Chemistry Reference
In-Depth Information
CHAIN GROWTH (ADDITION) POLYMERIZATION
Polymerization steps:
•
Initiation
H
R
*
+
CH
2
CH
X
R
CH
2
C*
X
• Propagation
H
H
+
n
CH
2
CH
X
R
CH
2
CH(CH
2
CH
)
n
-1
CH
2
C*
R
CH
2
C*
X
X
X
X
• Termination
H
)
n-1
*
R
CH
2
CH( CH
2
CH
CH
2
C*
+ R
′
X
X
X
R
CH
2
CH( CH
2
CH
)
n-1
CH
2
CH
X
R¢
X
X
Chain polymerization involves three steps. To start the reaction, a catalyst
that can generate an active site, such as a
(R*), is used. In the
initiation step, the radical adds to the double bond, and the radical site is
moved to the end carbon. This new radical reacts with another molecule to
give a larger radical, and the propagation reaction is underway. Usually, the
number of monomers in the chain is greater than 1000. In the above formulae,
free radical
