact and have higher density compared to linear polymers
    • Application: food packaging, toys
  • Cross-linked polymers
    • Examples: vulcanized rubber, epoxy resins
    • Structure: polymer chains linked together with covalent bonds
    • Properties: rigid and have high strength
    • Application: tires, electrical insulations
  • Network polymers
    • Examples: bakelite, melamine-formaldehyde
    • Structure: three-dimensional network of polymer chains
    • Properties: hard and rigid
    • Application: electrical switches, kitchenware " Slide 12

Polymerization - Addition Polymerization

  • Steps involved "
  • Initiation
    • Initiation of the reaction by a free radical, cation, or anion
    • Examples: Benzoyl peroxide, UV light
    • Reaction: Formation of an active species and initiation of polymer chain growth
  • Propagation
    • Addition of monomer units to the active species
    • Reaction: Repeated addition of monomers to the growing polymer chain
  • Termination
    • Termination of the reaction either by the reaction of two active species or by a suitable terminating agent
    • Reaction: Inhibition of radical/cation/anion to form stable molecules
  • Examples
    • Formation of polyethylene from ethylene monomer
    • Formation of polypropylene from propylene monomer
  • Advantages
    • High yield of polymer
    • Ability to control the molecular weight of the polymer
    • Wide range of monomers can be used " Slide 13

Polymerization - Condensation Polymerization

  • Steps involved "
  • Formation of reactive groups
    • Formation of reactive groups in monomers (usually functional groups like -OH, -COOH, -NH2)
    • Examples: Dicarboxylic acid, diol
  • Condensation reaction
    • Formation of small molecules (usually water or another simple compound) during the polymerization process
    • Reaction: Joining of reactive groups with the elimination of small molecules
  • Polymer chain growth
    • Repeated condensation reactions between monomer units
    • Reaction: Growth of the polymer chain and elimination of small molecules
  • Examples
    • Formation of Nylon 6,6 from adipic acid and hexamethylene diamine
    • Formation of Polyester from terephthalic acid and ethylene glycol
  • Advantages
    • Flexibility in choosing monomers
    • Production of water as a byproduct can be useful " Slide 14

Polymerization - Addition vs Condensation Polymerization

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  • Addition polymerization
    • Monomers involved: Unsaturated compounds
    • Type of reaction: Addition of monomers to a growing chain
    • Byproduct: None
    • Examples: Polyethylene, polystyrene
  • Condensation polymerization
    • Monomers involved: Compounds with reactive groups
    • Type of reaction: Formation of a polymer by the elimination of small molecules
    • Byproduct: Water, alcohol, etc.
    • Examples: Nylon, Polyester
  • Differences
    • Addition polymerization: No byproducts, controlled molecular weight
    • Condensation polymerization: Byproducts formed, ability to use a wide range of monomers
  • Application
    • Addition polymerization: Plastics, packaging materials
    • Condensation polymerization: Fibers, clothing materials " Slide 15

Polyethylene - Properties and Applications

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  • Types of polyethylene
    • Low-density polyethylene (LDPE)
      • Properties: Flexible, transparent, resistant to chemicals
      • Applications: Plastic bags, squeeze bottles, food packaging
    • High-density polyethylene (HDPE)
      • Properties: Strong, stiff, resistant to chemicals
      • Applications: Pipes, fuel tanks, detergent bottles
    • Linear low-density polyethylene (LLDPE)
      • Properties: Flexible, highly resistant to impact
      • Applications: Stretch films, trash bags
  • Structure
    • Linear or branched chains of ethylene monomer units
    • Polymerization: Addition polymerization
  • Properties
    • Low density, high strength, good electrical insulation
    • Melting point: 110-130 °C
  • Processing
    • Extrusion, injection molding, blow molding " Slide 16

Polystyrene - Properties and Applications

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  • Structure
    • Linear chains of styrene monomer units connected by covalent bonds
    • Polymerization: Addition polymerization
  • Properties
    • Hard, rigid, brittle
    • Transparent, good electrical insulation
    • Melting point: 240-260 °C
  • Applications
    • Packaging materials, insulation boards
    • Disposable coffee cups, food containers
    • CD cases, toys
  • Processing
    • Injection molding, extrusion
  • Environmental impact
    • Non-biodegradable, resistance to degradation " Slide 17

