•Ni(II) and Pd(II) complexes with P atom in the side arm were successfully synthesized.•All the complexes were highly active for norbornene polymerization.•The side arm of a P donor have a strong influence on catalytic activity.A series of nickel (II) complexes (1a-4a) and palladium (II) complexes (1b-4b) bearing N,N,P tridentate ligands derived from amino-alkyl phosphines and 2-pyridinecarboxaldehyde and 2-quinolinecarboxaldehyde were synthesized and characterized. X-ray diffraction analysis revealed that complexes 1a, 4a, and 2b adopted square-pyramidal geometry, trigonal bipyramid, and distorted square-planar geometry, respectively. Activated by methylaluminoxane (MAO), all the complexes were highly active for norbornene polymerization in a vinyl addition fashion, affording high molecular weight polymers with narrow molecular weight distributions. The activities of palladium complexes are particularly notable; the highest activity reached 2.45 × 108 g PNB (mol of Ni)−1 h−1. The activities of the complexes were affected by the ligand structure as well as the reaction parameters such as polymerization temperature, time, and cocatalyst loading.Download high-res image (114KB)Download full-size image

Half-titanocene complexes bearing dibenzhydryl-substituted aryloxide ligands (2a−2d) were prepared. Among them, 2c adopted a three-legged distorted tetrahedral geometry evidenced by X-ray crystallography. The poly-1,3-butadiene with high molecular weight and narrow molecular weight distribution was obtained by using these complexes as the catalysts activated with methylaluminoxane (MAO). The catalytic activities of the complexes depended on their structures. The Ti―O―C bond in the complexes with large angle afforded them with higher activity, while Cp*-based complexes exhibited lower activities than the Cp-based analogues. The activity of complex increased with increasing the polymerization temperature while the selectivity remained no change, indicating the high thermal stability. Furthermore, the polymerization of 1,3-butadiene catalyzed by 2a/MAO at 0 °C has been found in a living fashion.

ABSTRACTIn this work, an octadecylamine-modified graphene oxide (ODA-GO)-MgCl-supported Ziegler–Natta catalyst was synthesized by reacting ODA-GO with a Grignard reagent, followed by anchoring TiCl4 to the structure. The effect of the ODA-GO on the catalyst morphology and ethylene polymerization behavior was examined. The resultant polyethylene (PE)/ODA-GO nanocomposites directly mirrored the catalyst morphology by forming a layered morphology, and the ODA-GO fillers were well dispersed in the PE matrix and showed strong interfacial adhesion with it. The resultant PE/ODA-GO nanocomposites exhibited better thermal stability and mechanical properties than neat PE, even with a small amount of ODA-GO added. Thus, this work provides a facile approach to the production of high-performance PE. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 855–860

•Effect of alkylaluminum cocatalyst in Nd-based ternary catalyst was studied.•Isoprene polymerization results based on four catalyst systems shown different for the kind of alkylaluminum.•Local structures around Nd center of the four catalysts were obtained by XAFS technique.•The structural information is beneficial to elucidate the effect of alkylaluminum to the isoprene polymerization.Nd-based ternary catalyst systems are widely used for rubber industry. The effect of alkylaluminum cocatalysts has been investigated for decades. However, there is a lack of structural evidence, especially the quantitative result to illustrate the inner reasons. In the present paper, the effect of different alkylaluminum cocatalysts to the polymerization performance of isoprene has been studied. Catalysts adopted in the present paper all show high 1,4-cis selectivity (above 96%) of polyisoprene and kind of alkylaluminum is not the crucial factor to affect the microstructure of polyisoprene. By comparing the polymerization performance of isoprene and the local atomic structure around Nd centers, it can be concluded that the short carbon-chain in the alkylaluminum cocatalyst is helpful to increase the percent conversion of isoprene. While the carbon-chain length and number in each alkylaluminum cocatalyst can be used to modulate the molecular weight of the synthesized polyisoprene. All the results in the present paper provide a clue to improve the Nd-based ternary catalyst for rubber synthesis.Download high-res image (242KB)Download full-size image

