Organometallics in ethylene polymerization with a catalyst system TiCl4/Al(C2H5)2Cl/Mg(C6H5)2: 2. Polymerization process in pseudo-solution

A study has been made of ethylene polymerization in pseudo-solution with a catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂ in the presence of hydrogen as a regulator of polyethylene molecular weight. The polymerization process in pseudo-solution by adjustment of hydrogen makes it possible to produce polyethylene having a wide range of molecular weights. For this purpose melt indices between 0°–50°C/min are desirable and these values are not reached with a suspension type of ethylene polymerization with a catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂. The effect of the molar ratio cocatalyst/catalyst (Al/Ti and Mg/Ti) on the catalyst activity and on the polyethylene molecular weight was studied, together with the content of hydrogen as a regulator of the molecular weight. The catalyst productivity increased to some limiting molar ratio Mg/Ti and Al/Ti and further increase of organometallics in the catalyst system did not influence the polymer molecular weight. In the case of ethylene polymerization with this catalyst combination in the presence of hydrogen, some activation of the catalyst was observed. Two mechanisms, which may account for the activation effect of the hydrogen are discussed.     

Synthesis of branched polyethylene by ethylene homopolymerization with a novel (α‐diimine)nickel complex in the presence of methylaluminoxane

Branched polyethylene (PE) was prepared with a novel (α‐diimine)nickel(II) complex of 2,3‐bis(2,6‐dimethylphenyl)‐butanediimine nickel dichloride {[2,6‐(CH₃)₂C₆H₃? N?C(CH₃)C(CH₃)?N? 2,6‐(CH₃)₂C₆H₃]NiCl₂} activated by methylaluminoxane in the presence of a single ethylene monomer. The influences of various polymerization conditions, including the temperature, Al/Ni molar ratio, Ni catalyst concentration, and time, on the catalytic activity, molecular weight, degree of branching, and branch length of PE were investigated. According to gel permeation chromatography, the weight‐average molecular weights of the polymers obtained ranged from 1.7 × 10⁵ to 6.0 × 10⁵, with narrow molecular weight distributions of 2.0–3.5. The degree of branching in the polymers rapidly increased with the polymerization temperature increasing; this led to highly crystalline to totally amorphous polymers, but it was independent of the Al/Ni molar ratio and catalyst concentration. At polymerization temperatures greater than 20°C, the resultant PE was confirmed by ¹³C‐NMR to contain significant amounts of not only methyl but also ethyl, propyl, butyl, amyl, and long branches (longer than six carbons). The formation of the branches could be illustrated by the chain walking mechanism, which controlled their specific spacing and conformational arrangements with one another. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1123–1132, 2002; DOI 10.1002/app.10398     

Organometallics in ethylene polymerization with a catalyst system TiCl4/Al(C2H5)2Cl/Mg(C6H5)2: 1. Suspension polymerization process

Suspension polymerization of ethylene with the catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂, at different molar ratios Mg/Ti and Al/Ti, was studied. The transition metal compounds in the catalyst complex formed in this system were found to consist only of Ti(II) and Ti(III), without free Ti(IV); but even with a Ti(II) content of 30% the catalyst was highly active. The influence of the molar ratio cocatalyst/catalyst (Al/Ti and Mg/Ti) on the catalyst activity and on the polyethylene molecular weight was studied, together with the reduction of TiCl₄ by Al(C₂H₅)₂Cl and Mg(C₆H₅)₂ in the reduction step. The polymer yield increased to some limiting molar ratio Mg/Ti and to some limit ratio Al/Ti and further increase of organometal concentration in the system has practically no influence on the catalyst productivity. Dependence of the polyethylene molecular weight on the molar ratios Mg/Ti and Al/Ti was observed, proving the presence of chain transfer reactions with organometallics.     

