Unsymmetrical α‐diimine nickel (II) complex with rigid bicyclic ring ligand: Synthesis,characterization, and ethylene polymerization in the presence of AlEt2Cl

Unsymmetrical α‐diimine ligand 1 was successfully synthesized via condensation of trimethylaluminum (TMA) metalated 2‐methyl‐6‐isopropyl‐aniline with rigid bicyclic aliphatic diketone camphorquinone. Syn‐ and anti‐stereoisomers were detected by ¹³C NMR in the condensation product. The corresponding α‐diimine nickel (II) complex 1 was prepared from the exchange reaction of (DME)NiBr₂ with the ligand 1 , and displayed high activity for ethylene polymerization in the presence of diethylaluminum chloride (AlEt₂Cl). The resultant polymers were confirmed by gel permeation chromatography and ¹³C NMR characterization to be broad molecular weight distribution polyethylene with various branches, and high degree of branching, even at low polymerization temperature ?10°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of highly branched polyethylene using (α‐diimine) nickel complex covalently supported on modified SiO2

Bis(4‐(4‐amine‐3,5‐diisopropylbenzyl)‐2,6‐diisopropylphenylimino) acenaphthene NiBr₂ (Catalyst I) was synthesized. The complex covalently supported on Et₃Al‐treated silica (SC) and used for ethylene polymerization was produced with cocatalyst of common inexpensive alkylaluminum compounds. Polyethylenes (PEs) with branching numbers of 12.94 (1000C) to 116.02 (1000C) were prepared in heptane. The polymerization conditions, such as the cocatalyst, Al/Ni ratio, and temperature, had significant effects on catalytic activity and properties of polyethylenes. Confirmed by high‐temperature ¹³C NMR, the polyethylenes synthesized contain significant amounts of not only methyl but also ethyl, propyl, butyl, pentyl, and other long branches (longer than six carbons). The branching degree of polyethylenes increased with temperature, while their molecular weight and melting point decreased correspondingly, resulting in linear semicrystalline to totally amorphous polymers. The formation of the branches could be illustrated by the chain walking mechanism, which controlled their specific spacing and conformational arrangements with one another. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 103: 1483–1489, 2007     

The influence of various reaction parameters on the performance of (α‐diimine)nickel(II) catalysts in ethylene oligomerization reactions

Modified (α‐diimine)nickel(II) catalysts are suitable for ethylene oligomerization reactions. Due to the mechanism (“chain running”), the formation of double‐bond isomers and branched olefins can be observed. The obtained oligomer mixtures show a Schulz–Flory distribution. Increasing ethylene pressure favors the selectivity of α‐olefin formation. The same effect can be observed when Lewis bases like thiophene or furane are added to the oligomerization reaction mixture. These results can be related to an interaction of the additives with the catalytic active species during the oligomerization process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1356–1361, 2003     

Synthesis of acrylamide end‐functionalised poly(1‐hexene) using an α‐diimine nickel catalyst

The nickel precursor [bis(N,N′‐dimesitylimino)acenaphthene]dibromonickel and methylaluminoxane were used to catalyse the functionalisation of 1‐hexene with acrylamide by passivation of acrylamide with tri‐isobutylaluminium. The polymer obtained was characterised by GPC/SEC and NMR. The NMR experiments performed, COSY, DEPT, long‐range selective INEPT, HSQC and TOCSY 1D, showed that a 2,1 insertion of a single molecule of acrylamide per macromolecule had occurred at the end of the polyhexene chain. Copyright © 2004 Society of Chemical Industry     

Polymerization of styrene using bis(β‐ketoamino)nickel(II)/methylaluminoxane catalytic systems

Styrene (St) was polymerized in toluene solution by using bis(β‐ketoamino)nickel(II) complex as the catalyst precursor and methylaluminoxane (MAO) as the cocatalyst. The polymerization conditions, such as Al : Ni ratio, monomer concentration, reaction temperature, and polymerization time, were studied in detail. Both of the bis(β‐ketoamino)nickel(II)/MAO catalytic systems exhibited higher activity for polymerization of styrene, and polymerization gave moderate molecular weight of polystyrene with relatively narrow molecular weight distribution (M_w/M_n < 1.6). The obtained polymer was confirmed to be atactic polystyrene by analyzing the stereo‐triad distributions mm, mr, and rr of aromatic carbon C¹ in NMR spectrum of the polymer. The mechanism of the polymerization was also discussed and a metal–carbon coordination mechanism was proposed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Infrared study on in situ polymerization of zinc dimethacrylate in poly(α‐octylene‐co‐ethylene) elastomer

