Polymer

• Polymers


  Large molecules from many similar units (monomers) bonded together
• Polymers


  • Polystyrene from styrene monomers
• Homopolymers


  Polymers with identical monomer units
• Copolymers


  Polymers with two or more different monomers
• Physical properties of polymers

  • Toughness, viscoelasticity, and semi-crystalline structures
• Types of polymers


  • Natural (e.g., cellulose, DNA, proteins)
  • Synthetic (e.g., polyethylene, polystyrene)
• Annual production of polymers (as of 2015)
• Both natural and synthetic polymers have high industrial importance
• Synthetic polymers


  • PET, PP, PVC derived from fossil fuels
• Natural polymers


  • Rubber, shellac, and amber
• Applications of polymers


  • Packaging
  • Fabrics
  • Plastic materials
• Classification of polymers based on origin

  • Natural
  • Semi-synthetic
  • Synthetic
• Classification of polymers based on structure

  • Linear
  • Branched
  • Cross-linked
• Classification of polymers based on molecular forces

  • Elastomers
  • Fibers
• Classification of polymers based on polymerization

  • Addition polymers
  • Condensation polymers
• Linear Polymers


  Single, continuous chains without branching
• Linear Polymers


  • Polyethylene, PVC, Nylon
• Characteristics of linear polymers

  • They can be semi-crystalline, often with both amorphous and crystalline phases
• Branched Polymers


  Polymers with side branches extending from the main chain
• Branched Polymers


  • Polypropylene, Amylopectin, Glycogen
• Characteristics of branched polymers


  • The side branches can be short (alkyl groups) or long
• Cross-linked Polymers


  Polymers with chains connected by bonds forming a network structure
• Cross-linked Polymers


  • Bakelite, Vulcanized rubber
• Characteristics of semi-crystalline cross-linked polymers


  • They have regions where the chains pack in an ordered manner
• Slightly Cross-linked Polymers (Elastomers)


  Polymers with flexible cross-links that can stretch and return to original shape
• Characteristics of slightly cross-linked polymers (elastomers)


  • Wide-meshed cross-linking, they are soft and elastic at room temperature
• Highly Cross-linked Polymers (Thermosets)


  Polymers with a rigid, 3D network of bonds
• Characteristics of highly cross-linked polymers (thermosets)


  • They are amorphous and cannot be remolded once set
• Elastomers


  Stretchy polymers with high viscoelasticity and weak intermolecular forces. They return to their original shape after stretching.
• Elastomers


  • Natural rubber
• Thermoplastics


  Soften when heated and harden when cooled. This process is reversible, allowing for remolding and recycling.
• Thermoplastics


  • Polyacrylonitrile
• Thermosetting Polymers


  Harden upon heating and cannot be remelted. They undergo a permanent chemical change when first set.
• Thermosetting Polymers


  • Bakelite
• Addition Polymerization


  Also known as chain-growth polymerization. Forms polymer through generation of free radicals or ions.
• Condensation Polymerization


  Also known as step-growth polymerization. Monomer units' functional groups react to form polymer.
• Polystyrene Chain Growth Polymerization

  • Monomer: Ethenylbenzene (Styrene)
  • Derived from petrochemicals
  • Used to produce transparent plastic for containers, cutlery, etc.
• Expanded Polystyrene (EPS)


  • Produced by adding gas during production
  • Used for insulation, packaging, and flotation devices
• Chemical properties of polystyrene

  • Chemically inert, resistant to acids and bases
  • Soluble in chlorinated solvents
  • Slow to biodegrade
• Polystyrene Polymerization Mechanism


  1. Initiation: Benzoyl peroxide initiates free radical polymerization

  2. Propagation: Styrene polymerizes via free radical mechanism, building up polymer chain

  3. Termination: Polymerization halted at desired length or molecular weight