Study on Ethylene-α-Olefin Copolymerization Catalyzed by the MgCl2-Supported and Low Ti-Loading Ziegler–Natta Catalyst

Ethylene-α-olefins copolymers were synthesized with MgCl₂-supported and low Ti-loading Ziegler-Natta catalyst prepared using the one-pot balling method. The effects of the type of comonomer, the concentration of comonomer, and polymerization temperature on the catalytic activity, kinetic behavior, molecular weight, and its distribution of the resultant copolymer were studied. It was found that the resultant copolymers have a wide molecular weight distribution. The formation mechanism of polymer with broadened molecular-weight distribution was also discussed using the method of fitting the molecular weight distribution (MWD) curves with multiple Flory-Schulz functions.     

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     

Synthesis and characterization of ethylene-1-hexene copolymers using homogeneous Ziegler-Natta catalysts

Summary This study investigated the copolymerization of ethylene with 1-hexene using the homogeneous Et[Ind]₂ZrCl₂ and [Ind]₂ZrCl₂ catalysts. The Et[Ind]₂ZrCl₂ catalyst gave a higher catalytic activity than the [Ind]₂ZrCl₂ and also showed a better incorporation of 1-hexene for the same comonomer concentration in the feed. Thermal analysis (DSC) and viscosity measurements showed that an increase of the 1-hexene incorporated in the copolymer results in a decrease of the melting point, crystallinity and molecular weight of the polymer formed. The reactivity ratios for ethylene and 1-hexene confirmed the more successful incorporation of the comonomer for the polymerization catalyzed by Et[Ind]₂ZrCl₂.     

Study of the effect of the monomer pressure on the copolymerization of ethylene with 1-hexene

The effect of ethylene pressure on the copolymerization of ethylene with 1-hexene was studied. The results show an increasing of productivities (g of polymer/n_Zr h) with pressure. This tendency was not observed for the activity (g of polymer/n_Zr h bar) that decreases when pressure is raised. When varing the pressure, the characteristics and properties of the formed copolymers are in accordance with the expectation for changes in the monomer concentration; increasing the pressure causes a decrease in comonomer incorporation. At higher ethylene pressure, the polymer is more crystalline due to less incorporation of 1-hexene and the molecular weight is higher. The density of the copolymers also decreases with comonomer incorporation into the copolymer © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2567–2574, 1997     

Ethylene/α‐olefin copolymerization using diphenylcyclopentadienyl‐phenoxytitanium dichloride/Al(iBu)3/[Ph3C][B(C6F5)4] catalyst systems

Copolymerization of ethylene with 1‐octene and 1‐octadecene using constrained geometry catalysts 2‐(3,4‐diphenylcyclopentadienyl)‐4,6‐di‐tert‐butylphenoxytitanium dichloride (1), 2‐(3,4‐diphenylcyclopentadienyl)‐6‐tert‐butylphenoxytitanium dichloride (2), 2‐(3,4‐diphenylcyclopentadienyl)‐6‐methylphenoxytitanium dichloride (3), and 2‐(3,4‐diphenylcyclopentadienyl)‐6‐phenylphenoxytitanium dichloride (4) was studied in the presence of Al(ⁱBu)₃ and [Ph₃C][B(C₆F₅)₄](TIBA/B). The effect of the catalyst structure, comonomer, and reaction conditions on the catalytic activity, comonomer incorporation, and molecular weight of the produced copolymers was also examined. The 1 /TIBA/B catalyst system exhibits high catalytic activity and produces high molecular weight copolymers. The melting temperature and the degree of crystallinity of the copolymers show a decrease with the increase in the comonomer incorporation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ethylene/1-olefin copolymerization behaviour of vanadium and titanium complexes bearing salen-type ligand

Ethylene/1-olefin copolymerization using vanadium and titanium complexes bearing tetradentate [O,N,N,O]-type ligand and EtAlCl₂ or MAO as a cocatalyst is carried out. In the presence of the vanadium complex activated with EtAlCl₂ is observed (a) negative “comonomer effect”, (b) high comonomer incorporation and narrow chemical composition distribution (CCD), (c) unexpected copolymer microstructure, and (d) increased molecular weight of copolymers when compared with the homopolymer. In contrast, titanium catalyst gives copolymers with lower 1-olefin content and broad CCD. Supported complexes show higher activity, lower 1-olefins incorporation and give copolymers with ultra high molecular weights.     

Synthesis and properties coming from the copolymerization of propene with α-olefins using different metallocene catalysts

Copolymerization of propene with two α-olefins (1-hexene and 1-octadecene) using iso- and syndioselective metallocene catalysts (EtInd₂ZrCl₂, Et(2-MeInd)₂ZrCl₂, Me₂SiInd₂ZrCl₂, Ph₂CFluCpZrCl₂ and Me₂CFluCpZrCl₂) activated with methylaluminoxane (MAO) is reported. The so-called comonomer effect was seen in the catalytic activity of the Me₂SiInd₂ZrCl₂/MAO system. Incorporation of syndiotactic copolymers was greater than that of isotactic copolymers. The molecular weight of the isotactic copolymers was not affected significantly by the presence of the comonomer, but the molecular weights of the copolymers obtained with the syndioselective catalysts decreased with increasing comonomer concentration in the medium. Tensile properties were studied. Syndiotactic copolymers with incorporation of the order of 6 mol% of 1-octadecene presented elastomeric properties.     

