Steric and electronic effects in cationic pyridine carboxamidate nickel mediated ethylene polymerization and copolymerization with methyl 10-undecenoate

Abstract

Improvement of catalysts performance by structural modification is a well recognised and more reliable way in catalysis. Amide derived catalysts were already used in olefin polymerization but possessed many limitation regarding to their poor thermal stability and mostly generating low molecular weight oligomers. Steric and electronic factors have played a characteristic role to control the catalyst stability, activity, molecular weight and branch densities of the polymers. So in continuity of our interest to improve the performance of olefin polymerization catalysts, we contributed here by synthesized cationic nickel catalysts (Ni1–Ni3) by simple amidation of picolinoyl chloride with sterically bulky and electronically varied anilines. Effect of steric and electronic factors also has been explored. Compared with previously reported sterically open pyridine carboxamidate nickel catalysts, these bulky nickel catalysts have two orders of magnitude higher activity of up to 3.73× 106 g (mol Ni)−1 h−1 towards ethylene polymerization and thermal stability up to 80 °C, producing higher molecular weight semi-crystalline polyethylene with tunable branching densities (17–67 branches/1000C) and melting points (65–121 °C). Moreover, these cationic nickel catalysts also promote the copolymerization of ethylene and methyl 10-undecenoate (MU) to afford polar functionalized polyethylenes with maximum incorporation of MU up to 1.53 mol%.