Nd-based ternary catalysts are widely used for the polymerization of isoprene in rubber industry, however structure information during the polymerization of isoprene as well as the catalytic mechanism are still ambiguous. In this paper, the in situ XAFS technique was used to extract the local atomic structure around the Nd center of the catalyst consisting of Nd(vers)3, AlEt3, and Al(iBu)2Cl. Theoretical calculations were used to verify the structure changes in the alkylation process. Four catalysts with different alkylaluminums {AlEt3, Al(nOct)3, Al(iBu)3, and Al(iBu)2H} were, respectively, used for the polymerization of isoprene. The results demonstrate that the substitution of Nd–C for Nd–O bonds is reasonable in the alkylation step. The structural evolutions in the alkylation and chlorination steps, as well as in the polymerization processes of isoprene are all similar for these Nd-based ternary catalysts with different alkylaluminum components. In the polymerization process of isoprene, there are only about 2 Nd–Cl bonds at 2.85 Å and 1–2 Nd–C bonds at 2.42 Å around the Nd centers which are in a monomer state. The Nd–C bonds can be attributed to the contribution of isoprene. This highly-opened structure of the Nd active centers activates greatly the catalytic activity of the Nd-based ternary catalysts. A conjectural catalytic mechanism for the polymerization of isoprene has been deciphered on the basis of the in situ XAFS results. This study is expected to be helpful for the improvement and application of the Nd-based ternary catalysts.

We demonstrated here the crosslinked N-doped graphene (NG) can be rapidly prepared through a one-step burning process of graphene oxide. The doping process completed within 3 minutes and the N content in the obtained NG reached to 5.6%. The obtained crosslinked NG shows mesoporous structure with relatively high specific area, large pore volume and various N types. As a supercapacitor, the resultant NG exhibits rapid diffusion of electrolyte ions and shows superior capacitive performance, excellent specific capacitance (317.5 F/g at the current density of 1 A/g) and high cycling stability (93% retention after 5000 cycles). The obtained results indicate that the crosslinked NG is a promising candidate for creating supercapacitors with high performance and relatively low cost.

In this study, a spherical grapheme (G)/MgCl2-supported Ti-based Ziegler-Natta catalyst was prepared by a facile spray-coagglomeration method. The effects of graphene on catalyst morphology, ethylene polymerization behavior, and polymer properties were investigated. The resultant product was spherical, and the G was well dispersed in the whole polyethylene (PE) matrix. In addition, the thermal stability and mechanical properties of PE were significantly enhanced with the introduction of a very small amount of G (0.09 wt%) due to good dispersion of the graphene fillers in the PE matrix. Thus, this work provides a facile approach for the production of high-performance PE.

A novel exfoliated-MoS2 (EMoS2)–MgCl bi-supported Ziegler-Natta catalyst was synthesized by the reaction of Grignard reagent and EMoS2, followed by anchoring with TiCl4. The tendency of the individual EMoS2 layers to aggregate was prevented by covering them with solid-state Ziegler-Natta catalyst. The resultant catalyst was applied to ethylene polymerization, forming polyethylene (PE)/EMoS2 organic-inorganic hybrid nanocomposites. The resultant products had a flake-shape morphology, with EMoS2 well dispersed in the PE matrix. In addition, the thermal stability and mechanical properties of PE were significantly enhanced by the introduction of EMoS2.

In the present article, an efficient and thermally stable vanadium (V)-based Ziegler–Natta catalyst supported on graphene oxide (GO) was synthesized. The resultant catalyst exhibited highly dispersed active sites along the surface, superior catalytic activity toward ethylene polymerization, and enhanced thermal stability, in contrast to the conventional VOCl3 catalyst. Interestingly, the resultant polyethylene (PE)/GO nanocomposite exhibited a higher thermal stability and better mechanical properties than PE obtained using VOCl3. Transmission electron microscopy reveals graphene homogeneously dispersed within the PE matrix.

Three pyridinyl based compounds, diphenylpyridin-2-yl phosphate (DPPyP), phenyldipyridin-2-yl phosphate (PDPyP), and tripyridin-2-yl phosphate (TPyP), were designed, synthesized, and applied in an iron catalyst as donors for 1,2-stereopolymerization of 1,3-butadiene in hexane. In combination with AliBu3, the DPPyP assisted iron catalyst is capable of 1,2-syndiotactic polymerization (1,2-selectivity, syndiotacticity) of 1,3-butadiene with high activity reaching 258 480 kg(polymer)/mol(Fe)·h at a butadiene/Fe feeding ratio of 8000 at 50 °C. The 1,2-regioselectivity, activity, and the morphology of resultant polymers can be controlled by the donor structures. The thermal stability of the catalysts were significant because a remarkably enhanced activity was observed while the high 1,2-stereoselectivity was unaltered in the range 50–80 °C. This work enabled us to have access to a highly active, 1,2-syndiotactic and thermally robust catalyst with ease of catalyst preparation, which could match the availability in industrial application for 1,2-syndiotactic polybutadiene.

