Control of branch formation in ethylene polymerization by a [Ni(h3-2-MeC3H4)(diimine)] PF6 / DEAC catalyst system

The polymerization of ethylene mediated by [Ni(eta3-2-MeC3H4){ArN=C(H)C(H)=NAr}] PF6, Ar = 2,6-C6H3iPr2 /DEAC catalyst precursor under mild reaction conditions (reaction temperature between -10 oC and 25 oC and ethylene pressure between 109 and 1520 kPa) yields high molecular weight branched polyethylene. The degree of branching was modulated by a careful choice of reaction conditions. Thus, at 0 oC and 109 kPa, the branching degree was 17 branches/1000 backbone carbon atoms and at 25 oC, it went up to 90 branches/1000 backbone carbon atoms. The nature of the observed branches (methyl, ethyl and longer), their quantity and distribution along the polymer backbone chain can be rationalized in terms of a chain walking process and control of the extend of isomerization by the steric hindrance of the growing chain.