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

Abstract

Polyethylene (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.

Controlling Polyethylene Molecular Weights and Distributions Using Chromium Complexes Supported by SNN-Tridentate Ligands

“…Therefore, the development of tunable catalytic systems that could produce different polyethylenes is highly desirable but challenging. , One of the industrially most relevant catalyst is the chromium-based Phillips catalyst (CrO x /SiO 2 ). − Discovered in 1951 by Hogan and Banks at Phillips Petroleum, this heterogeneous catalyst allows the manufacture of one-third of the high-density polyethylene (HDPE) commercialized, which is the most widely used polymer . Although the Phillips catalyst has been studied for over 70 years by both academic and industrial scientists, the nature of the initiation process, the coordination environment and the oxidation state of the metal in the active species, and the catalytic mechanism remain a hot and sometimes controversial topic. − Furthermore, much effort has been dedicated to the development of well-defined homogeneous Cr-based catalysts, ,− that are more amenable to detailed spectroscopic and structural studies than heterogeneous catalysts. In particular, multidentate ligands containing N, O, S, and/or P donor atoms have allowed a better control of the metal coordination sphere and a fine-tuning of its stereochemical features toward improved catalytic properties .…”

Influence of the N–H functionality on activating O,N,N-titanium complexes and controlling polyethylene molecular weights and distributions

“…8,9 Recently, polyethylenes with bimodal-distribution have attracted considerable attention because of their mechanical properties and processability. 10,11 Access to different classes of polyethylenes requires the use of specific metal-based catalysts, including heterogeneous Ziegler-Natta 12 and Phillips catalysts, 13 and homogeneous metallocene 14 and non-metallocene catalysts. 15 The latter, in particular, have spurred great interest in both academia and industry, [16][17][18][19][20][21][22] owing to their structural diversity and wide range of catalytic properties, including high activity, molecular weight control and mass distribution and for providing distinctive polymers that are difficult to produce using Ziegler-Natta and/or metallocene catalysts.…”

Fast Catalyst Ratio Estimate in Gas Phase Polyethylene Dual Catalyst System

“…It is well-known that both mechanical properties and processability of polyolefins can be improved by introducing bimodal characteristics or broadness in molecular weight distribution (MWD) or by changing chemical composition distribution (CCD). [2][3][4] Polyolefins with these broad distributions or bimodal distributions can be produced either by multiple reactors with different reaction conditions or by multiple types of catalytic sites in a single reactor, for example, a mixed catalyst system consisting of two catalysts. [2][3][4][5][6][7][8][9][10][11][12][13][14] The latter approach saves significant capital costs while enabling production of polymers with bimodal characteristics thanks to each catalyst in the mixed catalyst system producing polymer DOI: 10.1002/mren.202200029 with a different MWD and CCD.…”

“…[2][3][4] Polyolefins with these broad distributions or bimodal distributions can be produced either by multiple reactors with different reaction conditions or by multiple types of catalytic sites in a single reactor, for example, a mixed catalyst system consisting of two catalysts. [2][3][4][5][6][7][8][9][10][11][12][13][14] The latter approach saves significant capital costs while enabling production of polymers with bimodal characteristics thanks to each catalyst in the mixed catalyst system producing polymer DOI: 10.1002/mren.202200029 with a different MWD and CCD. In these single reactor, dual catalyst systems, the active catalyst ratio is a critical factor for determining the overall MWD and CCD of the produced products.…”