•Magnetic properties of a series of four pentacoordinate Co(II) complexes were evaluated.•The compounds exhibited a field induced slow relaxation of magnetisation.•The compounds showed the uniaxial type of magnetic anisotropy.•D parameters are 45.8 cm−1 (1), 38.4 cm−1 (2), −43.9 cm−1 (3) and −41.3 cm−1 (4).•In the cases of complexes 1–3, a very large rhombicity was revealed (E/D = from 0.24 to 0.31).Static and dynamic magnetic properties of a series of four pentacoordinate [CoII(L3A-D)Cl2] complexes 1–4 (1, L3A = N,N′-bis(2,4,6-trimethylphenyl)pyridine-2,6-dicarboximidoyl dichloride; 2, L3B = N,N′-bis(2,6-dimethylphenyl)pyridine-2,6-dicarboximidoyl dichloride; 3, L3C = N,N′-bis(4-chloro-2,6-dimethylphenyl)pyridine-2,6-dicarboximidoyl dichloride; and 4, L3D = N,N′-bis(2,6-diisopropyl)pyridine-2,6-dicarboximidoyl dichloride) were thoroughly studied. Irrespective of the sign of the zero-field splitting parameter D, all the compounds 1–4 showed the uniaxial type of magnetic anisotropy and also slow relaxation of magnetization, hence belong to the class of field-induced single-ion magnets. The values of the D parameter range from large and positive in 1 and 2 (45.8 cm−1, and 38.4 cm−1, respectively) to large and negative in 3 and 4 (−43.9 cm−1, and −41.3 cm−1, respectively). In the cases of complexes 1–3, a very large rhombicity was revealed (E/D = from 0.24 to 0.31). Only in compound 4, which possesses large negative axial and practically zero rhombic magnetic anisotropy (D = −41.3 cm−1, E/D = 0.0), the extraction of spin reversal barrier, U = 22.8 K, from Argand diagram was feasible. The experimental findings were also supported by ab initio multi-reference CASSCF/NEVPT2 calculations. Finally, the magneto-structural correlation of D vs. τ was proposed, showing that the square-pyramidal Co(II) complexes adopt large and negative D values, and moreover, that the sign of D is changed to positive on transition to the chromophore geometries closer to the trigonal bipyramidal arrangement, with a crossing point at τ ≈ 0.29.The magnetic properties of a series of four pentacoordinate Co(II) complexes were thoroughly evaluated. It has been revealed that all the compounds exhibited indications of field induced slow relaxation of magnetisation.

•The catalyst has high 1,2-syndiotactic selectivity in 1,3-butadiene polymerization.•The catalyst shows remarkable thermal stability in the range of 50–100 °C.•The catalyst has potential application in industry production of 1,2-polybutadiene.A novel class of organic phosphates were synthesized and applied in iron catalyst as additive for 1,2-syndiotactic polymerization of 1,3-butadiene in combination with aluminum alkyls (Ali−Bu3 or AlEt3) in hexane at industrial favorable 50–100 °C. Remarkable enhanced polymer productivity (up to 486 kg (polymer)/mol(Fe) h) and excellent 1,2-syndiotactic regularity have been achieved at 50–100 °C in all examing cases. All the polymers obtained under various polymerization conditions possess prevailingly 1,2 inserted homo-sequences up to 94.7% 1,2-selectivity in syndiotactic arrangements (up to 94.4%, denoted by rrrr) with melting point ranging from 170 to 182 °C. The current in-situ generated catalyst systems feature high productivity, selectivity, robustness (e.g. high thermal stability, good tolerance to poisons and environmentally friendly hexane as solution polymerization medium) and single-site behaviour. These all extend the practical usefulness of these versatile phosphates assisted catalyst, and they are promising candidates to act as ancillary additive for industrial applicable 1,2-syndiotactic polymerization of 1,3-butadiene.