Addition polymerization of norbornene, 5-vinyl-2-norbornene and 2-methoxycarbonyl-5-norbornene with a catalyst based on a palladium(0) precursor complex

Pd(dibenzylideneacetone)₂, when activated in situ with 1 equiv of [CPh₃][B(C₆F₅)₄] in the presence of 1 equiv of P(C₆H₁₁)₃, efficiently catalyzed the addition polymerization and copolymerization of norbornene and its derivatives. Homopolymerization of 5-vinyl-2-norbornene took place regio-selectively with the endo-cyclic double bond to give high-molecular weight polymers, while the exocyclic double bond remained intact so that the resulting polymer had pendent vinyl groups along the polymer chain. In the polymerization of a mixture of the endo-/exo- isomers of 2-methoxycarbonyl-5-norbornene, the endo-isomer was consumed prior to consumption of the exo-isomer, contrary to the well-known tendency in Pd(II)-based catalyst systems. Another notable feature of the present catalytic system was the strong dependency of the molecular weight on the reaction temperature, which was studied in detail for the copolymerization of 2-methoxycarbonyl-5-norbornene with norbornene: we could control the molecular weight without the use of a chain transfer agent. The extracted oligomeric fraction of poly(norbornene) showed the presence of a terminal CC double bond as well as a C₆F₅ unit that was bound to the first norbornane unit in the polymer chain.     

Reversible pressure-induced polymerization of Fe(C5H5)2 doped C70

High pressure Raman, IR and X-ray diffraction (XRD) studies have been carried out on C₇₀(Fe(C₅H₅)₂)₂ (hereafter, “C₇₀(Fc)₂”) sheets. Theoretical calculation is further used to analyze the Electron Localization Function (ELF) and charge transfer in the crystal and thus to understand the transformation of C₇₀(Fc)₂ under pressure. Our results show that even at room temperature dimeric phase and one dimensional (1D) polymer phase of C₇₀ molecules can be formed at about 3 and 8 GPa, respectively. The polymerization is found to be reversible upon decompression and the reversibility is related to the pressure-tuned charge transfer, as well as the overridden steric repulsion of counter ions. According to the layered structure of the intercalated ferrocene molecules formed in the crystal, we suggest that ferrocene acts as not only a spacer to restrict the polymerization of C₇₀ molecules within a layer, but also as charge reservoir to tune the polymerization process. This supplies a possible way for us to design the polymerization of fullerenes at suitable conditions.     

Synthesis of (C5H5)2Zr(O2C)CH3 and (C5H5)2Zr(O2C)CH2CH3 for olefin polymerization

Summary (C₅H₅)₂Zr(O₂C)CH₃ and (C₅H₅)₂Zr(O₂C)CH₂CH₃ complexes were synthesized, characterized and activated with MAO for ethylene polymerization. The highest catalytic activity was achieved at Al/Zr molar ratio of 3000 for both systems. The effects of the size of the R group in the carboxylate ligands, the Al/Zr molar ratio and reaction temperature on the catalytic activity and polymer properties were studied and discussed.     

Thermal decomposition of C2H5I on Ag(111)

The decomposition of C₂H₅I on Ag(111) has been studied using temperature programmed desorption (TPD), work-function change measurements () and X-ray photoelectron spectroscopy (XPS). Adsorption of C₂H₅I at 100 K is mostly molecular with little dissociation. C-I bond cleavage starts around 110 K. Below 1 monolayer coverage, all adsorbed C₂H₅I(a) dissociates to C₂H₅(a) and I(a) during TPD. C₂H₅(a) undergoes only recombination, producing gas phase butane (C₄H₁₀) around 190 K. No C-H or C-C bond cleavage takes place. On D/Ag(111), hydrogenation of C₂H₅(a) to C₂H₅(g) occurs readily between 150 and 220 K.     

Preparation and properties of ABA block polymers of styrene and butadiene or isoprene made with sec-C4H9Li·2(C2H5)2O

ABA-type “tapered” block polymers were prepared from styrene (monomer A) and butadiene or isoprene, using an initiator of sec-butyllithium complexed with two molecules of ethyl ether. The stress–strain curves of polymers containing about 20–50% styrene show the usual resemblance to curves of crosslinked elastomers. The SBS polymers had higher tensile strengths than the SIS polymers. They also had slightly higher tensile strengths than comparable SBS polymers made with sec-butyllithium. The SIS polymers, however, had generally lower tensile strengths than those made with sec-butyllithium. This is probably caused by higher styrene content of the isoprene block, brought about by increased randomization of the styrene–isoprene copolymerization due to the presence of the ether. The A and B blocks become more compatible, producing loss of strength in the polymer. Infrared analyses of polydienes made with the sec-C₄H₉Li·2(C₂H₅)₂O initiator showed a 6% to 8% increase in 1,2-content (for polybutadiene) or 3,4-content (for polyisoprene), compared to polymers made with sec-butyllithium. The polymer microstructures still have high (>80%) total 1,4-content, however. Thus, this amount of ether can be tolerated in the polymerization system without great loss of rubbery properties or block structure in the resultant polymers.     

