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As catalysts with a single active center, metallocene catalysts exhibit high catalytic activity. By altering the composition and structure of their ligands, it is possible to control properties such as the molecular weight distribution, stereoregularity, and degree of branching of the products, thereby providing more favorable conditions for the efficient production of polyolefins. The discovery of metallocene catalysts began in the early 1950s; Miller and Pauson, among others, first discovered metallocene—ferrocene in 1951. Subsequently, other metallocenes (chromocene, titanocene, zirconocene, and hafnocene) were synthesized for use in ethylene polymerization, but progress was slow and they did not receive sufficient attention. It was not until 1980 that Kaminsky and Sinn, among others, used a catalyst system composed of methylaluminoxane (MAO) and Cp2ZrMe2 (where Cp denotes cyclopentadiene and Me denotes methyl; the same applies hereafter) for the polymerization of ethylene, and discovered that this catalyst system exhibited very high activity, being dozens of times higher than that of the most active catalysts available at the time, which were based on MgCl2 as a carrier. It can be said that the discovery of MAO and the synthesis of new metallocene catalysts led to the emergence of a range of polymers with novel structures, such as isotactic polypropylene, highly syndiotactic polystyrene, and polyethylene with long-chain branching and a narrow relative molecular weight distribution. History of the development of metallocene catalysts: In 1973, Reichert and Meyer first discovered that adding a small amount of water to the Cp2TiEtCl/AlEtCl2 catalytic system not only did not deactivate the catalyst, but **also increased the activity of this system in catalyzing the polymerization of ethylene. Subsequently, Breslow et al. studied the effect of water on the catalytic system Cp2TiCl2/AlMe2Cl, which has low activity; they found that a small amount of water can partially hydrolyze AlMe2Cl to form the dialuminoxane ClMeAl-O-AlMeCl, which is a strong Lewis acid and facilitates the formation of methyl-substituted products Cp2TiMeCl with high activity in catalyzing the polymerization of ethylene. Meanwhile, Sinn and Kaminsky found that water causes partial hydrolysis of AlMe3 to form methaluminoxane (MAO), which plays a significant role in catalyzing the polymerization of olefins. In the presence of a certain amount of MAO, Cp2ZrMe2 or Cp2ZrCl2 can catalyze ethylene polymerization with very high activity. Subsequently, Kaminsky and others extended the homogeneous catalytic system composed of MAO and Cp2ZrCl2 to the polymerization of α-olefins such as propylene, and found that metallocene catalysts possessed catalytic activity. In 1982, Brintzinger and others synthesized chiral bridged metallocene compounds, marking the beginning of research on polyolefins with stereoregular properties at the molecular level. In 1984, John Ewen from ExxonMobil in the United States reported the production of isotactic and random copolymers of polypropylene using ansa-/MAO catalysts. Subsequently, Brintzinger and Kaminsky from the University of Konstanz jointly discovered the first catalyst for producing isotactic polypropylene. In 1985, Idemitsu Corporation (a Japanese company) was the first to produce syndiotactic polystyrene and filed a patent for it. In 1988, Ewen and others at Fina Company synthesized Cs-symmetric bridged cyclopentadienyl zirconium compounds containing fluorene rings; these metallocene catalysts provided two different sites for the insertion of propylene, and according to the mechanisms proposed by Brintzinger, Corradini, and Cossee, syndiotactic polypropylene could be obtained. Ewen et al. first synthesized high-purity syndiotactic polypropylene in high yield using an isopropyl carbon-bridged monofluorenyl monocyclopentadienyl zirconium dichloride/MAO catalytic system. This was also the first time in the world that pure syndiotactic polypropylene was obtained. Fina Company holds patents for metallocene catalysts, including patents for syndiotactic polypropylene. In 1989, Bercaw and others first synthesized compounds with a defined geometric structure. In 1990, the American company ExxonMobil obtained a patent for the monomethallic catalyst. Almost simultaneously, Dow also filed a patent for catalysts with constrained geometric configurations. Dow Corporation uses catalysts with its proprietary constrained geometry to catalyze olefin copolymerization, primarily for ethylene-octene copolymers and ethylene-styrene copolymers. In 1991, the American company ExxonMobil was the first to use Exxpol metallocene catalyst technology along with high-pressure ion polymerization to produce metallocene linear low-density polyethylene (mLLDPE) under the trade name Exact. Since then, large foreign companies have launched a wave of activity in the development and application of metallocene catalysts. In 1993, Razavi and Atwood synthesized diphenylmethane-bridged monofluorenyl monocyclopentadienyl zirconium dichloride, which could yield high-molecular-weight syndiotactic polypropylene. In 1995, Waymouth discovered bis((3-phenyl)indyl)zirconium dichloride for the synthesis of isotactic-random block copolypropylenes. In 2002, Atofina Petrochemicals achieved the first industrial production of metallocene polypropylene in Europe. The development history of metallocene catalysts in China: Research and development of metallocene catalysts and their catalytic products in China began in the late 1980s. The main institutions involved in this work include Sinopec Corporation, CNPC Corporation, the Institute of Chemistry of the Chinese Academy of Sciences, Zhejiang University, and East China University of Science and Technology. In 2002, the Beijing Research Institute of Chemical Technology successfully produced film-grade mLLDPE on an industrial gas-phase polyethylene plant owned by Qilu Petrochemical Company, thereby becoming the first to implement the industrial use of metallocene catalysts. In 2007, the Daqing Petrochemical Branch of Sinopec introduced the proprietary metallocene catalyst technology from the American company Univation, and began producing more than 3,000 tons of film-grade mPE, which was then brought to market. In 2011, the metallocene catalyst developed by the Beijing Research Institute of Petrochemicals of Sinopec was successfully put into industrial use, enabling the mass production of film material and heat-resistant polyethylene (PE-RT) pipe material at Sinopec’s Qilu Branch’s gas-phase polyethylene production facility. In 2012, the metallocene catalyst developed by the China Petroleum and Chemical Research Institute operated continuously for 276 hours in a polyethylene pilot plant, producing a total of 6.5 tons of pilot-scale product. In 2018, Yanshan Petrochemical successfully produced metallocene polypropylene products. This represents the first successful development of metallocene polypropylene using continuous production facilities in our country, marking Yanshan Petrochemical as the first domestic manufacturer of metallocene polypropylene on a continuous basis. In 2020, significant breakthroughs were achieved in the industrial-scale testing of the metallocene polypropylene catalysts independently developed by the Beijing Research Institute of Chemical Technology, and two types of metallocene ultra-high melt mass flow rate polypropylene (mUHMIPP) were developed. In 2022, the metallocene polypropylene catalyst developed independently by the Beijing Research Institute of Chemical Technology was successfully used for the first time on an industrial scale in the loop polypropylene production facility of Zhongyuan Petrochemical, enabling the production of high-performance homopolymer and random copolymer metallocene polypropylene resins. In recent years, the production of polyolefin products manufactured using metallocene catalysts has increased rapidly, and these products have captured a share of the market thanks to their excellent material properties. Specifically, metallocene polyolefin products include metallocene polyethylene (mPE), metallocene polypropylene (mPP), metallocene syndiotactic styrene, metallocene cycloolefins, polyolefin elastomers (POE), and cycloolefin copolymers (COC/COP), among others.