Polymers

Polymers are large molecules formed from many smaller, repeating units called monomers, joined together by covalent bonds.

Monomers

Monomers are the building blocks of polymers. A monomer must have at least two reactive sites (functional groups) to join with others. Monomers may have double or triple bonds to allow polymer formation.

Polymerization

Polymerization is the chemical process that links monomers to form large macromolecules known as polymers. This process usually requires high temperature, high pressure, and an initiator like oxygen or organic peroxide.

Types of Polymerization:
- Homopolymerization: All monomers are identical.
- Copolymerization: Involves two or more different monomers.

Types of Polymerization

  1. Addition Polymerization: Involves a reaction between unsaturated monomers like ethene. For example:
    n(CH2=CH2) → (-CH2-CH2-)n
    Conditions: High temperature (250°C) and high pressure (150 atm)
  2. Examples of addition polymers include:

    • Polythene – used for producing films, sheeting, bags, and wrappers.
    • Polypropylene – commonly used in the manufacture of ropes.
    • Polystyrene – used in making electrical insulators, toys, shoe soles, and dishes.
    • Polybutylene – primarily used in car tire production.
    • Perspex – used as a glass substitute.
    • Polyvinylchloride (PVC) – applied in coating fabrics, wire and cable insulation, and gramophone records.
    • Acrilan – used in textile manufacturing.
  3. Condensation Polymerization: Involves monomers reacting and releasing a small molecule like water. Typically involves two different monomers. Many natural polymers are formed this way.

Synthetic Polymers

Synthetic polymers are man-made materials created through industrial processes using chemical substances. Scientists replicate the structure of natural polymers to produce these synthetic variants. Most of the raw materials used in their production come from petroleum after refining and cracking.

Types of synthetic polymers include:

Elastomers

Elastomers are polymers that return to their original shape after being stretched or compressed. Natural rubber and synthetic rubber (e.g. neoprene and styrene-butadiene rubber (SBR)) are examples. SBR is commonly used in manufacturing car tyres.

Properties of Polymers

Uses of Polymers

  1. Polystyrene: Used for transparent containers, shock-absorbing packaging, disposable cups, and food containers.
  2. Poly(propenonitrile): Spun into threads for wool-like garments (e.g., Orlon).
  3. Perspex: Used as a glass substitute for car lights, windows, aquariums, contact lenses, and streetlamps.
  4. Nylon: Used in making ropes, fishing lines, nets, and clothes that are quick-drying, crease-free, and resistant to pests.
  5. Terylene: Woven into rot-proof fabrics like boat sails.