So far, ligand steric effects of the α-diimine nickel catalysts on the polyolefin branching densities are not systematically investigated. Generally, in contrast to the α-diimine palladium systems, the branching densities of the polyethylene obtained by the α-diimine nickel catalysts increased when the more sterically encumbering substituent was employed. In this contribution, we described the synthesis and characterization of a series of α-diimine ligands and the corresponding nickel catalysts bearing the diarylmethyl moiety and varied steric ligands. In ethylene polymerization, the catalytic activities [(2.82–15.68) × 106 g/(mol Ni·h)], polymer molecular weights [M n: (0.37–131.51) × 104 g mol–1], branching densities [(28–81)/1000 C], and polymer melting temperatures (−4.7–122.9 °C) can be tuned over a very wide range. To our surprise, the polymer branching density first rose and then fell when we systematically increased the steric bulk of α-diimine nickel catalysts, like a downward parabola, not in line with previous conclusions. In ethylene-methyl 10-undecenoate (E-UA) copolymerization, the catalytic activities [(1.0 × 103) – (104.8 × 104) g/(mol Ni·h)], copolymer molecular weights [(1.2 × 103) – (242.4 × 103) g mol–1], branching densities [(42–70)/1000 C], and UA incorporation ratio (0.17–2.12%) can also be controlled over a very wide range. The tuning in steric ligands enables the tuning of the polymer microstructures such as molecular weight and branching density. In this way, the best polyethylene elastomer catalysts are screened out.

No abstract

No abstract

Isotactic poly(1-butene)s (iPBs) were synthesized via bulk polymerization of 1-butene in the presence of a series of nucleating agents (NAs). The effects of the NAs on the polymerization, crystallization and mechanical properties of the resultant iPBs were systematically investigated. Both ⊍and ⊎-NAs effectively improve the impact resistance of iPB. Specifically, the addition of ⊎-NAs increases the molecular weight, tensile strength, elastic and flexural moduli of iPB without affecting catalytic activity during polymerization, while the ⊍-NAs have no affirmative effect on improving the tensile strength and elastic modulus of iPB. The ⊎-NAs also accelerate the crystal transition rate of iPB from form II to form I.