Definition: Polymerisation is a chemical reaction where small molecules called monomers join to form long-chain molecules known as polymers.

Types of Polymers

1. Natural Polymers
   • Found in living organisms.
   • Examples:
     • Proteins
     • Carbohydrates
     • Starch
     • Wood
     • Rubber
     • DNA
2. Synthetic Polymers
   • Manufactured in industries, often referred to as plastics.
   • Examples:
     • Polythene
     • Polyvinylchloride (PVC)
     • Terylene
     • Nylon
     • Perspex (artificial glass)
     • Polytetrafluoroethylene (PTFE or Teflon)
     • Polystyrene

Types of Polymerisation

1. Addition Polymerisation
   • Involves the repeated addition of monomers of the same type.
   • Monomers used are usually unsaturated compounds (e.g., ethene).
   • Example:
     • Polymerisation of Ethene:
       • n C2H4→(C2H4)n (polyethene)
     • Conditions: High temperature, high pressure, and a catalyst.
     • The double bonds between carbon atoms break, allowing the monomers to link.
2. Condensation Polymerisation
   • Involves the reaction of two different monomers, resulting in the elimination of a small molecule (e.g., water or hydrogen chloride).
   • Example:
     • Esterification:
       • Carboxylic acid + Alkanol → Ester + Water
   • Examples of Condensation Polymers: Nylon, Terylene (polyester).

Properties of Synthetic Polymers

• Corrosion Resistance: Do not corrode in air or water.
• Insulation: Excellent heat and electrical insulators.
• Stability: Do not decompose easily.
• Lightweight: Relatively light compared to other materials.
• Transparency: Some are transparent, making them suitable for various applications

Uses of Synthetic Polymers

1. Polyethene (from Ethene)
   • Uses:
     • Pipes and plastic bags
     • Bowls and bottles
     • Packaging material
     • Insulation for electrical wiring
2. Polyvinylchloride (PVC) (from Chloroethene)
   • Uses:
     • Crates and bottles
     • Plastic ropes
     • Artificial leather
     • Water pipes
     • Insulation for electrical wiring
3. Polystyrene (from Styrene)
   • Uses:
     • Insulation material
     • Packaging (foam)
     • Radio cabinets
     • Pot handles
4. Polytetrafluoroethylene (PTFE or Teflon) (from Tetrafluoroethene)
   • Uses:
     • Soles of iron
     • Non-stick frying pans
5. Perspex
   • Uses:
     • Glass substitute
     • Lenses

Advantages of Synthetic Polymers

• Cheap to produce
• Resistant to corrosion from acids, alkalis, water, and air
• Lightweight and portable
• Soft and easy to manufacture
• Easily molded into complicated shapes
• Good heat insulators
• Good electrical insulators

Disadvantages of Synthetic Polymers

• Non-biodegradable, making disposal difficult
• Some release toxic gases (e.g., carbon monoxide) when burned
• Expensive to recycle
• Some are flammable

Types of Plastics

1. Thermoplastics (Thermosoftening Plastics)
   • Characteristics:
     • Soften when heated and harden into new shapes when cooled
     • Weak intermolecular forces; no cross-links between polymer chains
   • Examples: Polythene, PVC, Polystyrene
   • Properties:
     • Flexible and do not break easily
     • Can be molded multiple times
     • Low melting points
     • Easily recyclable
2. Thermosetting Plastics (Thermosets)
   • Characteristics:
     • Set hard and cannot be melted again after formation
     • Strongly held polymer chains due to cross-links
   • Examples: Melamine, Formica, Bakelite
   • Properties:
     • Rigid and break under tension rather than stretch
     • Cannot be molded into new shapes after creation
     • Decompose on heating instead of melting
     • Not recyclable

Differences Between Thermoplastics and Thermosetting Plastics

• Heating Behavior:
  • Thermoplastics soften and melt when heated, allowing them to be reshaped multiple times.
  • Thermosetting plastics do not soften on heating; they retain their shape permanently.
• Molding Capability:
  • Thermoplastics can be re-molded into new shapes after they are made.
  • Thermosetting plastics cannot be re-molded once set.
• Molecular Structure:
  • Thermoplastics have no cross-links between their polymer chains, resulting in weaker intermolecular forces.
  • Thermosetting plastics have cross-links between their polymer chains, making them more rigid and strong.
• Recyclability:
  • Thermoplastics can be recycled.
  • Thermosetting plastics cannot be recycled due to their rigid structure.