Cycloaliphatic Polymers via Late Transition Metal Catalysis - Late Transition Metal Polymerization Catalysis - page 124

given level (mol%) of co-monomer, the longer the alkyl chain the lower the T g .
Typical results using naked nickel for the copolymerization of norbornene with
varying levels of 5-decylnorbornene are presented in Tab. 4.1. The exact T g de-
pends on the molecular weight of the polymer as well as the composition. For ex-
ample, runs 4, 8, and 9 yielded polymer with similar glass transition tempera-
tures: 265-285 C. However, the lower T g is achieved in two different ways: either

by incorporating substantial quantities 5-decylnorbornene (run 4), by lowering the
molecular weight (run 9), or both (run 8). The effect of mol% 5-decylnorbornene
on T g is given in Fig. 4.22 for copolymers of similar molecular weights.
The T g of the resulting polymers can be steered in this way to any desired value
between the T g of the two homopolymers involved by adjusting the level of co-mono-
mer employed. The T g of homo(polynorbornene) is around 370-390

C. The mea-

sured T g of 5-decylnorbornene homopolymer is around 150-160 C. Longer alkyl

substituents (e.g. hexadecylnorbornene) have a more pronounced impact on T g .

4.2.3.9 Multi-Component Catalyst Systems
Having found active single-component catalysts we sought more cost-effective sys-
tems, and systems which were more effective in the copolymerization of 5-alkyl-
norbornenes (which significantly reduce the effectiveness of the naked nickel cata-
lyst when higher levels of the co-monomer are employed). We quickly discovered
that a large variety of “multi-component” or “Ziegler-type” catalyst systems based
on simple nickel salts showed good activity in the polymerization of norbornene
and alkyl-substituted norbornenes. The simplest systems of all comprised nickel
salts in combination with alkylaluminum halides. The preferred alkylaluminum
halides are the more Lewis acidic compounds, such as ethylaluminum dichloride,
or other alkylaluminums in the presence of chlorinating agents such as hexa-
chloroacetone. Presumably the net effect of the catalyst components is to generate
an alkylated cationic nickel species in combination with a weakly coordinating
chlorinated aluminum anion.
Particularly effective were the multi-component nickel systems derived from a
commercial catalyst first described and developed by Bridgestone Tire Company
for the manufacture of to make cis -1,4-polybutadiene [48]. The Bridgestone system
is the reaction product of Ni(O 2 CR) 2 (R=2-ethylhexyl), BF 3 ·Et 2 O, and AlEt 3 . Our
interest was drawn to this system by the elegant mechanistic studies of Taube [32]
who, for around 20 years, has studied model compounds in an attempt at under-
standing the nature of the active species in the industrial catalyst system. The re-
action of Ni(O 2 CR) 2 ,BF 3 ·Et 2 O, and AlEt 3 in a 1 : 9 : 10 molar ratio is thought to
initially form an unstable Ni(C 2 H 5 ) 2 intermediate along with AlF 3 which acts as a
colloidal support for the co-formed nickel species. The Ni(C 2 H 5 ) 2 intermediate de-
composes to form Ni(0), along with ethylene and ethane. The Ni(0) reacts with
butadiene along documented lines to form Ni(C 12 H 18 ). This catalyst formation
chemistry is presented in Scheme 4.1.
The C 12 H 18 ligand is formed from trimerization of butadiene and is composed
of two allyl functions and one olefin moiety. These functionalities coordinate to