Thermostable α-Diimine Nickel(II) Catalyst for Ethylene Polymerization: Effects of the Substituted Backbone Structure on Catalytic Properties and Branching Structure of Polyethylene

Abstract

On the basis of the strategy of promoting thermostability of α-diimine nickel catalyst by ligand backbone framework, a series of α-diimine nickel(II) complexes with bulky camphyl or diaryl-substituted backbones, [2,6-(R2)2C6H3−NC(R1)−C(R1)N−2,6-(R2)2C6H3]NiBr2 (1a, R1 = Ph, R2 = CH3; 2a, R1 = 4-methylphenyl, R2 = CH3; 3a, R1 = 4-fluorophenyl, R2 = CH3; 4a, R1 = camphyl, R2 = CH3; 4b, R1 = camphyl, R2 = i-Pr), were synthesized and used as catalyst precursors for ethylene polymerization. Crystallographic analysis revealed that the bulky camphyl backbone has a valid steric-effect on the nickel center by blocking the axial site for the metal center and suppressing the potential rotation of the CAr−N bond. Ethylene polymerizations catalyzed by these nickel α-diimine complexes activated by MAO were systematically investigated and the influences of the substituted backbones as well as reaction temperature on the catalytic activity, molecular weight and branching structure of the polymers were evaluated. It was found that the catalysts containing a camphyl backbone have excellent thermal stability and polymer structure control for ethylene polymerizations. Even at 80 °C, the 4b/MAO system still kept high activity and relatively stable kinetics and produced high molecular weight polyethylene. Moreover, the branching degrees and branched chain distribution of the polyethylenes obtained by the complex could also be controlled by tuning the reaction temperature.

Recent advances in Ni-mediated ethylene chain growth: Nimine-donor ligand effects on catalytic activity, thermal stability and oligo-/polymer structure

“…2) [50,51]. In the presence of MAO, all these nickel complexes were active for ethylene polymerization.…”

Contaminant release from aged microplastic

“…In contrast to the other two polymer samples, one substance (2,4-dimethylaniline), a ligand of the polymerisation catalyst, [44] is released exclusively after thermo-oxidative exposure in the case of HDPE. As for the other two polymers, the IR spectra confirm the presence of compounds containing carbonyl groups after photooxidation.…”

The performance of methallyl nickel complexes and boron adducts in the catalytic activation of ethylene: a conceptual DFT perspective

“…A wide variety of nickel-based complexes are capable of polymerize and oligomerize ethylene [1][2][3][4][5][6]. The majority of them are cationic species formed by activation using different Lewis acids [1][2][3][4][5][6][7][8][9][10].…”

“…The majority of them are cationic species formed by activation using different Lewis acids [1][2][3][4][5][6][7][8][9][10]. Depending on the secondary ligand framework in a complex structure, it is possible to control molecular weight, polydispersity and branching of produced polyethylene [11][12][13].…”

“…Recently, we discovered a series of neutral methallyl nickel complexes (Scheme 2) able to polymerize or oligomerize ethylene using small amounts of co-activators such as B(C 6 F 5 ) 3 [22,23]. While analyzingthesenickel-basedcomplexesandtheiradducts,theimportance of the position of a special group or framework in a complex structurebecameclear.Infact,wefoundthatthereactivityofthesystems under study strongly depended on the position of the CN group and on the co-activator B(C 6 F 5 ) 3 coordinated to it.…”