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3
25
C [10]! However, the polymerization rate was found to decrease dramatically
for norbornene derivatives with pendant oxygen functionalities on the side oppo-
site to the C=C bond (Tab. 9.1) [10].
Based on the 13C-NMR shifts, one can surmise that the electronic effect of the
substituent on the C=C bond is minimal. Thus, the vinyl carbons of the norbor-
nene resonate at 135.5 ppm, while those of 5-norbornene-2-carboxylic acid ethyl
ester appear at 137.7 and 132.5 ppm (
endo
) and 138.1 and 135.9 ppm (exo).
Because they are synthesized by Diels-Alder reaction, functionalized norbornene
derivatives sold commercially consist of
exo
and
endo
isomers with the latter pre-
dominating. The drop in polymerization rate for functionalized norbornene deri-
vatives may be ascribed to the formation of a chelate by coordination of the metal
to the functionality and the C=C bond along the
endo
face (see Fig. 9.2).
Tab. 9.1
Polymerization results with palladium(II) complex [10].
Yield [%] M
w
a)
Monomer
“Pd(PPh
3
)
(CH
3
)”
[mol]
Monomer
[mol]
Reaction
time
Temp.
[
C]
10
-7
3.02
0.106
<2 min 25
100
Insoluble
10
-5
7.56
0.053
2 min 25
100
212900
2.94
10
-5
0.012
24 h
60
40
6500
10
-5
2.94
0.010
24 h
60
38
6400
a)
Obtained relative to polystyrene standards in CHCl
3
.
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