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naked palladium. The following example from a recent patent application [64]
serves to illustrate the very high activity of such catalysts:
To a thick-walled, septum-sealed glass vial, equipped with a magnetic stir-bar
was added 5-butylnorbornene (7.95 g, 53 mmol), toluene (19 mL), palladium ethyl
hexanoate (82
L, 0.35
mol), tricyclohexylphosphine (28
L, 0.35
mol), trispenta-
fluorophenylboron (126
L, 6.36
mol) and triethylaluminum (4.2
L (1.7 M in
cyclohexane), 7.0
mol) (ratio of monomer to palladium, 150000 : 1). The resulting
stirred solution was placed in a heated oil bath at 67
C for a total of 3 h. Within
less than 30 min the colorless, clear solution was a highly viscous mass that could
no longer be stirred. After 3 h the colorless gel was isolated by breaking the flask,
was cut into small pieces using a blade and the material was dissolved in boiling
toluene (800 mL) over a period of several hours. The polymer was precipitated by
pouring into excess methanol (1 L), filtered off and washed with excess methanol
prior to drying to constant weight under vacuum at 80
C. The dried, white, gran-
ular polymer was found to weigh 7.76 g (97.6% conversion).
In this patent application are also described many examples of “well-defined”
catalysts made by reacting one mole of the desired phosphine with allylpalladium
chloride dimer and then activating the resulting complex with a suitable activator.
Preferred activators are weakly coordinating anion salts capable of abstracting a
halide (e.g. the lithium salt of tetrakis(pentafluorophenyl)borate). The activator is
typically applied in a 5 molar excess on palladium to ensure complete activation.
Preferred phosphines are hindered, strongly donating examples such as tricyclo-
hexylphosphine and tritolylphosphine. These highly active catalysts also proved to
be the ideal systems to allow the realization of RIM (reaction injection molding)
of norbornenes to afford completely saturated, high
T
g
poly(norbornene) parts in
a mold (Section 4.2.3.2).
4.2.3.10
Polymerization of Norbornenes Containing Functional Groups
The (co-)polymerization of functional monomers was also explored with the Ni
and Pd catalyst systems. The multi-component Ni catalyst (Ni(O
2
CR)
2
+HSbF
6
+9BF
3
·Et
2
O+10AlEt
3
) works very well for the copolymerization of nor-
bornene and 5-triethoxysilylnorbornene. The copolymerization of norbornene and
with 5-10 mol% 5-triethoxysilylnorbornene monomers yields a high molecular
weight copolymer of the same molar composition in excellent yield (85%) at a
4000 : 1 monomer to nickel molar ratio.
The copolymers of this type were found to have very interesting adhesive, di-
electric, and optical properties. The polymers were found to adhere to substrates
such as silicon dioxide, aluminum, copper, and even gold. Even more surprisingly,
the polymer film cast on gold did not delaminate even after exposure to boiling
water for 2 h. The refractive index of this polymer was around 1.51 and the bire-
fringence was low (
n
=0.0014). The electrical permittivity was also low (ca. 2.5).
All of these properties, coupled with the inherently high glass transition tempera-
ture, make the materials attractive for electronic and optical applications [65].
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