Ethylene polymerization catalyzed by diamide complexes of Ti(IV) and Zr(IV)

In this research, we describe the application of the complexes o‐C₆H₄(NSiMe₃)₂ZrCl₂ ( 1 ), o‐C₆H₄(NSiMe₃)₂TiBr₂ ( 2 ), o‐C₆H₄(NSiMe₃)₂TiCl₂ ( 3 ), C₂H₄(NSiMe₃)₂ZrCl₂ ( 4 ), in the ethylene polymerization with different Al/M ratios and temperatures. These complexes presented significant catalytic activities in the presence of methyaluminoxane (MAO) as cocatalyst and toluene as solvent, producing high molecular weight linear polyethylenes. Zirconium complexes were more active at 60°C and titanium complexes at 40°C. Zirconium complex ( 1 ) showed the best values of activity (347 kg PE/mol Zr h atm) for Al/Zr ratio of 340 and 60°C of temperature. In ethylene‐1‐hexene copolymerization, the best result was also reached with catalyst 1 , at the same conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polymerization of ethylene by zirconocene—B(C6F5)3catalysts with aluminum compounds

Ethylene polymerization by zirconocene—B(C₆F₅)₃ catalysts with various aluminum compounds has been investigated. It is found that the catalytic activity depended on zirconocenes used, and especially on the type of aluminum compounds. For Et(H₄Ind)₂ZrCl₂ (H₄Ind: tetrahydroindenyl), the activity decreases in the following order: Me₃Al > i-Bu₃Al > Et₃Al ≫ Et₂AlCl. While for Cp₂ZrCl₂(Cp : cyclopentadienyl), it varies as follows: i-Bu₃Al > Me₃Al ≫ Et₃Al. Furthermore, the activity is significantly affected by the addition mode of the catalytic components, which may imply that the formation of active centers is associated with an existing concentration of catalytic components. Results of thermal behavior of polyethylene (PE) studied by differential scanning calorimetry (DSC) show that crystallinity of the polymer prepared with Et₃Al is higher than that with Me₃Al or i-Bu₃Al. It is also found that the number-average molecular weight (M ) of the polymers prepared with Me₃Al or i-Bu₃Al is much higher than that with Et₃Al. ¹H-NMR studies substantiate that i-Bu₃Al is a more efficient alkylation agent of Cp₂ZrCl₂ in comparison with Me₃Al. © 1997 John Wiley & Sons, Inc. JAppl Polym Sci 66: 1715–1720, 1997     

Synthesis of monodisperse poly(butyl acrylate) initiated by SmMe(C5Me5)2(THF) and its adhesive properties after crosslinking by electron‐beam irradiation

Polymerization reactions of butyl acrylate (BuA) were carried out using an organosamarium complex, SmMe(C₅Me₅)₂(THF), as an initiator. Polymerization proceeds quantitatively to give high number‐average molecular mass polymers (M_n > 200,000) and narrow molecular weight distributions (M_w/M_n < 1.07). Irradiation of the resulting poly(BuA) with an electron beam (EB) gave crosslinked poly(BuA). Improved viscoelastic and adhesive properties of these polymers were useful for high‐temperature applications. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 432–437, 2001     

Preparation of heterotactic-rich poly(methyl methacrylate) with narrow molecular weight distribution bytert-butyllithium/bis(2,6-di-tert-butylphenoxy)methylaluminum

Summary Polymerization of methyl methacrylate (MMA) withtert-butyllithium (t-C₄H₉Li) in toluene in the presence of aluminum alkoxides such as ethoxide,tert-butoxide and 2,6-di-tert-butylphenoxide, were examined at various Al/Li ratios. In the cases of ethoxide andtert-butoxide, predominantly isotactic polymers with broad molecular weight distribution were obtained. Combinations oft-C₄H₉Li and bis(2,6-ditert-butylphenoxy)methylaluminum [MeAl(ODBP)₂] were found to be an efficient initiating system for heterotactic polymerization of MMA, which gives PMMA rich in heterotactic triads up to 68% with narrow molecular weight distribution (Mw/Mn=1.09–1.17). End group analysis by¹H NMR indicated thatt-C₄H₉Li initiates the polymerization and MeAl(ODBP)₂ works as a stereospecific modifier. From stereosequence analysis of the heterotactic PMMA by¹³C NMR, it was found that the calculated pentad fractions from the first-order Markovian statistics (Pm/r=0.742, Pr/m=0.627) fitted the observed ones better than those from Bernoullian statistics. The glass transition temperature of the heterotactic PMMA was 13°C lower than that of syndiotactic PMMA, and the intrinsic viscosity in tetrahydrofuran was close to that of isotactic PMMA with a similar molecular weight but higher than that of syndiotactic PMMA.     

