Unit 3

• Polymer


  A molecule, made from joining together many small molecules called monomers
• Polymerization


  The process where constituent elements called monomers are reacted together to form polymer chains
• Types of polymers based on origin

  • Natural polymers
  • Synthetic polymers
• Natural polymers


  • Occur naturally and are found in plants and animals (e.g. proteins, starch, cellulose, rubber)
  • Include biodegradable polymers called biopolymers
• Synthetic polymers


  • Man-made polymers (e.g. plastic, nylon-6,6, polyethers)
• Types of polymers based on chemical structure


  • Homopolymer
  • Copolymer
• Homopolymer


  Polymer which consists of one type of monomer
• Copolymer


  Polymer derived from more than one type of monomer
• Types of polymers based on polymeric structure

  • Linear polymers
  • Branched-chain polymers
  • Cross-linked polymers
• Linear polymers


  Polymers containing long and straight chains
• Branched-chain polymers


  Polymers where linear chains form branches
• Cross-linked polymers


  Polymers composed of bifunctional and trifunctional monomers with stronger covalent bonds
• Types of polymers based on arrangement of monomers

  • Block polymer
  • Graft polymer
• Block polymer


  Polymer consisting of relatively long sequences of identical monomer units
• Graft polymer


  Branched polymer where the backbone is formed from one type of monomer and the branches are formed from another type of monomer
• Types of polymers based on tacticity

  • Isotactic polymer
  • Syndiotactic polymer
  • Atactic polymer
• Isotactic polymer


  Polymer where the side groups lie on the same side of the chain
• Syndiotactic polymer


  Polymer where the side groups are arranged in an alternate manner
• Atactic polymer


  Polymer where the side groups are arranged in an irregular or random manner
• Types of polymers based on thermal behavior

  • Thermoplastics
  • Thermosets
• Thermoplastics


  Polymers which are easily softened upon heating
• Thermosets


  Polymers which change irreversibly into hard and rigid materials on heating and cannot be reshaped
• Types of polymers based on molecular forces

  • Elastomers
  • Fibers
• Elastomers


  Polymers which can be easily stretched by applying small stress
• Fibers


  Polymers which have strong intermolecular forces between the polymer chains
• Types of polymers based on modes of synthesis

  • Addition polymers
  • Condensation polymers
• Addition polymers


  Polymers formed when the same monomers are added, usually alkenes
• Condensation polymers


  Polymers formed when two monomers react with the elimination of a smaller molecule
• Sources of natural polymers

  • Plants (cellulose, starch, rubber)
  • Animals (DNA, proteins, silk)
• Other natural polymers include lignin and chitin
• Synthetic polymers are mostly derived from natural polymers
• Essential amino acids


  • Methionine
  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine
• Silk is a kind of protein produced by silkworms to make their cocoon, and it is used for the production of silk cloth
• Lignin


  A polymer found in trees, together with cellulose, makes trees rigid
• Chitin


  A polymer which composes the exoskeleton of crustaceans such as crabs and shrimps, and is also found in the cell wall of fungi like mushrooms
• Synthetic polymers


  Mostly derived from petroleum/crude oil, and manufactured in factories. Synthetic polymers include fibers, elastomers, and the most commonly encountered are PLASTICS
• Plastics


  Comes from the Greek word "plastikos", which means "to grow or form"
• 7 Types of Plastics

  • Polyethylene Terephthalate (PET or PETE)
  • High-Density Polyethylene (HDPE)
  • Polyvinyl Chloride (PVC)
  • Low-Density Polyethylene (LDPE)
  • Polypropylene (PP)
  • Polystyrene (PS)
  • Other (e.g. Polycarbonate (PC), and other plastics not included in 1-6)
• Polyvinyl Acetate (PVA)


  Used in regular glue
• Ethylcyanoacrylic


  Used in superglue (stronger than PVA)