Chemistry Reference
In-Depth Information
O'Driscoll [
407
] developed the kinetics of ionic copolymerization of dissimilar monomers. It is
based on the assumption, that the ratio of monomers in the copolymer d[
M
2
] is directly
proportional to the square of the initial monomer rate ([M
1
]/[M
2
])
2
in the copolymerization reaction.
M
1
]/d[
2
d
½
M
1
=
d
½
M
2
¼ðk
1
=k
2
Þðk
11
=k
22
Þð½
M
1
=½
M
2
Þ
The above shown equation was derived on the assumption that initial homopropagation is fast,
relative to the propagation. Also, that the crossover reaction is negligible at the beginning of the
copolymerization.
4.9 Group Transfer Polymerization
This technology offers considerable promise for commercial preparations of living polymers of
methyl methacrylate without resorting to low temperature anionic polymerizations. Although the
mechanism or polymerization is not completely explained, the propagation is generally believed to be
covalent
in character. A silyl ketene acetal is the initiator. It forms from an ester enolate [
391
]:
O
O
Li
+
N
Li
OCH
3
2
OCH
3
Si
Cl
O
Si
OCH
3
The initiation, that is catalyzed by either a nucleophilic or by a Lewis acid catalyst, was explained
as consisting of a concerted attack by the ketene acetal on the monomer [
392
]:
O
OCH
3
O
OCH
3
O
O
Si
Si
O
OCH
3
This results in a transfer of the silyl ketene acetal center to the monomer. The process is repeated in
each step of the propagation. The ketone double bond acts as the propagating center [
391
].
O
OCH
3
O
OCH
3
Si
Si
O
n
O
O
n
+1
O
OCH
3
O
OCH
3
O
