One of the biggest challenges of modern organometallic chemistry is its application to new technologies and materials. For this purpose, many types of complexes are synthesized by people, modified, and then applied to new catalytic processes, whileMetallocene complexesNothing less than one of the hottest areas in this regard. The field of catalytic olefin polymerization was established in the fifties of the twentieth century by Ziegler Natta and Phillips catalysts, and the emergence of metallocene catalysts has sparked a revival in the field of catalytic olefin polymerization in the last two or three decades.
The reason why metallocene catalysts are favored by the majority of scientists is because of their olefin polymerizationUnique performanceToday, let's take a look at the characteristics of metallocene catalysts.
The catalytic activity is high
Metallocene catalysts are:Homogeneous catalysts, every molecule of its active center is dissolved in the solvent, so its activity is higher. Its activity can reach hundreds or even thousands of times the activity of traditional Ziegler Natta and Phillips catalysts. For example, at 70, the bisfluorene zirconium complex containing 1 gram of zirconium (C13H8-C2H4-C13H8) ZRCL2 can produce 3 10 5kg of polyethylene under the activation of the cocatalyst, such a high catalytic activity can greatly reduce the amount of catalyst used in industrial production, and the ash content of such a small catalyst is allowed to remain in the polyolefin product.
Single active center
Metallocene catalysts belong to homogeneous catalysts, also known asSingle site catalysts, with a single catalytically active center. As an olefin catalyst, since its catalytically active center is in a restricted coordination environment, only monomers are allowed to coordinate to the active site of the catalyst and therefore canPrecise controlThe molecular weight of the polymer, the molecular weight distribution, the content of the comonomer and the distribution of the sequence of its polymer fragments on the main polymer chain, etc. The molecular weight distribution of polymers catalyzed by metallocene catalysts (mw mn2) is narrower than that of polymers prepared by polycentric catalysts (mw mn=3, 8). Moreover, the distribution of comonomers in the polymer backbone is also relatively uniform, and the long and short branches are regularly distributed in the main polymer chain, which determines that the new polymer materials have new applications (such as MLLDPE), and then expand the market prospects.
It can effectively regulate the microstructure of polymers
By modifying the electronic effects and spatial structure of cyclopentadienyl (CP)-containing ligands, many metallocene complexes with different structural types can be designed and synthesized. This modification can greatly alter the catalytic activity of the catalyst and also affect some of the performance parameters of the resulting polymer, such as molecular weight and comonomer content. Not only that, metallocene catalysts with some symmetry factors can also achieve stereoselective control of olefin polymerization reactions, and generate polyolefin materials with certain stereoselectivity for latent olefin polymerization, such as: fully isostatic polypropylene, metaisostatic polypropylene, random polypropylene, semi-isometric polypropylene, vertical block polypropylene, interstructured polystyrene, etc. Polyolefins can be manufactured with a specific degree of stereoregularity to exhibit unique properties that allow them to be adapted to a wide range of applications. Therefore, by controlling the polymerization conditions and modifying the molecular structure of the catalyst, it is easy to obtain polymers with suitable market needs for various markets.
Excellent copolymerization properties
Metallocene catalysts can catalyze the copolymerization of ethylene with many comonomers, and more than 50 comonomers have been reported so far. It has also been found that in addition to the common -olefins, norbornene, and styrene, the monomers that can be copolymerized can also be conjugated diolefins and polar monomers. Therefore, metallocene catalysts can produce a variety of new polyolefin products, such a wide variety of varieties and excellent performance, can be widely used in all fields of production and life.
onArticle: [Non-*** catalyst is used in VOCs catalytic oxidation process].