An infrared spectroscopic method was used to follow the course of in situ polymerization of zinc dimethacrylate (ZDMA) in poly(α‐octylene‐co‐ethylene) elastomer (POE). The integral intensity of the 831 cm^?1 band, ie the out‐of‐plane deformation mode of ?CH, was used to determine the residual amount of ZDMA in composites cured at 165°C for different times, through which the course of in situ polymerization of ZDMA in POE was traced and the dynamic curve determined. The curing course of the ZDMA/POE/peroxide system at 165°C was examined with a rheometer and compared with the course of in situ polymerization. The results surprisingly show that the in situ polymerization of ZDMA is almost complete at the beginning stage of curing, and that substantial crosslinking starts subsequently. Scanning electron microscopy and transmission electron microscopy observations on morphologies of ZDMA/POE composites cured at 165°C for different times were carried out and confirmed the results of infrared experiments. Combining all the investigations, it was deduced that a competition exists between in situ polymerization and crosslinking in the composites. Covalent crosslinking rather than ionic bond crosslinks are the major types of crosslinks structures in ZDMA/POE composites, and its total density is lower than that of carbon‐ black‐reinforced POE. Copyright © 2004 Society of Chemical Industry     

Synthesis of reactor blend of linear and branched polyethylene using metallocene/Ni‐diimine binary catalyst system in a single reactor

This work reports the synthesis of a series of reactor blends of linear and branched polyethylene materials using a combination of [1,4‐bis(2,6‐diisopropylphenyl) acenaphthene diimine nickel(II) dibromide] ( 1 )/MMAO, known as an active catalyst for the production of branched polyethylene, and [rac‐ethylenebis(indenyl) zirconium dichloride] ( 2 )/MMAO, which is active for the production of linear polyethylene. The polymerization runs were performed at various levels of temperature, pressure, and catalyst 2 molar fractions. At 5°C, there was very low influence of catalyst 2 molar fraction on the overall catalyst activity. However, at 30°C and 50°C, the overall catalyst activity increased linearly with catalyst 2 molar fraction. The same linear dependency was also found for the polymerization reactions carried out at 60°C and 100°C. At various levels of temperature and ethylene pressure, higher melting temperature and crystallinity were observed with an increase in catalyst 2 molar fraction. At 60°C and 100 psig, the DSC thermograms of the polymers produced with 1 / 2 /MMAO exhibited two distinct peaks with melting temperatures closely corresponding to the melting temperatures of the polymers produced with the individual catalysts, 1 /MMAO and 2 /MMAO. The GPCV analysis of all polyethylene samples showed monomodal molecular weight distributions with low polydispersities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2212–2217, 2005     

Cationic copolymers of α,β‐poly‐(N‐2‐hydroxyethyl)‐DL‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy): synthesis and characterization

In the present study the derivatization of two water‐soluble synthetic polymers, α,β‐poly(N‐2‐hydroxyethyl)‐DL ‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy), with glycidyltrimethylammonium chloride (GTA) is described. This reaction permits the introduction of positive charges in the macromolecular chains of PHEA and PAHy in order to make easier the electrostatic interaction with DNA. Different parameters affect the reaction of derivatization, such as GTA concentration and reaction time. PHEA reacts partially and slowly with GTA; on the contrary the reaction of PAHy with GTA is more rapid and extensive. The derivatization of PHEA and PAHy with GTA is a convenient method to introduce positive groups in their chains and it permits the preparation of interpolyelectrolyte complexes with DNA. © 2000 Society of Chemical Industry     

Ruthenium(II)‐Catalyzed Protocol for Preparation of Diverse α,β‐ and β,β‐Dihaloenones from Diazodicarbonyls

Efficient one‐step syntheses of α,β‐ and β,β‐dihaloenones were achieved by ruthenium(II)‐catalyzed reactions between cyclic or acyclic diazodicarbonyl compounds and oxalyl chloride or oxalyl bromide in moderate to good yields. This methodology offers several significant advantages, which include ease of handling, mild reaction conditions, one‐step reaction, and the use of an effective and non‐toxic catalyst. The synthesized compounds were further transformed into highly functionalized novel molecules bearing aromatic rings on the enone moiety using the Suzuki reaction.

