Bijal Kottukkal Bahuleyan

Polymerization of methyl methacrylate by sterically modulated bis(salicylaldiminate)-cobalt(II) complexes combined with methylaluminoxane

ConclusionsA series of sterically modulated bis(salicylaldiminate) cobalt(II) complexes were synthesized and applied to the polymerization of MMA in the presence of MAO as a cocatalyst. All catalysts showed moderate activities and yielded syndiotactic-rich PMMA with syndiotacticity more than 73.5%.

Morphology-tunable architectures constructed by supramolecular assemblies of α-diimine compound: fabrication and application as multifunctional host systems

An α-diimine compound (DC) bearing multiple hydroxyl and amine groups presents excellent self-assembly behavior, yielding DC self-assemblies with tunable morphologies ranging from solid spheres, nanotubes and capsulesviahydrogen bonds and π–π stacking interactions. These DC self-assemblies provide promising multifunctional hosts for varied metal species. As a typical example, Au nanoparticles are in situ generated and accommodated into both solid and hollow DC self-assemblies by one-pot and two-step fabrication processes, respectively, resulting in the formation of solid and hollow DC/Au hybrid nanostructures. Both solid and hollow DC self-assemblies also enable host Ni(II) ions to generate DC/Ni(II) catalysts for the efficient production of porous polyethylene (PE) beads consisting of numerous PE microspheres. Moreover, the yielded PE beads replicate the textural morphologies of the original DC/Ni(II) catalysts. These DC self-assemblies also might be further utilized to host varied metal species to fabricate versatile DC/metal nanoparticle (Ag, Pt, Pd, etc.) hybrids and porous polyolefin beads with desired morphologies.

Leaching- and fragmentation-free heterogenization of late transition metal complexes as a model system to prove the growth mechanism of polyethylene

Adopting a leaching- and fragmentation-free protocol, Ni(II) α-diimine complexes were covalently anchored on nonporous silica without any conventional tedious process. The supported catalysts polymerized ethylene with activities > 106 g-PE mol-Ni−1 h−1 bar−1 (10 kg-PE g-cat−1 at 5.5 bar pressure) when activated with a small amount (Al/Ni ∼100) of common aluminium alkyls (ethylaluminium sesquichloride, methylaluminium dichloride, and diethylaluminium chloride) in the absence of any methylaluminoxane. The polymer growth pattern from uniform spheres to fibers was clearly traced by using this model supported system, which depends on the catalytic activity, metal loading, and effective selection of co-catalysts. The polymerization results were compared with conventional porous silica supports immobilized by the same complex that undergoes fragmentation leading to a poor PE morphology.

Methylaluminum dichloride as a cocatalyst for Ni(II) α-diimine complexes catalyzed ethylene polymerization

Diimine Ni(II) catalysts have attained special interest due to their tunable polymerization activity and polymer microstructure by simple modification of the ligand architecture. 1,2 Technical process for olefin polymerization requires the use of suitable cocatalysts to transform inactive but readily prepared and handled catalyst precursors into the active species. The activity of methylaluminoxane (MAO) or its derivatives as cocatalysts is generally unmatched by other organoaluminum reagents. The ability of these substances to activate many kinds of catalytic precursors has been demonstrated for a wide range of transition metal catalyst precursors. However the practical use of MAO also poses some important drawbacks. For example, they are relatively expensive reagents that have to be used in large excess to achieve their optimum efficiency. Recently we have reported the polymerization/oligomerization behavior of late transition metal catalysts in combination with common alkyl aluminums like ethylaluminum sesquichloride (EAS). 3,4 In the present study we explore the use of methylaluminum dichloride (MADC) as a potential alternative for MAO towards the polymerization of ethylene with Ni(II) α-diimine catalysts.