Ethylene polymerization by the chromium catalysts based on bidentate [O, PO] or [S, P] ligands

Abstract

Novel chromium catalysts based on bidentate phenoxy‐phosphinoyl (HO‐2R1‐4R2‐6(Ph2PO)C6H2: R1 = R2 = H, 3a; R1 = tBu, R2 = H, 3b; R1 = R2 = tBu, 3c; R1 = R2 = cumyl, 3d; R1 = anthracenyl, R2 = H, 3e) and thiophenol‐phosphine (HS‐2R1‐4R2‐6(Ph2P)C6H2: R1 = R2 = H, 4a; R1 = SiMe3, R2 = H, 4b) were prepared and characterized. Treatment with modified methyaluminoxane, these catalysts displayed moderate to high‐catalytic activities for ethylene polymerization. The activities of them were higher than those of the corresponding catalysts based on bidentate phenoxy‐phosphine ligands. Both the coordinated donors and the ortho‐substituent of the ligands played an important role in improving catalytic activity. The effects of reaction parameters, such as cocatalyst and Al/Cr molar ratio as well as reaction temperature, on ethylene polymerization behaviors were investigated in detail for two favorable catalytic systems, 3b/CrCl3(thf)3 and 4b/CrCl3(thf)3. Catalyst 4b/CrCl3(thf)3 displayed higher catalytic activity and better temperature tolerance for ethylene polymerization than 3b/CrCl3(thf)3. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 311–319, 2010

Further studies on the effects of substituents at the Cp and salicyladiminato ligands of half-sandwich chromium(III) complexes on their catalytic properties for ethylene polymerization

“…The high melting transition temperature implies the obtained polyethylenes are linear, and the sharp melting peak is indicative of that the molecular weight distribution of these polyethylenes is narrow. 13 C NMR spectra of the polyethylene samples obtained at 130 C in C 6 D 4 Cl 2 show no signals for branches [35,36], which confirms the linear structure of the polyethylenes.…”

“…The OeCreCl and NeCreCl bond angles of complexes 1e3 change in the ranges of 92.05(5)e94.90 (13) and 96.90(13)-101.34 (8) , respectively, with the variation in R 1 and R 2 groups. For complexes with a bulkier R 1 and a less bulky R 2 , the OeCreCl bond angle would be larger (2 > 3) and the NeCreCl bond angle would be smaller (3 > 2).…”

“…The chromium-based heterogeneous catalysts of Phillips and Union Carbide systems (Cr/SiO 2 ) have been commercially applied in the production of high density polyethylene for long time [9] and many research efforts have been devoted to the studies on structurally well-defined homogeneous single-site Cr complexes as model systems of the chromium-based heterogeneous catalysts. So far, a large number of non-metallocene chromium(III) complexes [7,10,11] have been reported to show relatively high catalytic activity for ethylene polymerization upon activation with alkylaluminum or alkylaluminum chlorides compared to the MAOactivated systems [12,13]. Some half-metallocene chromium(III) complexes, such as Cp*Cr(acac)Cl [14], Cp*Cr(C 6 F 5 ) (s 3 -Bn) (Bn ¼ benzyl) [15], and half-metallocene chromium(III) complexes Cp*CrLCl bearing a b-ketoiminato, b-diketiminate [16], hydroxyindanimine [17], or salicylaldiminato ligand [18e20], have also been reported to exhibit moderate to high catalytic activity for ethylene polymerization when activated with alkylaluminum.…”

Novel vanadium(III) complexes with tridentate phenoxy‐phosphine [O,P(O),O] ligands: Synthesis, characterization, and catalytic behavior of ethylene polymerization and copolymerization with 10‐undecen‐1‐ol

“…Increasing ligands denticity seems to be an efficient method to stabilize the active species of vanadium catalyst, which produced high‐molecular‐weight polymers with high catalytic activities 21–33. Introducing some softer second‐row donors in the ligand is another effective method to offer beneficial stabilization of the highly reactive metal center 34–41. The combination of hard donors with soft phosphine donors in early transition metal polymerization catalysis increased the configurational stability of the catalyst, which was found by Gibson34–36 and Tang 42–49.…”

Controllable Synthesis of Multiarm Star‐Shaped Copolymers Composed of Phosphoester Chains and Their Application on Drug Delivery

“…[23,24] In addition, their backbones are recognizable to enzymes (e.g., alkaline phosphatase) and can be cleaved or built up under physiological conditions. [25][26][27] For instance, Wooley and co-workers have done lots of research on the preparation of multifunctional linear phosphoester block copolymer. They introduced vinyls and acetenyls in the side chain segments and developed four types of micelles with different surface charges by postmodification, which can be used for drug delivery and gene therapy.…”