Synthesis of Branched Polyethylene via Bulky α-Diimine Nickel(II)-Catalyzed Ethylene Chain-Walking Polymerization

The catalysis of olefin polymerization through the chain-walking process is a subject of great interest. In this contribution, the successful synthesis of a Brookhart-type unsymmetrical α-diimine nickel catalyst Ni, which contains both dibenzhydryl and phenyl groups, was determined by X-ray crystallography. The compound has a pseudo-tetrahedral geometry at the Ni center, showing pseudo-C2-symmetry. Upon activation with modified methylaluminoxane (MMAO), Ni1 exhibits high catalytic activity up to 1.02 × 107 g PE (mol Ni h)−1 toward ethylene polymerization, enabling the synthesis of high molecular weight branched polyethylene. The molecular weights and branching densities could be tuned over a very wide range. The polymerization results indicated the possibility of precise microstructure control, depending on the polymerization temperature. The branching densities were decreased with increasing the polymerization temperature.

SILICA-SUPPORTED NICKEL AND ZIRCONIUM CATALYSTS FOR BRANCHED POLYETHYLENE

8-Aminoquinoline nickel dichloride and bis(cyclopentadienyl)zirconium dichloride (Cp_2ZrCl_2) were supportedsimultaneously on silica to produce branched polyethylene successfully by combined polymerization. The supportedpolymerization results showed that the molecular weight of polyethylene increased while the molecular weight distributionbecame wider and the molecular chains of oligomers remaning in the final solution became shorter as compared to theoligomers obtained in polymerization processes with pure 8-aminoquinoline nickel dichloride catalysis, as well as theCp_2ZrCl_2 and nickel combination system. With decreasing amount of Ni catalyst in the supported catalyst, the molecular chains of oligomers in the resulting solution became shorter, while α-olefin selectivity increased.

PREPARATION OF HIGHLY BRANCHED POLYETHYLENE WITH ACENAPHTHENEDHMINE NICKEL CHLORIDE/DIETHYLALUMINUM CHLORIDE CATALYST

The homogeneous catalyst system [ArN C（Nap）-C（Nap）=NAr]NiCl2 （Nap = 1,8-naphthdiyl, Ar = 2,6- diisopropylphenyl）/AlEt2Cl has been prepared and examined for ethylene polymerization. Polymerization conditions such as cocatalyst, Al/Ni molar ratio and polymerization temperature （Tp） have a great effect on catalytic activity and properties of polyethylenes （PE）. The activity of 5.1 × 10^5g PE/mol Ni. h was obtained by the catalyst, activated with AlEt2Cl at 120 of Al/Ni ratio and 30℃. Especially, Tp had a pronounced influence on branches and molecular weight of PE. Branching degree of PE increased with increasing temperature whereas their molecular weight decreased correspondingly. At Tp lower than about 70℃, the resultant PE was an elastic material. When Tp was higher than 70℃, the product was a viscous oil. The resultant PE was confirmed by ^13C-NMR to contain significant amounts of not only methyl but also ethyl, propyl, butyl, amyl, and longer branches （longer than six carbons）. According to gel permeation chromatographic measurement, the weightaverage molecular weights of the polymers obtained ranged from 3.6 × 10^3 to 2.3 × 10^5.

SYNTHESIS OF BRANCHED POLYETHYLENE USING (α-DIIMINE)NICKEL(Ⅱ)TiCl_4 COMBINED AND SUPPORTED CATALYST

Diimine)nickel {[C 6 H 5 -N = C(CH 3 ) - C(CH 3 ) = N - QH 5 ]NiBr 2 }-TiCl 4 , abbreviated as NiL-TiCl 4 combined catalyst which is supported on MgCl 2 -SiO 2 carrier has been prepared, by using alkyl aluminum (AlR 3 ) as the cocatalyst in place of methylaluminoxane (MAO) to catalyze ethylene oligomerization and copolymerization in situ. The influences of procedure for supporting NiL-TiCl 4 , the molar ratio of NiL to TiCl 4 , cocatalyst type and polymerization temperature on the catalytic performance were studied. The degree of branching and the composition of the branched chain of polymers produced have been investigated by IR and 13C-NMR spectra. The results show that the combined catalyst can synthesize the branched polyethylene with various banched chains .The polymerization reaction was monitored by gas chromatography and mass spectrometry (GC-MS). The results show that this catalyst promotes the oligomerization and copolymerization in situ for ethylene.

Linear/branched Block Polyethylene Produced by a-Diimine Nickel(Ⅱ)Catalyst and Bis(phenoxy-imine)Zirconium Binary Catalyst System in the Presence of Diethyl Zinc

In order to promote development of linear/branched block polyethylenes based on new catalytic systems,we synthesized a novel a.dimine nickel(Ⅱ)complex with isopropyl substituents on ortho-N-aryl and hydroxymethyl phenyl substituents on para-Naryl structures.The activity of a-dimine nickl(Ⅱ)catalyst was 3.02x10^(6)g-mol_(ni)^(-1)·h^(-1) at 70℃,and resultant polyethylene possessed 135/1000C branches.The linear/branched block polyethylenes were synthesized from ethylene polymerization catalyzed by the a-dimine nicke(Ⅱ)complex/bis(phenoxy-imine)zirconium in the presence of diethyI zinc.With the addition of ZnEtz(from 0 to 400),the melting peak of resultant polyethylene changed from a single melting peak to bimodal melting peaks.The molecular weights of resultant polyethylene ranging from 26.8 kg/mol to 17.1 kg/mol and PDI values varying gradually from 24.4 to 15.2 were obtained vla adjusting ZnEt;equiv.and molar ratio of two catalysts.In addition,the branching degree of the polyethylene increased from 13/1000C to 56/1000 with the increase of the proportion of a dimine nickel(Ⅱ)catalyst.Using this binary catalyst system,the reaction temperature of chain shutting polymerization can be carried out at 70℃,which is more conducive to industrial application.

