Ligand effects on chain length Oligomers

In the above we have seen that very subtle changes in steric and electronic properties of the ligands can influence the rates of insertion and chain transfer reactions. Especially the rates of change transfer span a range of many orders of magnitude there may be live orders of magnitude between the alcoholysis rates of systems based on bdompp and dtbpx. 

So far we have only discussed catalysts based on diphosphine ligands with a focus on ethene. We should mention that the ligands that are most effective for this reaction are also capable of making terpolymers of ethene, propene and CO. This is important because the commercially interesting polymers must contain a few percent of propene in order to lower the melting point to around 

220 °C. The high melting point of pure ethene/CO (265 °C) gives decomposition and formation of brown, fiiranised polymers in the melt, which makes processing in extruders impossible. 

The insertion rate of propene is about twenty times lower than that of ethene, and thus the propene concentration has to be relatively high in order to obtain a few percent of incorporation in the terpolymer [2,9], 

The styrene/CO polymers formed with palladium complexes of diimine ligands indeed contain ester and alkene end groups [65,66,67], Slightly more ester end groups than alkene groups are formed, showing that in addition to P-hydride elimination some termination via methanolysis of acylpalladium chain ends occurs. 

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