Selective distribution and contribution of nickel based pre-catalyst in the multisite catalyst for the synthesis of desirable bimodal polyethylene

Abstract

We report a selective immobilization strategy to control the catalytic performance of the target active species in hybrid multisite catalysts. The sterically bulky and electronically donated polyhedral oligomeric silsesquioxane (POSS) is introduced onto the support and offers extra immobilization sites for the target pre-catalyst. DFT and CO low-temperature adsorption facilitate to understand the distribution of active sites. The nickel pre-catalyst can interact with the POSS, endowing the scattered distribution of nickel sites. The large steric and electronic donated iron pre-catalyst exhibits the inertness to POSS, confining iron species on the POSS-free space. The selective dispersion of nickel species enhances its contribution in the synthesis of UHMWPE fraction with an exceptional activity, a much higher molecular weight and branching degree. This promoted contribution synchronously enhances the impact resistance (+27%), tensile strength (+53%), Young’s modulus (+111%) and elongation ratio (+37%) of the synthesized bimodal PE compared to those of commercial UHMWPE.