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2) Initiation: Initiator added, bonds break and radicals are formed

PLEASE NOTE: For the exam you need to be able to describe what the steps: Initiation, propagation and termination mean and put them in order (see next slide). Low Density Polyethylene is manufactured using a free radical mechanism (initiated with a peroxide initiator) under high pressure.

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2) Initiation: Initiator added, bonds break and radicals are formed

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  1. PLEASE NOTE: For the exam you need to be able to describe what the steps: Initiation, propagation and termination mean and put them in order (see next slide) Low Density Polyethylene is manufactured using a free radical mechanism (initiated with a peroxide initiator) under high pressure.

  2. 2) Initiation: Initiator added, bonds break and radicals are formed 3) Free radicals + monomers 1)Monomers 4) Propagation: monomers join to radical; chain grows. 6) Termination: Long chain radicals join. Polymer formed. . 7)Complete polymer 5) Long chain radicals + monomers

  3. PLEASE NOTE: You DO NOT need to be able to recall the detail on the remaining slides, though it will help you to understand how the process works.

  4. Low Density Polyethylene In the initiation stage, radicals are made using an organic peroxide catalyst.

  5. Low Density Polyethylene: Initiation The O–O bond is weak and breaks to make R–O radicals (alkoxy radicals).

  6. Low Density Polyethylene An alkoxy radical combines with one of the electrons from the double bond in ethylene.

  7. Low Density Polyethylene: Propagation An alkoxy radical combines with one of the electrons from the double bond in ethylene.

  8. Low Density Polyethylene: Propagation This forms a new covalent bond and a new radical.

  9. Low Density Polyethylene: Propagation The new radical reacts with another ethylene molecule.

  10. Low Density Polyethylene: Propagation This forms another new radical, longer than before.

  11. Low Density Polyethylene The chain grows longer until two radicals react with each other.

  12. Low Density Polyethylene: Termination This is called the termination step.

  13. Low Density Polyethylene: Branched chains A growing chain may curl around and attack itself by back-biting.

  14. Low Density Polyethylene: Branched chains The radical moves to another part of the chain, and allows branched chains to grow from the side.

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