Cobalt and nickel complexes (1a-1d and 2a-2d, respectively) supported by 2-imidate-pyridine ligands were synthesized and used for 1,3-butadiene polymerization. The complexes were characterized by IR and element analysis, and complex 1a was further characterized by single-crystal X-ray diffraction. The solid state structure of complex 1a displayed a distorted tetrahedral geometry. Upon activation with ethylaluminum sesquichloride (EASC), all the complexes showed high activities toward 1,3-butadiene polymerization. The cobalt complexes produced polymers with high cis-1,4 contents and high molecular weights, while the nickel complexes displayed low cis-1,4 selectivity and the resulting polymers had low molecular weights. The catalytic activities of the complexes highly depended on the ligand structure. With the increment of polymerization temperature, the cis-1,4 content and the molecular weight of the resulting polymer decreased.

trans-1,4-Selective coordination chain transfer polymerization of 1,3-butadiene was achieved by using a Nd(Oi-Pr)3/Mg(n-Bu)2 catalyst, affording polybutadienes having high trans-1,4 contents (ca. 96%), moderate molecular weight (Mn = 1.0–2.3 × 104), and narrow polydispersity (Mw/Mn ∼ 1.7). In the system, Mg(n-Bu)2 acted as both a co-catalyst and a chain transfer agent, and the calculated transfer efficiencies of Mg(n-Bu)2 were 27–34%. The produced living polybutadiene could further initiate the ring-opening polymerization of ε-CL/lactide to give TPB-b-PCL/PLA copolymers in a controlled fashion. The crystalline amphiphilic copolymers (TPB-b-PCL/PLA) were subsequently applied to investigate their self-assembly behavior by adding a selective solvent into a polymer/co-solvent solution. The polymer plates composed of a crystallized TPB core and PCL/PLA brushes were obtained by the crystallization-driven self-assembly. Moreover, the morphology of the polymers underwent change from nano-sized plates to micro-sized plates with increasing addition of the selective solvent.

Lanthanide-based catalysts are highly active for isoprene polymerization in hexane. In this paper, a ternary catalyst consisting of neodymium neodecanoate {Nd(vers)3}, Al(iBu)3 and Al(iBu)2Cl was studied by using X-ray-absorption fine-structure (XAFS) technique. A sealed and moisture-proof liquid sample cell with adjustable thickness was designed for Nd LIII-edge XAFS measurements. Based on the XAFS data analysis, detailed structure changes around the Nd center were obtained. It was found that the Nd(vers)3 molecules formed an oligomer structure in hexane solution with two Nd–O subshells (5O @ 2.39 Å and 5O @ 2.54 Å) around the Nd center. The alkylation process by adding Al(iBu)3 to the hexane solution of Nd(vers)3 partially destroyed the aggregation degree of Nd(vers)3 molecules in hexane solution. Al(iBu)3 ligands were bonded to the Nd center by Nd–C bonding. With the Nd:Al ratio increasing from 1:2.5 to 1:10, the O neighbors around Nd decreased from 4 to 2 but with an unchanged Nd–O bond length of 2.38 Å, and the C neighbors around Nd were kept at ca. 4 with Nd–C bond lengths in the range of 2.57–2.58 Å. The Nd–O bonds can be further replaced by Nd–C bonds during the aging process. The chlorination process by adding Al(iBu)2Cl to the mixture solution of Nd(vers)3 and Al(iBu)3 restrained intensively the agglomeration of Nd(vers)3 molecules in hexane solution. Al(iBu)2Cl ligands were bonded to the Nd center by Nd–Cl bonds. There were about 3–4 C neighbors at 2.58 Å, 2 Cl neighbors at 2.87 Å, and 2 Al next-neighbors at 3.14 Å around the Nd center. After allowing the ternary catalyst to stand for 5 days, the coordination numbers of Nd–C and Nd–Cl were all stabilized to 3 without bond length changes, and partial single Cl− anions were also bonded to the Nd center. All these structural details and their change tendency demonstrate that the decrease of aggregation degree of Nd(vers)3 molecules in hexane solution can improve the catalytic activity of the ternary lanthanide-based catalyst system.

