Cycloaliphatic Polymers via Late Transition Metal Catalysis - Late Transition Metal Polymerization Catalysis - page 147

Fig. 4.36 Ligands used in the palladium-catalyzed copolymerization
of ethylene with norbornenes.
800000) resulted when appropriately substituted diimine ligands were employed.
The scope of the ligands exemplified [89] is illustrated in Fig. 4.36.
The structure of the di-imine ligand has a dramatic effect on the structure and
properties of the copolymer formed. Firstly the phenyl rings must bear ortho-sub-
stituents in order to generate higher molecular weight polymer, just as in the case
of the ethylene polymerization systems [20]. However, the presence or absence of
substituents on the bridge or backbone of the ligand is absolutely critical in deter-
mining the level of norbornene that can be incorporated. This is illustrated in
Fig. 4.37 where it can be seen that introducing methyl groups on to the backbone
(on an otherwise identical ligand) lowers the norbornene incorporation from
around 85 mol% to around 45 mol% with a simultaneous drop in T g from around