HS2004_2339 Week 4 Asyn_Mechansisms of Decay in polymers

Question 1

How free radicals create more free radicals

Answer 1

Question 2

What is a free radical

Answer 2

Question 3

Diagram showing how different energies are required for free radical production

Answer 3

Question 4

Scheme of reaction of free radicals

Answer 4

Question 5

Free radicals in polymer chains: stage one: Abstraction: free radicals

Answer 5

• an attack on the C-H bond, producing two free radicals, one on the carbon chain

Question 6

Stage two of free radical production on polymer chains (formation of a peroxy radical)

Answer 6

• hydrogen abstracted, creating a free radical, this is how polymers decay
• this can react with oxygen, to stabilise via covalent bonding, but the oxygen remains a free radical (this is called a peroxy radical)

Question 7

Stage three of free radical production in polymers: Abstraction

Answer 7

A weaker hydrogen bond is targeted, and pulled in

Question 8

Free radical oxyl group causing chain scission (diagram)

Answer 8

• creates an oxyl radical
• reaction depends on energy and structure

Question 9

Polymer decay reactions, which are non free- radical and non homolytic

Answer 9

Question 10

Diagram showing side chain loss in polyvinyl acetate- what is the Physical change?

Answer 10

yellowing in polymer

Question 11

Diagram of cyclisation in polymer decay

Answer 11

Question 12

How heat and oxygen causes degradation of polymers and free radical formation

Answer 12