Advices For Studying Organic Chemistry

A Mechanism for the Reaction

Radical Polymerization of Ethene
Chain Initiation

Step 1

CCOO^2 CO

O

R

O

R

O

R 2CO 2 +^2 R

Diacyl peroxide (^)
Step 2 R +H^2 CCH^2 R CH^2 CH^2
The diacyl peroxide dissociates to produce radicals, which in turn initiate chains.
Chain Propagation
Step 3 R CH^2 CH^2 + nH^2 CCH^2 R ( )CH^2 CH^2 nCH^2 CH^2
Chain propagation by adding successive ethylene units, until their growth is stopped
by combination or disproportionation.
Chain Termination
Step 4
2 R ( )CH 2 CH 2 nCH 2 CH 2
combination
disproportionation
R ( )CH 2 CH 2 nCH 2 CH (^22)
R ( )CH 2 CH 2 nCH CH 2 +
R ( )CH 2 CH 2 nCH 2 CH (^3)
The radical at the end of the growing polymer chain can also abstract a hydrogen
atom from itself by what is called “back biting.” This leads to chain branching.
Chain Branching
R CH 2 CH
CH 2 CH 2
CH 2
CH 2
( )n
H
H
H
RCH 2 CH ( )CH 2 CH 2 nCH 2 CH 2
H 2 CCH 2
RCH 2 CH ( )CH 2 CH 2 nCH 2 CH 2
CH 2
CH 2 etc.