Polymerization of styrene using pyrazolylimine nickel (II)/methylaluminoxane catalytic systems

The polymerization of styrene with two pyrazolylimine nickel (II) complexes of (2-(C₃HN₂Me₂-3, 5)(C(Ph) = N(4-R₂C₆H₂(R₁)₂-2, 6)NiBr₂ (Complex 1 , R₁ = ⁱPr, R₂ = H; Complex 2 , R₁ = H, R₂ = NO₂)) activated by methylaluminoxane was studied. The influences of polymerization parameters such as polymerization temperature, Al/Ni molar ratio, and reaction time on catalytic activity and molecular weight of the polystyrene (PS) were investigated in detail. The electron-withdrawing of nitro group in Complex 2 could not enhance the catalytic activity for styrene polymerization; however, the molecular weights of polymers were increased. Both of the two catalytic systems exhibited high activity [up to 8.45 × 10⁵ gPS/(mol Ni h)] for styrene polymerization and provide PS with moderate to low-molecular weights (M_w = 2.21 × 10⁴∼ 5.71 × 10³ g/mol) and narrower molecular weight distributions about 2.0. The obtained PS were characterized by means of IR, ¹H NMR, and ¹³C NMR techniques. The results indicated that the PS was atactic polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Notable Effects of Aluminum Alkyls and Solvents for Highly Efficient Ethylene (Co)polymerizations Catalyzed by (Arylimido)‐ (aryloxo)vanadium Complexes

The effects of both Al cocatalyst and solvent on catalytic activity in the ethylene polymerization by the (arylmido)(aryloxo)vanadium(V) complex, VCl₂(N‐2,6‐Me₂C₆H₃)(O‐2,6‐Me₂C₆H₃) ( 1 ), have been explored in detail. The activity of 5.84×10⁵ kg PE/mol V⋅h (TOF 2.08×10⁷ h⁻¹) has been achieved by 1 /EtAlCl₂ catalyst in CH₂Cl₂ at 0 °C, and the activity in toluene increased in the order: i‐Bu₂AlCl>EtAlCl₂>Me₂AlCl>Et₂AlCl> Et₂Al(OEt), AlEt₃, AlMe₃ (negligible activities). Both aluminum alkyl cocatalyst and solvent also affected the catalytic activity and the norbornene (NBE) incorporation in the ethylene/NBE copolymerization using complex 1 , whereas the NBE contents were not strongly affected by the kind of aryl oxide ligand in VCl₂(N‐2,6‐Me₂C₆H₃)(OAr) [OAr=O‐2,6‐Me₂C₆H₃ ( 1 ), O‐2,6‐i‐Pr₂C₆H₃ ( 2 ), O‐2,6‐Ph₂C₆H₃ ( 3 )].     

Polymerization of β-pinene with ethylaluminum dichloride (C2H5AlCl2)

The main goal of this work is to study the cationic polymerization of terpenes, particularly of β-pinene, with alkylaluminum catalysts. Some experiments at different polymerization temperatures (10, 20, and 50°C) were carried out with ethylaluminum dichloride catalyst, C₂H₅AlCl₂. From the results, it is possible to draw some general conclusions about the evolution of chain growth during polymerization. This work also includes the influence of reaction temperature on some properties of the final resin, particularly the molecular weight distribution, the softening point, and the Gardner color index. The role of reducing agents, such as iodine, during the distillation of the final resin is also evaluated with respect to color and softening point. As a result of this investigation, the Mark–Howink constants for terpene resins in toluene and dicloromethane as solvents have also been experimentally determined, thus allowing a more precise use of size exclusion chromatography in the characterization of such natural based products. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2558–2565, 2001     

Ethylene/1‐octadecene copolymerization using [η5:η1‐C5Me4‐4‐R1‐6‐R‐C6H2O]TiCl2 catalysts

