Mono‐ and binuclear nickel catalysts for 1‐hexene polymerization

Polymerization of 1‐hexene was carried out using a mononuclear (MN) catalyst and two binuclear (BN1 and BN2) α‐diimine Ni‐based catalysts synthesized under controlled conditions. Ethylaluminium sesquichloride (EASC) was used as an efficient activator under various polymerization conditions. The highly active BN2 catalyst (2372 g poly(1‐hexene) (PH) mmol−1 cat) in comparison to BN1 (920 g PH mmol−1 cat) and the MN catalyst (819 g PH mmol−1 cat) resulted in the highest viscosity‐average molecular weight (Mv) of polymer. Moreover, the molecular weight distribution (MWD) of PH obtained using BN2/EASC was slightly broader than those obtained using BN1 and MN (2.46 for BN2 versus 2.30 and 1.96 for BN1 and MN, respectively). These results, along with the highest extent of chain walking for BN2, were attributed to steric, nuclearity and electronic effects of the catalyst structures which could control the catalyst behaviour. Differential scanning calorimetry showed that the glass transition temperatures of polymers were in the range − 58 to −81 °C, and broad melting peaks below and above 0 °C were also observed. In addition, longer α‐olefins (1‐octene and 1‐decene) were polymerized and characterized, for which higher yield, conversion and molecular weight were observed with a narrower MWD. The polymerization parameters such as polymerization time and polymerization temperature showed a significant influence on the productivity of the catalysts and Mv of samples. Synthesis of poly(1‐hexene) was carried out using a mononuclear and two binuclear α‐diimine Ni‐based catalysts. Substantial effects of steric, nuclearity and electronic features of ligand and complex structure along with reaction conditions for catalyst BN2 led to higher Mv, broader molecular weight distribution, higher level of chain walking and broader melting area.