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
- 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) - 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.
- Condensation Polymerization: Involves monomers reacting and releasing a small molecule like water. Typically involves two different monomers. Many natural polymers are formed this way.
Examples of addition polymers include:
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:
- Plastics
- Fibres
- Elastomers
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
- Polymers like plastics are lightweight, durable, and resistant to air, water, chemicals, fungi, and bacteria.
- They can be manufactured in various forms—hard blocks, flexible sheets, fibres, or foams.
- Polystyrene: A clear, brittle plastic used to create Styrofoam when mixed with air and a foaming agent.
- Perspex: A strong, hard, transparent thermoplastic with a glossy surface.
- Nylon: Known for its high tensile strength, ideal for fibres.
- Terylene: A soft fibre that retains permanent creases well.
Uses of Polymers
- Polystyrene: Used for transparent containers, shock-absorbing packaging, disposable cups, and food containers.
- Poly(propenonitrile): Spun into threads for wool-like garments (e.g., Orlon).
- Perspex: Used as a glass substitute for car lights, windows, aquariums, contact lenses, and streetlamps.
- Nylon: Used in making ropes, fishing lines, nets, and clothes that are quick-drying, crease-free, and resistant to pests.
- Terylene: Woven into rot-proof fabrics like boat sails.