•Co(II) complexes bearing bidentate oxazoline-containing ligands were synthesized.•The complexes displayed high activity for 1,3-butadiene polymerization.•The addition of PPh3 could switch the selectivity from cis-1,4 to 1,2-manner.A series of cobalt complexes supported by pyridine–oxazoline (Pyox) and quinoline–oxazoline (Quox) were synthesized. Determined by single crystal X-ray crystallography, complexes 6a and 7c adopted distorted octahedron and trigonal bipyramid geometries, respectively, while complex 6b existed as an ion pair comprised of [CoL2]2+ and [CoCl4]2−, in which the cationic and anionic moieties displayed distorted octahedron and tetrahedral geometries, respectively. Upon activation with ethylaluminium sesquichloride (EASC), these cobalt complexes exhibited high catalytic activity and cis-1,4-selectivity toward 1,3-butadiene polymerization. The selectivity of the catalytic system could be switched from cis-1,4 to 1,2-fashion via the addition of PPh3. The effects of ligand environment, polymerization temperature, and [Al]/[Co] ratio on the polymerization were investigated in detail.Cobalt complexes supported by pyridine–oxazoline (Pyox) and quinoline–oxazoline (Quox) were synthesized and polymerized 1,3-butadiene to give polymers with high cis-1,4 contents. The selectivity of the catalytic system could be switched from cis-1,4 to 1,2-fashion via the addition of PPh3.

•Co(II) and Ni(II) complexes performed high activities to butadiene polymerization.•Ligand environment and polymerization conditions influenced catalytic behaviors.•Addition of PPh3 to Co(II) system resulted in 1,2-polybutadiene.A series of 2,6-bis(imidate)pyridine ligated Co(II) and Ni(II) complexes with general formula of [2,6-(2,6-iPr2C6H3N = COR)2C5H3N]MX2 (R = Me, M = Co, X = Cl (1a); R = Me, M = Ni, X = Br (2a); R = Et, M = Co, X = Cl (1b); R = Et, M = Ni, X = Br (2b); R = iPr, M = Co, X = Cl (1c); R = iPr, M = Ni, X = Br (2c); R = CH2CF3, M = Co, X = Cl (1d); R = CH2CF3, M = Ni, X = Br (2d); R = Ph, M = Co, X = Cl (1e); R = Ph, M = Ni, X = Br (2e); R = CH2Ph, M = Co, X = Cl (1f); R = CH2Ph, M = Ni, X = Br (2f)) were synthesized. Determined by single crystal X-ray analysis, complexes 1e and 2c with NNN tridentate ligands adopted approximate distorted square pyramidal configurations whereas complex 1f with tridentate NNO ligand displayed a distorted square pyramidal configuration. Activated by methylaluminoxane (MAO), these complexes exhibited high cis-1,4 selectivity towards 1,3-butadiene polymerization. The structure of substituent and polymerization conditions significantly influenced the catalytic behaviors of the complexes. The addition of PPh3 to the Co(II)-based systems enhanced the catalytic activity and switched the selectivity from cis-1,4 to 1,2 manner.A series of 2,6-bis(imidate)pyridine Co(II) and Ni(II) complexes had been synthesized and performed high activities and high cis-1,4 selectivities towards 1,3-butadiene polymerization. The ligand environment and polymerization conditions significantly influenced the catalytic behaviors of the corresponding complexes. Addition of PPh3 to the Co(II)-based systems increased their catalytic activities and also switched the selectivity from cis-1,4 to 1,2 manner.

•Co(II) complexes bearing pyridine bisoxazoline ligands were successfully synthesized.•The complexes displayed high activity, cis-1,4 selectivity, and thermostability for 1,3-butadiene polymerization.•The addition of PPh3 could switch the selectivity from cis-1,4 to 1,2-manner.A series of ion-pair cobalt complexes bearing pyridine bisoxazoline ligands were successfully synthesized and characterized by IR spectroscopy and elemental analysis. Determined by X-ray crystallographic analysis, complexes 4a, 4b, 4e, and 4f existed as ion pairs comprised of [CoL2]2+ and [CoCl4]2−. In the complex, the cobalt atom was coordinated by six nitrogen atoms from two ligands, and its coordination geometry at the cobalt center of [CoL2]2+ can be described as distorted octahedron. In combination with ethylaluminum sesquichloride, these cobalt complexes displayed high catalytic activity and cis-1,4-selectivity towards 1,3-butadiene polymerization. The selectivity of the catalytic system can be tuned to predominantly 1,2-fashion via addition of PPh3. The effects of reaction parameters and the ligand environment on the polymerization were also investigated.Figure optionsDownload full-size imageDownload as PowerPoint slide

