Evaluation and Control of the Molar Mass Bimodality and Properties of Polyethylene from Novel Chromocene‐Based Dual Sites Catalysts

Abstract

AbstractPolyethylene (PE) with bimodal molecular weight distribution (MWD) has drawn attention from researchers because of its great processability and outstanding mechanical properties. Bimodal PE is successfully prepared by novel SiO2‐supported chromocene (S‐9)/chromium (CrOX) and chromocene (S‐9)/vanadium (V) dual sites catalysts in a single reactor. The molar mass bimodality, crystalline properties, and mechanical properties of the bimodal PE prepared by S‐9/CrOX catalysts are controllable through adjusting the loading of active centers. Those are also adjustable by using S‐9/V catalysts under the condition of adding 0.1 MPa hydrogen. Compared with CrOX/SiO2, 4CrOX4S9 shows an increase in tensile strength and Young's modulus by 38% and 17%, respectively. With the increase in high MW fraction, tensile strength, and Young's modulus both increase. S‐9/CrOX catalysts combining the advantages of two active centers show better tensile properties. S‐9/V catalysts have a similar trend in tensile properties. The complex viscosity, elastic modulus, and loss modulus increase with the growth in MW and the thickness of lamellae. Furthermore, the high and low MW fraction has good compatibility for both dual sites catalysts, and their resistance to slow crack growth is most likely to reach the standards for PE100 and PE100RC and even exceed.