A tarsus construct of a novel branched polyethylene with good elasticity for eyelid reconstruction in vivo

Branched polyethylene(B-PE)elastomer was investigated for its potential medical application as a tarsus construct.The in vitro results showed that the B-PE and processed B-PE films or scaffolds did not exhibit noticeable cytotoxicity to the NIH3T3 fibroblasts and human vascular endothelial cells(ECs).The B-PE scaffolds with a pore size of 280–480 mm were prepared by using a gelatin porogen-leaching method.The porous scaffolds implanted subcutaneously in rats exhibited mild inflammatory response,collagen deposition and fast fibrovascularization,suggesting their good biocompatibility.Quantitative real-time PCR analysis showed low expression of pro-inflammatory genes and up-regulated expressions of collagen deposition and vascularization-related genes,validating the results of historical evaluation in a molecular level.The B-PE scaffolds and Medpor controls were transplanted in rabbits with eyelid defects.The B-PE scaffolds exhibited a similar elastic modulus and provided desirable repair effects with mild fibrous capsulation,less eyelid deformities,and were well integrated with the fibrovascular tissue compared with the Medpor controls.

Gas Phase Polymerisation of Ethylene with Supported Titanium-Nickel Catalysts

A new ditransition-metal catalyst system TiC1.-NiC1_2,/MgC1_2,-SiO_2,/AlR_3 was prepared. Gas phase polymerization of ethylene with the catalysts has been studied. The kinetic curves of gas phase polymerization showed a decline. The catalysts efficiency and polymerization reaction rates have a optimum value when Ni content of the catalysts was 12.5%(mol).The products obtained are branched polyethylene.

Supporting of Nickel(Ⅱ) Acenaphthenediimine with Free Amino Group for Ethylene Polymerization

Bis （4-（4-amino-3, 5-diethylbenzyl）-2, 6-diethylphenylimino） acenaphthene] di- chloronickel （NiLCl2） was prepared and supported on SiO2 modified by methyl trichlorsilane（S-1） and on SiO2-MgCl2/TiCl4 （S-2） respectively. Two supported catalysts S-1 and S-2 used as catalysts for ethylene polymerization were studied and the influences of various polymerization conditions, including the polymerization temperature, cocatalysts, Al/Ni molar ratio on the catalytic activity, branching degree and branch length of PE were also investigated. The experimental results show that the supported catalysts exhibit higher catalytic activity for ethylene polymerization, the highest catalytic activity of S-1 using AlEt2Cl as cocatalyst at 50 ℃, reaching 5.8×10^5gPE/molNi·h, and needed lower Al/Ni molar ratio compared to homogeneous analogue.

Tandem Catalysis of One Metallocene Catalyst Combined with Two Different Cocatalysts for Preparing Branched Polyethylene

Tandem catalytic systems, consisting of ethylene bis（indenyl） zirconium dichloride with two different cocatalysts, alkylaluminum（diethylaluminium chloride or trialkylaluminum） and methylaluminoxane, were employed in preparing branched polyethylene from ethylene as sole monomer. The catalytic system rac-Et（Ind）2Zr Cl2/Al Et2Cl/MAO exhibited high incorporation（29.0/1000C）. The oligomerization and copolymerization reaction conditions in the tandem catalytic system, as well as the different cocatalysts, have effects on the catalytic activity and the properties of the obtained polymer, such as melting temperature, crystallinity, molecular weight and molecular weight distribution. Moreover, the oligomerization reaction condition is the main factor in altering the properties and structures of polyethylene.

High-Performanceα-Diimine Nickel Complexes for Facile Access of PE Elastomers with Exceptional Material Properties

For practicable elastomeric polyethylene,achieving high catalyst thermal stability and activity,along with precise control of polymer properties such as branching density,molecular weights,and distribution,is crucial but challenging.In this study,two sets of symmetricalα-diimine nickel complexes,each comprising four nickel bromide or chloride complexes,were synthesized and investigated their performance for ethylene polymerization under various reaction conditions.Upon activation with either Et2AlCl or MMAO cocatalysts,these complexes displayed not only high activity but also generated high molecular weight polyethylenes with controlled polydispersity and a substantial number of branches.The catalyst with the least steric hindrance displayed the remarkable high activity(up to 1.2×10^(7) g·mol^(-1)·h^(-1)).Notably,nickel bromides demonstrated higher activity compared to their chloride counterparts.The investigation into the effect of reaction temperature on catalytic performance revealed that NiBrMe-MMAO system displayed high thermal stability(activity up to 2.51×10^(6) g·mol^(-1)·h^(-1) at 100℃)and consistently yielded high polymer molecular weights with narrow polydispersity over a broad temperature range of 30-100℃.Of significant note,mechanical analysis of the resulting polyethylene demonstrated excellent ultimate tensile strength and high strain at break.Particularly,the polyethylene sample prepared at 100℃exhibited ultimate tensile strength up to 10 MPa with 1863%maximum strain at break and a strain recovery of up to 54.9%after ten cycles at a fixed strain of 300%,indicating excellent material properties of prepared thermoplastic polyethylene elastomers(TPE).