Polyolefins metallocene catalysts

A long-standing goal in polyolefins is the synthesis of polymers bearing polar functional groups such as acrylate, esters, or vinyl ethers, etc [24,40]. These copolymers might endow polyolefins with useful properties such as adhesiveness, dyeability, paintability, and print-ibility. Advances have recently been made in polymerizing polar monomers with cationic metallocene catalysts... 

T. C. Chung, New utilities of metallocene catalysts and borane reagents in the functionalization and block/graft reactions of polyolefins, MetCon 95 Proceedings, USA, May 1995. 

Y.W. Park, Fulvene, metallocene catalysts and preparation method thereof, and preparation of polyolefines copoljmer using the same, US Patent No. 20050004385 A1 (2005). 

A characteristic of polyolefins synthesized with metallocene catalysts is their significantly lower polydispersity compared to one obtained by using heterogeneous Ziegler-Natta catalysts. Such narrower molecular mass distributions can lead to different mechanical properties of the resulting material. 

Group 4 metallocene catalysts are also applicable to the above sequential block co-polymerization method to furnish polyolefin and polar polymer block co-polymers. Frauenrath et al. and Chen and Jin " reported the synthesis of PE-/ -PMMA and PP-3-PMMA, respectively, using metallocene catalysts (e.g., raz--(C2H4)(Ind)2ZrMe2/ B(C5F5)3, iPP-/ -iPMMA PP segment 4/ = 8900, PDI= 1.90 block co-polymer 4/n = 10900, PDI = 1.66, MMA content = 17.1 mol%). 

The metallocene catalyst with cationic nature and spatially opened active site provides favorable condition for the incorporation of p-alkylstyrene (p-ms) to polyolefins. The p-ms groups can be easily metallated to produce "stable" polymeric anions for graft-from polymerization. With the coexist of anion-polymerizable monomers, we have prepared many graft copolymers, such as PE-g-PS, PE-g-PMMA, PE-g-PAN, PP-g-PS, PP-g-PB, PP-g-PI and PP-g-PMMA. 

The main benefits of metallocene catalysts in comparison to the conventional Ziegler-Natta catalysts are well-defined microstructures, high activity, narrow molar mass distribution and the possibility of tailor-made polyolefins. The advantages in metallocene catalyst chemistry offer a promising novel... 

A zirconium-based post-metallocene catalyst can produce PP-fo-PE. This has been reported as 13C NMR evidence of the real block nature for a polyolefin based materials [139]. 

Since the discovery of Ziegler-Natta catalysts, polyolefin industries have been developed mainly by using titanium-based catalysts. However, after the appearance of metallocene catalysts, much emphasis has been placed on those based on zirconium owing to the superiority of their performance over titano-cene catalysts. 

By using a (homogeneous) metallocene catalyst that is soluble in hydrocarbons, organic and inorganic particles (starches, cellulose, quartz grains, and metal powder) can be uniformly covered, and in the subsequent polymerization they can be coated with a film of polyolefins of variable thickness. 

Flowever, while no major breakthrough was made during the last ten years of the century in their traditional fields of endeavor, chemical corporations continued to improve the performance of their products by devising new methods for their manufacture. A case in point is supplied by the development of the metallocene catalysts. First described by Walter Kaminsky of the University of Hamburg in the 1980s and pioneered in the field of polyolefins by Exxon and Dow, these... 

Metallocene catalysts are the latest innovations to make a big impact in the polymer industry. They have been used mostly to make new polyolefin plastics, such as very-high-molecular-weight, bullet-proof polyethylene, but they have also been used to make elastomers. The catalysts make very regular stereospecific polymers similar to the Ziegler-Natta catalysts. 

The third advantage associated with metallocene catalysts is that the predominant mechanism for chain termination is by /3-hydride elimination. This produces a vinyl double bond at the end of each polymer chain. Further functionalization of the vinyl group by graft polymerization with maleic anhydride and other functional monomers is far more effective than is typical for polyolefins obtained by conventional catalysts. 

A major breakthrough in polymer production occurred with the discovery of metallocene catalysts [1]. We are now able to make polyolefins with a controlled level of branching (and tacticity). The simplest object is a statistically branched polymer, with a certain overall degree of polymerisation X, and a certain distance (monomer units) between successive branch points, which we shall call b. The basic goal of characterisation is to measure X and b from a minimum number of experiments in dilute solutions. 

POE and polyolefin plastomers (POP) are ethylene alpha olefin copolymers produced using constrained geometry and metallocene catalyst. They differ from traditional polyolefins in that they have narrow molecular weight distribution and a regular placement of the octene co-monomer on the ethylene backbone. This highly uniform distribution allows for some unique plastic characteristics. 

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