Achieving strictly linear polyethylenes by the NNN-Fe precatalysts finely tuned with different sizes of ortho-cycloalkyl substituents

Six examples of newly synthesized α,α’-bis (aryl)-2,3:5,6-bis (pentame thylene)pyridyliron complexes 2,3:5,6-{C₄H₈C(NAr)}₂C₅HN]FeCl₂ (Ar = 2-(c-C₅H₉)-6-MeC₆H₃ Fe1 , 2-(c-C₆H₁₁)-6-MeC₆H₃ Fe2 , 2-(c-C₈H₁₅)-6-MeC₆H₃ Fe3 , 2-(c-C₅H₉)-4,6-Me₂C₆H₂ Fe4 , 2-(c-C₆H₁₁)-4,6-Me₂C₆H₂ Fe5 , 2-(c-C₈H₁₅)-4,6-Me₂C₆H₂ Fe6 ; c refers as cyclic), on activation with methylalumoxane (MAO) or modified MAO (MMAO), exhibit high activities towards ethylene polymerization, producing strictly linear polyethylenes with terminal vinyl groups. The catalytic performances are systematically investigated along with various polymerization parameters as well as the microstructures of resultant polyethylenes. The steric hindrances of ortho-cycloalkyl substituents of N_imino-aryl groups significantly affect the activities of the corresponding iron precatalysts as well as the microstructures of resultant polyethylenes: higher steric hindrance the ortho-cycloalkyl substituents, higher activity the iron precatalyst, lower molecular weight the resultant polyethylenes. Experimental observations are additionally supported by the computational study. The resultant polyethylenes exhibited excellent hydrophobicity.