Copolymerization of ethylene with 1‐octadecene was studied using [η⁵:η¹‐C₅Me₄‐4‐R₁‐6‐R‐C₆H₂O]TiCl₂ [R₁ = ^tBu (1), H (2, 3, 4); R = ^tBu (1, 2), Me (3), Ph (4)] as catalysts in the presence of Al(i‐Bu)₃ and [Ph₃C][B(C₆F₅)₄]. The effect of the concentration of comonomer in the feed and Al/Ti molar ratio on the catalytic activity and molecular weight of the resultant copolymer were investigated. The substituents on the phenyl ring of the ligand affect considerably both the catalytic activity and comonomer incorporation. The 1 /Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄] catalyst system exhibits the highest catalytic activity and produces copolymers with the highest molecular weight, while the 2 /Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄] catalyst system gives copolymers with the highest comonomer incorporation under similar conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polymerization of ethylene by chromium acetylacetonate/methylaluminoxane catalyst system

Summary The present paper deals with polymerization of ethylene by chromium acetylacetonate - Cr(acac)₃ - activated by alkylaluminium, e.g. Al(C₂H₅)₃ or Al(i-C₅H₉)₃, or methylaluminoxane (MAO). The influence of polymerization parameters on catalyst performance, such as Al/Cr mole ratio, temperature, aging time, type of cocatalyst, was investigated. High activities were obtained only when MAO was the cocatalyst. The polymers were characterized by size exclusion chromatography (SEC) and differential scanning calorimetry (DSC) analyses. Received: 11 September 1997/Revised version: 5 January 1998/Accepted: 20 March 1998     

Lewis Pair Polymerization of Acrylic Monomers by N-Heterocyclic Carbenes and B(C6F5)3

This work has uncovered the first highly active and efficient Lewis pair polymerization (LPP) system based on N-heterocyclic carbene (NHC)/B(C₆F₅)₃ pairs for converting acrylic monomers into medium- to high-molecular weight polymers. The study has systematically examined steric and electronic effects of three 1,3-dialkyl(Me, ⁱPr, ^tBu)imidazol-2-ylidene NHCs on the LPP of three classes of acrylic monomers, including linear methyl methacrylate (MMA), cyclic biorenewable γ-methyl-α-methylene-γ-butyrolactone (_γMMBL), and difunctional allyl methacrylate (AMA). For MMA polymerization, IⁱPr is not only the most active (∼3× and ∼120× more active than IMe and I^tBu, respectively), but also the most effective NHC, especially under low NHC loading conditions. Kinetic results are consistent with a bimolecular, activated monomer propagation mechanism. In the case of the more reactive _γMMBL, the polymerization by NHC/B(C₆F₅)₃ in CH₂Cl₂ is extremely rapid, with all three NHCs achieving quantitative monomer conversion in 1 min and thus reaching a high turnover frequency of≥48,000 h⁻¹. The molecular weight (MW) of P_γMMBL can be tuned by adjusting the [_γMMBL]/[NHC] ratio, and thus high MW polymers with relatively narrow MW distributions can be readily synthesized (e.g., from M_n=1.41×10⁵ g mol⁻¹, Đ=1.08 to M_n=4.89×10⁵ g mol⁻¹, Đ=1.20). The LPP by NHC/B(C₆F₅)₃ is completely chemoselective, as demonstrated by the polymerization of AMA, which selectively polymerizes the conjugated vinyl group while leaving the non-conjugated vinyl group in the allyl moiety intact, thanks to its activated monomer propagation mechanism. The resulting PAMA is syndiotactic (rr=83 %), uncross-linked, and soluble in common solvents, thus suitable for further functionalization. This quantitatively chemoselective polymerization by NHC/B(C₆F₅)₃ should provide a facile, yet powerful, approach to functional acrylic polymers.     

Polymerization of [2,5-bis(trifluoromethyl)phenyl]acetylene and polymer properties

Summary [2,5-Bis(trifluoromethyl)phenyl]acetylene [BTFPA; HCCC₆H₃-2, 5-(CF₃)₂]polymerized with W, Mo, and Nb catalysts to produce methanol-insoluble polymers in high yields. The poly(BTFPA) produced by the W(CO)₆-based catalyst at 30 °C was soluble in p-(CF₃)₂C₆H₄, and had relatively high molecular weight ([]=0.352 dL/g in p-(CF₃)₂C₆H₄). The main chain of the polymer was composed of alternating double bonds, and the polymer was a dark brown solid. The temperature at which the weight loss of the polymer started was higher than 300 °C. The polymerization behavior and polymer properties for BTFPA are compared with those for phenylacetylene and [o-(trifluoromethyl)phenyl]acetylene.