Thermoplastics

• Thermoplastics

  • Soften readily on heating because intermolecular forces between the polymer chains can break easily by heat
  • Can be reshaped and reused -> easy to recycle
  • Usually soft, weak and less brittle
  • Usually soluble in suitable solvents
• Most commercially important commodity thermoplastics


  • Polyolefins (polyethylene and polypropylene)
  • Polyvinylchloride (PVC)
  • Styrenics (E.g PS, HIPS)
  • Poly (ethylene terephthalate) (PET)
• Polyethylene (PE)


  • Semi-crystalline polymer
  • Three grades: LDPE, LLDPE, HDPE
  • LDPE has long-branched chains, LLDPE has short-branched chains, HDPE has linear chains
• LDPE

  • More flexible due to lower crystallinity, hence weaker intermolecular forces
  • Good transparency since it is more amorphous (Less regions to block light)
  • Lower melting temperature
  • Applications: Plastic packaging, such as for grocery bags or plastic wrap
• HDPE

  • More rigid due to higher crystallinity, hence stronger intermolecular forces
  • Less transparent as it is more crystalline (Crystalline deflect light)
  • Applications: Pipes, toys, plastic chairs, packaging bottles
• Polypropylene (PP)


  • Semi-crystalline polymer
  • Can form three basic chain structures: isotactic, syndiotactic, atactic
  • Most commercially available PP is isotactic
• Isotactic PP

  • Methyl groups (CH3) arranged on same side of the carbon chain
  • Closely packed chains
• Polyvinylchloride (PVC)


  • Formed through addition polymerization of the chloroethene monomer
  • Commercial PVC is a clear, moderately tough, low-crystallinity with melting temperature at 212°C
  • Available in two grades: rigid and flexible
• 2 main types of commodity styrenic polymers

  • General purpose polystyrene (GP-PS)
  • High impact polystyrene (HIPS)
• GP-PS

  • Formed through addition polymerization of the styrene monomer
  • Transparent and brittle
• HIPS

  • Graft copolymer of styrene and butadiene
  • Opaque and high impact strength due to butadiene chain
• Polyethylene Terephthalate (PET)


  • Condensation (esterification) reaction between terephthalic acid and ethylene glycol
  • Highly flexible, colorless and semi-crystalline resin in its natural state
  • One of the most recycled thermoplastics
• Recycled PET can be converted to fibers, fabrics, sheets for packaging and manufacturing automotive parts