Engineering Science 1021A/B Lecture Notes - Lecture 33: Polyethylene, Disproportionation, Methanol
17 May 2018
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Addition Polymerization
Addition polymerization: mechanism of growing polymer chains by adding
individual repeat units to the end
Polyethylene is made this way
○
•
An initiator is used to start the chain
•
Additional repeat units add on to increase the length of the chain
•
Growth is rapid at first and slows as polymerization nears completion because
the diffusion distances for the remaining mers becomes longer
•
Benzoyl peroxide is used to form the starting link in the chain
○
•
The growing chain can be terminated in 2 ways:
Combination: Two growing chains connect
○
Disproportionation: An active chain removes a hydrogen atom from a
second chain
○
○
•
Condensation Polymerization
Linear molecules can also be formed by condensation polymerization•
This is a step process involving at least 2 different monomers•
Condensation reaction for polyethylene terephthalate (PET)
The OCH3 group and a hydrogen atom are removed from the mono-
mers, permitting the two monomers to join and producing methyl
alcohol as a byproduct
§
○
•
Both monomers are bifunctional and therefore the chains can grow in
both directions
○
•
Addition/Condensation Polymerization
Addition Polymerization
Addition polymerization: mechanism of growing polymer chains by adding
individual repeat units to the end
Polyethylene is made this way
○
•
An initiator is used to start the chain•
Additional repeat units add on to increase the length of the chain•
Growth is rapid at first and slows as polymerization nears completion because
the diffusion distances for the remaining mers becomes longer
•
Benzoyl peroxide is used to form the starting link in the chain
○
•
The growing chain can be terminated in 2 ways:
Combination: Two growing chains connect
○
Disproportionation: An active chain removes a hydrogen atom from a
second chain
○
○
•
Condensation Polymerization
Linear molecules can also be formed by condensation polymerization•
This is a step process involving at least 2 different monomers•
Condensation reaction for polyethylene terephthalate (PET)
The OCH3 group and a hydrogen atom are removed from the mono-
mers, permitting the two monomers to join and producing methyl
alcohol as a byproduct
§
○
•
Both monomers are bifunctional and therefore the chains can grow in
both directions
○
•
Addition/Condensation Polymerization