     

Copolymerization of ethylene/α‐olefins over (2‐MeInd)2ZrCl2/MAO and (2‐BzInd)2ZrCl2/MAO systems

Ethylene homopolymerization and ethylene/α‐olefin copolymerization were carried out using unbridged and 2‐alkyl substituted bis(indenyl)zirconium dichloride complexes such as (2‐MeInd)₂ZrCl₂ and (2‐BzInd)₂ZrCl₂. Various concentrations of 1‐hexene, 1‐dodecene, and 1‐octadecene were used in order to find the effect of chain length of α‐olefins on the copolymerization behavior. In ethylene homopolymerization, catalytic activity increased at higher polymerization temperature, and (2‐MeInd)₂ZrCl₂ showed higher activity than (2‐BzInd)₂ZrCl₂. The increase of catalytic activity with addition of comonomer (the synergistic effect) was not observed except in the case of ethylene/1‐hexene copolymerization at 40°C. The monomer reactivity ratios of ethylene increased with the decrease of polymerization temperature, while those of α‐olefin showed the reverse trend. The two catalysts showed similar copolymerization reactivity ratios. (2‐MeInd)₂ZrCl₂ produced the copolymer with higher M_w than (2‐BzInd)₂ZrCl₂. The melting temperature and the crystallinity decreased drastically with the increase of the α‐olefin content but T_m as a function of weight fraction of the α‐olefins showed similar decreasing behavior. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 928–937, 2000     

Efficient Synthesis of β,γ‐Alkynyl α‐Amino Acid Derivatives by Ag(I)‐Catalyzed Alkynylation of α‐Imino Esters

The first catalytic synthesis of β,γ‐alkynyl α‐amino acid derivatives was achieved by direct addition of terminal alkynes to α‐imino esters in the presence of an Ag(I) salt under mild reaction conditions.     

Influence of support friability and concentration of α‐olefins on gas‐phase ethylene polymerization over polymer‐supported metallocene/methylaluminoxane catalysts

The effects of support friability (Φ) and ethylene/comonomer ratios were investigated over supported metallocene/methylaluminoxane catalysts prepared with nine different porous polymeric supports and various comonomer concentrations with a 2‐L reactor operated in the semibatch gas‐phase mode at 80°C and 1.4 MPa. Φ of the supports was measured with a newly devised method. The performance of the supported catalysts depended on support Φ as follows. The average homopolymerization activities varied from less than 6 t of polyethylene (PE) (mol of Zr)^?1 h^?1 for low‐Φ catalysts to 10–20 t of PE (mol of Zr)^?1 h^?1 for moderate‐Φ catalysts and up to 100 t of PE (mol of Zr)^?1 h^?1 for the high‐Φ catalysts. The presence of 1‐hexene and propylene comonomers increased the activity of the low‐Φ catalysts by up to 20‐fold and 50‐fold, respectively; that is, there were very marked comonomer effects. Activity enhancement by 1‐hexene was less than 3‐fold for the moderate‐Φ catalysts, whereas the high‐Φ catalysts showed little activity enhancement. Sometimes, 1‐hexene even resulted in activity reductions. Very different particle morphologies were obtained with the catalysts of different Φ's. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 514–527, 2007     

Polymerisation of ethylene catalysed by mono‐imine‐2,6‐diacetylpyridine iron/methylaluminoxane (MAO) catalyst system: effect of the ligand on polymer microstructure

The complex, {1‐{6‐[(2,6‐diisopropylphenyl)‐ethaneimidoyl]‐2‐pyridinyl}‐1‐ethanone}iron(II) dichloride ( 2 ), has been synthesised and characterised. Treatment of complex 2 with methylaluminoxane resulted in a very active catalytic system for the preparation of polyethylene (PE). The system shows activities in the order of magnitude 10⁷ g (PE) mol^?1(Fe) h^?1 bar^?1. Characterisation by ¹³C NMR indicated that branched PE was obtained and that experimental conditions affect polymer microstructure. PE produced contained six to eight branches per 100 carbons. © 2002 Society of Chemical Industry     

