Polymerisation

🔹 1. What is Addition Polymerisation?

Addition polymerisation is a type of polymerisation in which unsaturated monomers (usually alkenes) join together without the elimination of any small molecule.

• The reaction involves breaking the π bond in the alkene and forming new C–C single bonds to connect the monomers.

➡️ Key Condition:

• Requires high temperature, high pressure, and a catalyst (e.g., peroxide initiators).

🔹 2. Examples of Addition Polymers

✅ Poly(ethene) (commonly known as Polythene)

• Monomer: Ethene (CH₂=CH₂)
• Polymer: Poly(ethene)

Equation:

 n CH₂=CH₂ → –[CH₂–CH₂]–ₙ

✅ Poly(chloroethene) or PVC (Polyvinyl chloride)

• Monomer: Chloroethene (CH₂=CHCl)
• Polymer: Poly(chloroethene)

Equation:

 n CH₂=CHCl → –[CH₂–CHCl]–ₙ

Note:

• PVC is used in pipes, wires, and plastic doors/windows.

🔹 3. Deduce the Repeat Unit of an Addition Polymer

To find the repeat unit:

• Identify the alkene monomer (usually has a C=C double bond).
• Break the double bond, and form a single bond connecting to other units.
• Show the two carbon atoms from the monomer with their substituents, and extend bonds on each side to show repetition.

Example:
From ethene (CH₂=CH₂), the repeat unit is:
 –CH₂–CH₂–

🔹 4. Identify the Monomer from a Polymer

To identify the monomer:

• Look at two adjacent repeat units in the polymer.
• Insert a C=C double bond between the two central carbon atoms.
• Reconnect the side groups accordingly.

Example:
Given polymer unit: –CH₂–CHCl–
Monomer: Chloroethene (CH₂=CHCl)

🔹 5. Problems with Disposal of Poly(alkene)s

Poly(alkene)s like poly(ethene), poly(propene), and PVC are non-biodegradable, meaning:

❌ Not broken down naturally

• Microorganisms cannot digest them.
• Accumulate in the environment (landfills, oceans).

❌ Combustion Issues

• Burning these plastics produces toxic gases:
  • Poly(chloroethene) (PVC) releases hydrogen chloride (HCl), a corrosive and harmful gas.
  • Incomplete combustion releases carbon monoxide (CO).

🔁 Sustainable Disposal Options:

• Recycling
• Incineration with gas scrubbers
• Development of biodegradable alternatives

💡 Quick Recap Table

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