Novel Ligand Control of PE Molecular Weight

13 dLg . Chain propagation as opposed to chain termination and chain transfer are favored by the ligand field modifications. 

We therefore looked for other (R3P-C = C-O) components in the (ylide A/ylide B/Ni) concept that would allow us to control the molecular weight to a greater extent. 

Indeed, more marked chemical changes in the PO component dramatically altered the selectivity for the PE molecular weight and led to a novel ligand-steered molecular weight control. The molecular weight increases in the ligand series 1 - 2 3 1 7 7 [Eq. (11)]. 

High temperature GPC studies who that the 20 C PE sample is monomodal and has a narrow molecular weight distribution. The polydispersity Mw/M of 2.4 indicates a single site insertion mechanism. With increasing polymerization temperature the molecular weight distribution broadens. 

Further chemical fine tuning has been achieved by means of additional ligands with ylide-type bond systems from the iso-electronic series of highly polar P-ylides, P-imines and P-oxides. Examples for HDPEs (high density polyethylenes) are given in Tab. 1.4. 

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