Synthesis of polar vinyl monomer–olefin copolymers by α‐diimine nickel catalyst

Vinyl acetate, methyl methacrylate, acrylonitrile and methyl vinyl ketone were investigated for co‐ and terpolymerization with ethylene and ethylene–propylene. Precursor [bis(N,N ′‐dimesitylimino)acenaphthene]dibromonickel, activated by methylaluminoxane was used as a catalyst system and trialkylaluminium was employed to block the polar groups for these polymerizations. Polymerization activities of the order of magnitude of 10⁶ in the case of vinyl acetate and methyl methacrylate, and 10⁵ in the case of acrylonitrile were achieved. Microanalysis and GPC of acrylonitrile copolymers found about 17 units of acrylonitrile per polymer chain. Copolymers with very different properties from the parent homopolymers were obtained in all cases except that of methyl vinyl ketone. © 2001 Society of Chemical Industry     

Direct Decarboxylative Alkynylation of α,α‐Difluoroarylacetic Acids under Transition Metal‐Free Conditions

An efficient and generally applicable protocol for decarboxylative coupling of α,α‐difluoroarylacetic acids with ethynylbenziodoxolone (EBX) reagents has been developed, affording α,α‐difluoromethylated alkynes bearing various functional groups in moderate to excellent yields. Remarkably, this potassium persulfate (K₂S₂O₈)‐promoted reaction employs water as solvent under transition metal‐free conditions, thus providing a green synthetic approach to α,α‐difluoromethylated alkynes.

     

Synthesis and characterization of polyrotaxanes comprising α‐cyclodextrins and poly(ε‐caprolactone) end‐capped with poly(butyl methacrylate)s

Biodegradable polyrotaxane‐based triblock copolymers were synthesized via the bulk atom transfer radical polymerization (ATRP) of n‐butyl methacrylate (BMA) initiated with polypseudo‐rotaxanes (PPRs) built from a distal 2‐bromoisobutyryl end‐capped poly(ε‐caprolactone) (Br‐PCL‐Br) with α‐cyclodextrins (α‐CDs) in the presence of Cu(I)Br/N,N,N′,N″,N″‐pentamethyldiethylenetriamine at 45 ºC. The structure was characterized in detail by means of ¹H NMR, gel permeation chromatography, wide‐angle X‐ray diffraction, DSC and TGA. When the feed molar ratio of BMA to Br‐PCL‐Br was changed from 128 to 300, the degree of polymerization of PBMA blocks attached to two ends of the PPRs was in the range 382 ? 803. Although about a tenth of the added α‐CDs were still threaded onto the PCL chain after the ATRP process, the movable α‐CDs made a marked contribution to the mechanical strength enhancement, blood anticoagulation activity and protein adsorption repellency of the resulting copolymers. Meanwhile, they could also protect the copolymers from the attack of H₂O and Lipase AK Amano molecules, exhibiting a lower mass loss as evidenced in hydrolytic and enzymatic degradation experiments. © 2013 Society of Chemical Industry     

Synthesis and characterization of elastoplastic poly(styrene‐co‐ethylene) using novel mono(η5‐cyclopentadienyl) titanium and modified methylaluminoxane catalysts

Elastoplastic poly(styrene‐co‐ethylene) with high molecular weight was synthesized using novel mono(η⁵‐pentamethylcyclopentadienyl)tribenzyloxy titanium [Cp*Ti(OBz)₃] complex activated with four types of modified methylaluminoxanes (mMAO) containing different amounts of residual trimethylaluminum (TMA). The ideal mMAO, used as a cocatalyst for the copolymerization of styrene with ethylene, contains TMA approaching to 17.8 wt %. The oxidation states of the titanium‐active species in different Cp*Ti(OBz)₃/mMAO catalytic systems were determined by the redox titration method. The results show that both active species may exist in the current system, where one [Ti(IV)] gives a copolymer of styrene and ethylene, and the second one [Ti(III)] only produces syndiotactic polystyrene (sPS). Catalytic activity, compositions of copolymerization products, styrene incorporation, and copolymer microstructure depend on copolymerization conditions, including polymerization temperature, Al/Ti, molar ratio, and comonomers feed ratio. The copolymerization products were fractionated by successive solvent extractions with boiling butanone and tetrahydrofuran (THF). The copolymer, chiefly existing in THF‐soluble fractions, was confirmed by ¹³C‐NMR, GPC, DSC, and WAXD to be an elastoplastic copolymer with a single glass transition temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1851–1857, 1999     

