Polymerization

• Polymers


  The process of combining small molecules known as "monomers" to form a large chain or network of molecules
• Monomers


  Simple, varying molecular-weight hydrocarbons with two or more binding sites that form covalent linkages with other monomer molecules to form macromolecules or polymers
• Polymerization


  1. Monomers react to form a bond by replacing other molecules and forming by-products (usually water)

  2. Polymers formed depend on the monomers

  3. If the monomer has only one reactive end group, linear polymers are obtained

  4. Monomers with more than two reactive groups form a three-dimensional network
• Examples of polymers and their monomers

  • Polyester, nylon, proteins, carbohydrates
• Classification of polymers


  • Natural polymers
  • Synthetic polymers
  • Semi-synthetic polymers
• Natural polymers


  • Occur in nature and exist in natural sources like plants and animals
• Examples of natural polymers

  • Proteins (plants and animals), cellulose and starch (found in plants), rubber (harvested from the latex of a tropical plant)
• Synthetic polymers


  • Commercially synthesized by industries for human necessities
• Examples of synthetic polymers

  • Polyethylene (plastic used in packaging), Nylon fibers (used in clothes, fishing nets, etc.)
• Semi-synthetic polymers


  • Obtained via modification of natural polymers artificially in the laboratory by chemical reactions
• Examples of semi-synthetic polymers

  • Vulcanized rubber (Sulphur is used in cross-bonding the polymer chains found in natural rubber), cellulose acetate (rayon)
• Classification of polymers based on structure

  • Linear polymers
  • Branched polymers
  • Crosslinked or networked polymers
• Linear polymers


  • Polymers similar in structure to a long straight chain with identical links connected to each other
  • High melting and boiling points
  • Closely/ tightly packed, hence higher density
• Example of linear polymer


  • PVC is used to make electric cables and pipes
• Branched polymers


  • Polymers with branched structure
  • Have polymer chains as side groups
  • Loosely packed, thus low density
  • Melting and boiling points are lower than linear polymers
• Examples of branched polymers

  • Starch, glycogen, low-density polyethylene (LDPE)
• Crosslinked or networked polymers

  • Monomers are linked together to form a three-dimensional network
  • The monomers contain covalent solid bonds as they are composed of bi-functional and tri-functional in nature
  • These polymers are brittle and hard
• Examples of crosslinked or networked polymers

  • Bakelite (used in electrical insulators), Melamine
• Addition polymerization


  1. Addition reaction occurs

  2. Repeating units form a linear or branch structure depending on the type of monomer

  3. There is no loss of atom or molecule during addition

  4. Four types: free radical polymerization, cationic polymerization, anionic vinyl polymerization, coordination polymerization
• Free radical polymerization


  Addition polymer forms by adding atoms with a free electron (free radicals) in its valence shells
• Cationic polymerization


  A cation is formed, causing a chain reaction, forming a long chain of repeating monomers
• Anionic vinyl polymerization


  Polymerization of vinyl polymers with a strong electronegative group to form a chain reaction
• Coordination polymerization


  A catalyst controls the free radical polymerization and produces a polymer with more density and strength
• Condensation polymers


  1. Monomers react to form a bond by replacing other molecules and forming by-products (usually water)

  2. Polymers formed depend on the monomers

  3. If the monomer has only one reactive end group, linear polymers are obtained

  4. Monomers with more than two reactive groups form a three-dimensional network
• Examples of condensation polymers include Polyester, nylon, proteins, and carbohydrates
• Polymer industry


  • Combines chemistry, materials science, and engineering to transform raw materials, such as petroleum and natural gas, into polymers, such as plastics, rubbers, and synthetic fibers
  • One of the largest global manufacturing sectors
  • Continuous innovation is a hallmark, enhancing the properties of existing polymers
  • The industry collaborates with multiple industries to tailor polymers to specific applications, ensuring materials meet exact performance and safety standards
• Types of Polymers used in Industry

  • Thermoplastics
  • Thermosetting plastics
  • Elastomers
• Thermoplastics


  Moldable upon heating and can be reshaped
• Examples of thermoplastics


  • Polyethene (PE) is used in packaging, polycarbonate (PC) is used for bulletproof glass
• Thermosetting plastics


  Once set into a shape by heat, they cannot be melted again
• Example of thermosetting plastic

  • Epoxy resins are used in adhesives and coatings
• Elastomers


  Rubber-like materials that return to their original shape after stretching
• Example of elastomer


  • Silicone rubber (such as seal windows)
• Applications of polymers


  • Construction
  • Automotive industry
  • Packaging
  • Medical applications
  • Aerospace
• Polymers in construction


  • Introduction of materials that are lightweight, durable, and resistant to corrosion
  • Easily molded into various shapes, they are ideal for insulation, piping, and flooring
• Polymers in automotive industry


  • Contribute to fuel efficiency through the production of lighter parts
  • Crafting components ranging from tires, which rely on synthetic rubber, to interior features (dashboards and seat belts)
• Polymers in packaging


  • Enable the creation of flexible films, rigid containers, and foam cushioning
  • Maintains the integrity and quality of products from food to electronics throughout their lifecycle
• Polymers in medical field

  • Create biocompatible materials for prosthetics and implants, mimicking the mechanical properties of natural tissue
  • Silicone is used for implants due to its stability and resistance to body fluids
  • The development of polymer-based hydrogels, nanoparticles, and micelles has revolutionized targeted therapies, ensuring that therapeutic compounds reach specific tissues or organs with precision
• Polymers in aerospace


  • Contribute to fuel efficiency and overall performance improvements
  • Advanced composites, made from polymers reinforced with carbon or glass fibers, form critical aircraft and spacecraft components, resisting extreme temperatures and reducing the vehicle's weight
• Production steps


  • Injection Molding
  • Blow Molding
  • Extruding
  • Overmolding