•All three CoCl2 complexes performed high activities towards butadiene polymerization.•Addition of PPh3 or PO(OPh)3 cause distinctly different polymerization behaviors.•ONO, ONN Co(II) complexes displayed obvious chain transfer towards ZnEt2.Three kinds of ONO (a), ONN (b), and NNN (c) tridentate Co(II) complexes were synthesized and thoroughly characterized. Determined by single crystal X-ray analysis, the solid structures of b and c displayed distorted trigonal bipyramidal and square pyramidal geometries around the metal centre, respectively. In combination with methylaluminoxane (MAO), all three complexes exhibited high catalytic activities towards 1,3-butadiene polymerization, affording polymers with predominant cis-1,4-contents. With addition of PPh3 into the polymerization system, polybutadienes having predominant 1,2-contents were obtained, while the addition of PO(OPh)3 showed little influence on the microstructure of the polymer. In the investigation of chain transfer polymerization of 1,3-butadiene at the presence of ZnEt2, for complexes a and b, monotonous decreasing in molecular weight along with and an increasing of cis-1,4-content were obtained with an increasing molar ratio of Zn/Co, for complex c, however, unconspicuous changes was observed.Graphical abstractThree kinds of CoCl2-based complexes had been synthesized and all of them performed high activity and high cis-1,4-selectivity towards 1,3-butadiene polymerization. Addition PO(OPh)3 showed no influence to the microstructure of the resulting polybutadiene, albeit addition of PPh3 resulted in 1,2-enriched structure. ONO, ONN CoCl2 complexes displayed obvious chain transfer towards ZnEt2, monotonous decreasing in molecular weight along with and an increasing of cis-1,4-content were observed.

•Co(II), Ni(II), and Fe(II) complexes bearing quinolinylimidoylchloride ligands.•Three complexes performed distinctly different butadiene polymerization behavior.•Imidoylchloride Co(II) and Ni(II) complexes displayed relative higher activities.A series of Co(II), Ni(II), and Fe(II) complexes supported by quinolinylimidoylchloride ligands [2-(N-ArN = CCl)C9H6N]MtBr2 (Ar = 2,6-iPr2C6H3, M = Co (1a), Mt = Ni (2a), Mt = Fe (3a); Ar = 2,6-Et2C6H3, Mt = Co (1b), Mt = Ni (2b), Mt = Fe (3b); Ar = 2,6-Me2C6H3, Mt = Co (1c), Mt = Ni (2c), Mt = Fe (3c); Ar = C6H5, Mt = Co (1d), Mt = Ni (2d), Mt = Fe (3d); Ar = 4-ClC6H4, Mt = Co (1e), Mt = Ni (2e), Mt = Fe (3e); Ar = 4-OMe-C6H4, Mt = Co (1f), Mt = Ni (2f), Mt = Fe (3f)) were synthesized. The solid structure of ligand c, complexes 1e and 2a were characterized by single crystal X-ray analysis, showing that 1e was tetra-coordinate with a distorted tetrahedral geometry and 2a was penta-coordinate with a distorted trigonal bipyramid configuration. The imidoylchloride Co(II) and Ni(II) complexes (1a and 2a) activated by ethylalumium sesquichloride (EASC) displayed higher activities than did the aldimine-based Co(II) and Ni(II) complex (1A and 2A). The Co(II)-, Ni(II)-, and Fe(II)-based complexes exhibited different stereospecificities and afforded polybutadienes with different molecular weights due to the nature of the metal centre and the environment of the ligand. The imidoylchloride Co(II) complexes exhibited much better temperature tolerance, affording polymer in a high yield of 93.4% even at 80 °C.

•Fe(II), Co(II) and Ni(II) complexes with chlorinated bis(arylimino)pyridine ligands.•Distinctly different catalytic behaviors in ethylene polymerization was observed.•Bimodal PEs with predominately saturated chain ends were obtained for iron complexes.•Unimodal PEs with vinyl and saturated chain ends were obtained for cobalt complexes.A series of late-transition metal complexes supported with chlorinated bis(arylimino)pyridine ligands [2,6-(ArNCCl)2C5H3N]MtCl2 (Ar = 2,4,6-Me3C6H2, Mt = Fe (1a), Co (2a), Ni (3a); Ar = 2,6-iPr2C6H3, Mt = Fe (1b), Co (2b); Ar = 2,6-Et2C6H3, Mt = Co (1c), Ni (3c); Ar = 2,6-Me2C6H3, Mt = Fe (1d), Co (2d); Ar = 4-Cl-2,6-Me2C6H2, Mt = Fe (1e), Co (2e); Ar = 4-Br-2,6-Me2C6H2, Mt = Fe (1f), Co (2f)) were synthesized. At the presence of methylaluminoxane (MAO), Fe(II)- and Co(II)- based complexes were highly active towards ethylene polymerization, affording polymers with bimodal and unimodal molar mass distributions, respectively, while the Ni(II)-based complexes gave no polymer products. Moreover, the obtained polyethylenes were predominately saturated and vinyl-terminated for Fe(II)- and Co(II)-based complexes, respectively. Changing the ligand environment, polymerization parameters also posed a great influence on the catalytic activities and the properties of the resulting polymers.