Multi‐Enzymatic Synthesis of Optically Pure β‐Hydroxy α‐Amino Acids

A novel enzymatic production system of optically pure β‐hydroxy α‐amino acids was developed. Two enzymes were used for the system: an N‐succinyl L ‐amino acid β‐hydroxylase (SadA) belonging to the iron(II)/α‐ketoglutarate‐dependent dioxygenase superfamily and an N‐succinyl L ‐amino acid desuccinylase (LasA). The genes encoding the two enzymes are part of a gene set responsible for the biosynthesis of peptidyl compounds found in the Burkholderia ambifaria AMMD genome. SadA stereoselectively hydroxylated several N‐succinyl aliphatic L ‐amino acids and produced N‐succinyl β‐hydroxy L ‐amino acids, such as N‐succinyl‐L ‐β‐hydroxyvaline, N‐succinyl‐L ‐threonine, (2S,3R)‐N‐succinyl‐L ‐β‐hydroxyisoleucine, and N‐succinyl‐L ‐threo‐β‐hydroxyleucine. LasA catalyzed the desuccinylation of various N‐succinyl‐L ‐amino acids. Surprisingly, LasA is the first amide bond‐forming enzyme belonging to the amidohydrolase superfamily, and has succinylation activity towards the amino group of L ‐leucine. By combining SadA and LasA in a preparative scale production using N‐succinyl‐L ‐leucine as substrate, 2.3 mmol of L ‐threo‐β‐hydroxyleucine were successfully produced with 93% conversion and over 99% of diastereomeric excess. Consequently, the new production system described in this study has advantages in optical purity and reaction efficiency for application in the mass production of several β‐hydroxy α‐amino acids.

     

Synthesis and thermal behavior of poly(methyl methacrylate)/Maghnia bentonite nanocomposite prepared at room temperature via in situ polymerization initiated by a new Ni(II)α‐benzoinoxime complex

Poly(methyl methacrylate) (PMMA) and poly(methyl methacrylate)/clay nanocomposite (PMMA/OBT) were successfully prepared in dioxan at room temperature via in situ radical polymerization initiated by a new Ni(II)α‐ Benzoinoxime complex as a single component in presence of 3% by weight of an organically modified bentonite (OBT) (originated from Maghnia, Algeria) and characterized by FTIR, ¹H‐NMR and viscometry. Mainly intercalated and partially exfoliated PMMA/OBT nanocomposite was elaborated and evidenced by X‐Ray diffraction (XRD) and transmission electron microscopy (TEM). The intrinsic viscosity of PMMA/OBT nanocomposite is much higher than the one of pure PMMA prepared under the same conditions. Differential scanning calorimetry (DSC) displayed an increase of 10°C in the glass transition temperature of the elaborated PMMA/OBT nanocomposite relative to the one of pure PMMA. Moreover, the TGA analysis confirms a significant improvement of the thermal stability of PMMA/OBT nanocomposite compared to virgin PMMA: the onset degradation temperature of the nanocomposite, carried out under nitrogen atmosphere, increased by more than 45°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Maghnite‐H+, a solid catalyst for the cationic polymerization of α‐methylstyrene

The polymerization of α‐methylstyrene (AMS) catalyzed by Maghnite‐H⁺ (Mag‐H) was investigated. Mag‐H is a montmorillonite sheet silicate clay, exchanged with protons. It was found that the cationic polymerization of AMS is initiated by Mag‐H at ambient temperature in bulk and in solution. The effect of the amount of Mag‐H, the temperature, and the solvent was studied. The polymerization rate increased with increase in the temperature and the proportion of catalyst, and it was larger in nonpolar solvents. These results indicated the cationic nature of the polymerization. It may be suggested that the polymerization is initiated by proton addition to monomer from Mag‐H. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008