Nylon - Properties and Applications

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  • Types of nylon
    • Nylon 6
      • Properties: High melting point, flexibility, good tensile strength
      • Applications: Carpets, fabrics, ropes
    • Nylon 6,6
      • Properties: High melting point, excellent tensile strength, stiffness
      • Applications: Clothing, luggage, automotive parts
  • Structure
    • Condensation polymerization of adipic acid and hexamethylene diamine
    • Amide groups in the polymer chain
  • Properties
    • Good strength, resistance to wear and abrasion
    • Melting point: 200-220 °C
  • Processing
    • Melt spinning, injection molding " Slide 18

Polyester - Properties and Applications

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  • Types of polyester
    • Polyethylene terephthalate (PET)
      • Properties: High strength, good dimensional stability, transparency
      • Applications: Clothing, beverage bottles, packaging films
    • Polybutylene terephthalate (PBT)
      • Properties: Excellent resistance to heat and chemicals, good electrical insulation
      • Applications: Automotive parts, electrical connectors
  • Structure
    • Condensation polymerization of terephthalic acid and ethylene glycol
    • Ester groups in the polymer chain
  • Properties
    • High tensile strength, low moisture absorption
    • Melting point: 250-260 °C
  • Processing
    • Melt spinning, injection molding " Slide 19

Plastics - Advantages and Disadvantages

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  • Advantages
    • Versatility: Can be molded into different shapes and sizes
    • Durability: Long-lasting and resistant to wear and tear
    • Light weight: Easy to handle and transport
    • Cost-effective: Relatively inexpensive compared to other materials
    • Wide range of properties: Can be designed for specific applications
  • Disadvantages
    • Environmental impact: Non-biodegradable, can contribute to pollution
    • Recycling challenges: Difficult to recycle due to different types of plastics
    • Health concerns: Some plastics may release harmful chemicals

Slide 21

Atomic Structure - Electrons in Atoms

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  • Electromagnetic spectrum
    • Range of all possible electromagnetic radiation
    • Includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays
  • Dual nature of electrons
    • Electrons exhibit both particle and wave-like properties
    • Wave-particle duality: the behavior of electrons is described by both particle and wave equations
  • Quantum mechanics
    • Study of particles at the atomic and subatomic level
    • Describes the behavior of electrons using wave functions
  • Atomic orbitals
    • Regions in space where electrons are likely to be found
    • Represented by electron probability density plots
  • Quantum numbers
    • Describe the energy level, shape, and orientation of atomic orbitals
    • Principal quantum number (n), azimuthal quantum number (l), magnetic quantum number (m), spin quantum number (s)
  • Electron configuration
    • Distribution of electrons in different atomic orbitals
    • Follows the Aufbau principle, Pauli exclusion principle, and Hund’s rule

Slide 22

Periodic Table - Trends and Properties

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  • Periodic table organization
    • Elements arranged in order of increasing atomic number
    • Periods: Horizontal rows
    • Groups: Vertical columns
  • Periodic trends
    • Atomic radius: decreases from left to right across a period, increases down a group
    • Ionization energy: increases from left to right across a period, decreases down a group
    • Electronegativity: increases from left to right across a period, decreases down a group
  • Alkali metals
    • Group 1 elements (except hydrogen)
    • Very reactive, low ionization energies
    • Examples: lithium (Li), sodium (Na), potassium (K)
  • Halogens
    • Group 17 elements
    • Highly reactive nonmetals, high electronegativities
    • Examples: fluorine (F), chlorine (Cl), bromine (Br)
  • Noble gases
    • Group 18 elements
    • Stable, nonreactive, full outer electron shells
    • Examples: helium (He), neon (Ne), argon (Ar)

Slide 23

Chemical Bonding - Ionic Bonding

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  • Ionic bonding
    • Bond formation between metals and nonmetals
    • Transfer of electrons from one atom to another
    • Formation of cations (positive ions) and anions (negative ions)
  • Electron transfer
    • Metals donate electrons to nonmetals to achieve a stable electron configuration
    • Ionic compounds composed of cations and anions held together by electrostatic forces
  • Properties of ionic compounds
    • High melting and boiling points
    • Crystalline structures
    • Good electrical conductivity when dissolved in water or molten
  • Examples
    • Sodium chloride (NaCl): Na+ and Cl- ions
    • Calcium oxide (CaO): Ca2+ and O2- ions

