Heterogeneous catalysts prepared by loading homogeneous α-diimide nickel complexes with asymmetric N-aryl substituents onto carbon nanotubes for 1,3-butadiene polymerization

Inexpensive and reusable transition metal heterogeneous catalysts demonstrate excellent polybutadiene performance and are appealing substitutes for precious metal and homogeneous catalysts. Here, a variety of homogeneous nickel catalysts were designed and synthesized by a two-step Schiff base reaction involving dinaphthones and different aniline derivatives. These homogeneous nickel catalysts are also known as novel α-diimine ligands with asymmetric N-aryl substituents (Ni1-Ni3). Under the optimal reaction conditions ([BD]/[Ni] = 6000, [Al]/[Ni] = 600, 0 °C, 4 h), Ni3 exhibited the best catalytic effect (PBD yields obtained averaged 96.5 %). The PBD in question possesses a molecular weight of 5.53 × 10⁴. The cis-structural ratio aligns with the Ziegler-Natta catalytic system. The corresponding heterogeneous nickel catalysts (Ni1/CNT-Ni3/CNT) were prepared by attaching these ligands to the carbon nanotube surfaces via amidation reactions of carboxyl and amino groups. Under the optimal conditions, Ni3/CNT exhibited the best catalytic effect (the obtained PBD yield reached 99.4 % on average). The PBD in question possess a molecular weight of 5.30 × 10⁴. No significant decrease in activity was observed after five reuse cycles. The homogeneous catalyst (Ni3/CNT) prepared in this experiment not only improves production efficiency and economic benefits but also reduces energy consumption and environmental pollution.