Here, we report the first example of preparation of polyethylene (PE)/exfoliated-MoS2 nanocomposites through in-situ Ziegler-Natta polymerization. The exfoliated-MoS2/MgCl2-supported Ti-based Ziegler–Natta catalyst was synthesized via a facile coagglomeration method. The effects of MoS2 on the catalyst morphology and the ethylene polymerization behavior were examined. The resultant PE/MoS2 nanocomposites had a flake shape morphology, and the MoS2 fillers were well dispersed throughout the entire PE matrix. In addition, the thermal stability and mechanical properties of the PE base material were significantly enhanced by the introduction of a very small amount of the MoS2 filler (0.08 wt%). Therefore, this work provides a facile method to produce of high-performance PE.

•The activity of VOCl3 was improved with the electrochemical application.•Oxidation state of VOCl3 could be controlled by electrochemical method.•The polymerization mechanism does not change with the application of potential.A facile and efficient electrochemically assisted ethylene polymerization and ethylene-propylene copolymerization with the widely used VOCl3/ethylaluminum sesquichloride (EASC) catalyst system was demonstrated. The low-activity and/or inactive low-valence-state V species present in the catalyst were oxidized to high-valence-state V through electrochemical methodology. Thus, the catalytic activity of the VOCl3/EASC catalyst system was significantly improved. The effects of electrochemical application on the resultant polymer structure and properties were investigated. This work provides a new strategy to improve the performance of Ziegler-Natta catalysts.Download high-res image (94KB)Download full-size image

Lanthanide-based catalysts are highly active for isoprene polymerization in hexane. In this paper, a ternary catalyst consisting of neodymium neodecanoate {Nd(vers)3}, Al(iBu)3 and Al(iBu)2Cl was studied by using X-ray-absorption fine-structure (XAFS) technique. A sealed and moisture-proof liquid sample cell with adjustable thickness was designed for Nd LIII-edge XAFS measurements. Based on the XAFS data analysis, detailed structure changes around the Nd center were obtained. It was found that the Nd(vers)3 molecules formed an oligomer structure in hexane solution with two Nd–O subshells (5O @ 2.39 Å and 5O @ 2.54 Å) around the Nd center. The alkylation process by adding Al(iBu)3 to the hexane solution of Nd(vers)3 partially destroyed the aggregation degree of Nd(vers)3 molecules in hexane solution. Al(iBu)3 ligands were bonded to the Nd center by Nd–C bonding. With the Nd:Al ratio increasing from 1:2.5 to 1:10, the O neighbors around Nd decreased from 4 to 2 but with an unchanged Nd–O bond length of 2.38 Å, and the C neighbors around Nd were kept at ca. 4 with Nd–C bond lengths in the range of 2.57–2.58 Å. The Nd–O bonds can be further replaced by Nd–C bonds during the aging process. The chlorination process by adding Al(iBu)2Cl to the mixture solution of Nd(vers)3 and Al(iBu)3 restrained intensively the agglomeration of Nd(vers)3 molecules in hexane solution. Al(iBu)2Cl ligands were bonded to the Nd center by Nd–Cl bonds. There were about 3–4 C neighbors at 2.58 Å, 2 Cl neighbors at 2.87 Å, and 2 Al next-neighbors at 3.14 Å around the Nd center. After allowing the ternary catalyst to stand for 5 days, the coordination numbers of Nd–C and Nd–Cl were all stabilized to 3 without bond length changes, and partial single Cl− anions were also bonded to the Nd center. All these structural details and their change tendency demonstrate that the decrease of aggregation degree of Nd(vers)3 molecules in hexane solution can improve the catalytic activity of the ternary lanthanide-based catalyst system.