Slide 24

Chemical Bonding - Covalent Bonding

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  • Covalent bonding
    • Bond formation between nonmetals
    • Sharing of electron pairs between atoms
  • Electron sharing
    • Valence electrons are shared to achieve a stable electron configuration
    • Formation of molecules
  • Types of covalent bonds
    • Single bond: sharing of one electron pair
    • Double bond: sharing of two electron pairs
    • Triple bond: sharing of three electron pairs
  • Molecular structures
    • Lewis structures: show the arrangement of atoms and valence electrons in a molecule
    • VSEPR theory: predicts the shape of molecules based on the repulsion between electron pairs
  • Examples
    • Methane (CH4): single covalent bonds
    • Oxygen molecule (O2): double covalent bond

Slide 25

Chemical Bonding - Polar Covalent Bonding

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  • Polar covalent bonding
    • Intermediate between ionic and covalent bonding
    • Unequal sharing of electrons between atoms
  • Electronegativity difference
    • Determines the polarity of a bond
    • Electron density shifted towards the more electronegative atom
  • Dipole moment
    • Measure of the separation of positive and negative charges in a molecule
  • Polar molecules
    • Have a net dipole moment due to the presence of polar bonds
    • Examples: water (H2O), ammonia (NH3)
  • Nonpolar molecules
    • Have no net dipole moment
    • Examples: methane (CH4), carbon dioxide (CO2)

Slide 26

Chemical Reactions - Types of Chemical Reactions

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  • Combination reaction
    • Two or more substances combine to form a new substance
    • General equation: A + B -> AB
    • Example: 2H2 + O2 -> 2H2O
  • Decomposition reaction
    • A single substance breaks down into two or more simpler substances
    • General equation: AB -> A + B
    • Example: 2H2O -> 2H2 + O2
  • Displacement reaction
    • An element from one compound is replaced by another element
    • General equation: A + BC -> AC + B
    • Example: Zn + 2HCl -> ZnCl2 + H2
  • Redox reaction
    • Involves the transfer of electrons between reactants
    • Oxidation: loss of electrons, reduction: gain of electrons
    • Example: 2Na + Cl2 -> 2NaCl

Slide 27

Chemical Reactions - Balancing Chemical Equations

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  • Balancing chemical equations
    • Ensures that the number of atoms of each element is the same on both sides of the equation
  • Step 1: Count atoms
    • Count the number of each type of atom on both sides of the equation
  • Step 2: Add coefficients
    • Adjust the coefficients in front of the formulas to balance the equation
  • Step 3: Verify
    • Check that the number of atoms is balanced for each element
  • Tips
    • Start by balancing elements that appear in only one reactant and product
    • Use the lowest whole number coefficients
  • Example: Balancing the equation for the combustion of methane
    • CH4 + O2 -> CO2 + H2O

Slide 28

Chemical Equilibrium - Le Chatelier’s Principle

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  • Chemical equilibrium
    • Dynamic state where the rate of the forward and reverse reactions are equal
    • Concentrations of reactants and products remain constant
  • Le Chatelier’s principle
    • When a system at equilibrium is disturbed, it will respond to minimize the disturbance
  • Factors affecting equilibrium
    • Concentration: increasing reactant or product concentration shifts the equilibrium
    • Pressure: increasing pressure favors the reaction with fewer moles of gas
    • Temperature: increasing temperature favors the endothermic reaction or the reaction with higher energy
  • Examples
    • Equilibrium shift due to concentration change: N2(g) + 3H2(g) <-> 2NH3(g)
    • Equilibrium shift due to temperature change: 2SO2(g) + O2(g) <-> 2SO3(g)

Slide 29

Acids and Bases - Arrhenius Concept

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  • Acids
    • Release hydrogen ions (H+) in aqueous solution
    • Examples: hydrochloric acid (HCl), sulfuric acid (H2SO4)
  • Bases
    • Release hydroxide ions (OH-) in aqueous solution
    • Examples: sodium hydroxide (NaOH), potassium hydroxide (KOH)
  • Arrhenius concept
    • Acid: substance that increases the concentration of H+ ions in solution
    • Base: substance that increases the concentration of OH- ions in solution
  • Neutralization reactions
    • Acid + base -> salt + water
  • pH scale
    • Measures the acidity or alkalinity of a solution
    • Ranges from