Controlled radical alternating copolymerization of N‐phenyl maleimide with ethyl α‐ethylacrylate by reversible addition fragmentation chain‐transfer process

The alternating copolymerization of N‐phenyl maleimide (NPMI) with ethyl α‐ethylacrylate (EEA) by the reversible addition fragmentation chain‐transfer process was investigated. The monomer reactivity ratios were measured and r₁ = 0.19 ± 0.03 for NPMI and r₂ = 0.20 ± 0.04 for EEA. It was found that before about 45% of the comonomer conversion, the molecular weight of the copolymer increased with the conversion, the molecular weight distribution was rather narrow, and the molecular weight of the copolymer approached a constant value, irrespective of the length of the polymerization time. Electronic spin resonance determined that the radical signal disappeared quickly after the conversion of comonomer exceeded 45%, which may be attributed to the coupling termination of the propagating polymer chains with the EEA end with the intermediate radicals when the concentration of comonomers decreased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2376–2382, 2004     

Synthesis of linear low density polyethylene with a nano-sized silica supported Cp2ZrCl2/MAO catalyst

A nano-sized silica supported Cp₂ZrCl₂/MAO catalyst was used to catalyze the copolymerization of ethylene/1-hexene and ethylene/1-octene to produce linear low-density polyethylene (LLDPE) in a batch reactor. Under identical reaction conditions, the nano-sized catalyst exhibited significantly higher polymerization activity, and produced copolymer with greater molecular weight and smaller polydispersity index than a corresponding micro-sized catalyst, which was ascribed to the much lower internal diffusion resistance of the nano-sized catalyst. Copolymer density decreased with the increase of polymerization temperature, probably due to the decrease of reactivity ratio r ₁ and ethylene solubility with increasing temperature. Polymerization activity of the nano-sized catalyst increased rapidly with increasing comonomer concentration. Ethylene/1-octene exhibited higher polymerization activity and had a stronger comonomer effect than ethylene/1-hexene.     

Graft Copolymers of Polypropylene Films. 1. Radiation-induced Grafting of Mixed Monomers

Radiation graft copolymerization of comonomer mixtures of acrylic acid (AAc) and styrene (S) onto polypropylene (PP) films by the mutual method has been investigated. The effect of different factors that may affect the grafting yield, such as inhibitor concentration (Mohr’s salt), solvent composition (MeOH and H₂O), radiation dose and dose rate, was studied. It was found that Mohr’s salt was very effective when the content of AAc in the comonomer mixtures was low. However, the addition of 1·25wt% of Mohr’s salt reduced homopolymer formation and enhanced the grafting process. Graft copolymerization in the presence of a solvent mixture composed of methanol and water was found to afford a higher grafting yield than in pure methanol, regardless of the composition of the comonomer mixture used. However, the highest degree of grafting was obtained at a solvent composition of 20% H₂O: 80% MeOH and a comonomer mixture of 20% AAc: 80% S. An attempt was made to determine each PAAc and PS fraction by different methods in the graft copolymer obtained. Elemental analysis indicated that the PAAc fraction with respect to PS in the graft copolymer decreased with increasing AAc ratio in the comonomer feed solution. The rough assessment of these fractions by IR spectroscopy showed similar trends. The reactivity ratios of AAc and S monomers determined in the present graft copolymerization system were found to be 0·45 and 1·3, respectively. © of SCI.     

Catalytic Behavior of Bis(Pyrrolide-Imine) and Bis(Phenoxy-Imine) Titanium Complexes for the Copolymerization of Ethylene with Propylene, 1-Hexene,or Norbornene

This contribution reports the catalytic behavior of bis(pyrrolide-imine)Ti complexes 1 and 2 , [2-(RNCH)-C₄H₃N]₂TiCl₂ ( 1 , R = Ph; 2 , R = cyclohexyl), and bis(phenoxy-imine)Ti complex 3 , [2-(Ph-NCH)-3-t Bu-C₆H₃O]₂TiCl₂ for the copolymerization of ethylene with propylene, 1-hexene, or norbornene. An inspection of the X-ray structures of complexes 1–3 suggested that complexes 1 and 2 with pyrrolide-imine ligands would provide more space for olefin polymerization than complex 3 with phenoxy-imine ligands. In addition, DFT calculations also showed that active species derived from complexes 1 and 2 possess higher electrophilicity of the Ti center compared to that from complex 3 . Complexes 1 and 2 on activation with methylalumoxane (MAO) had higher affinity for propylene and 1-hexene and incorporated higher amounts of propylene ( 1 ; 30.5 mol%, 2 ; 23.4 mol%) and 1-hexene ( 1 ; 1.9 mol%, 2 ; 1.7 mol%) than complex 3 (propylene; 4.5 mol%, 1-hexene; 0.4 mol%). The incorporation levels of propylene and 1-hexene displayed by complexes 1 and 2 were lower than those for Cp₂TiCl₂ (propylene; 41.6 mol%, 1-hexene; 5.1 mol%) under identical conditions. In contrast, complexes 1 and 2 exhibited higher incorporation ability for norbornene and produced copolymers with much higher norbornene contents ( 1 ; 32.0 mol%, 2 ; 26.5 mol%) than Cp₂TiCl₂ (1.2 mol%) under the same conditions. Additionally, complex 3 also promoted higher norbornene incorporation (4.3 mol%) than Cp₂TiCl₂ and provided a copolymer with extremely narrow molecular weight distribution (M_w/M_n 1.14). A correlation exists between electrophilicity of the Ti center in active species and norbornene incorporation.     

Molecular weight distribution of polyacrylonitrile produced in supercritical CO2

An effectively linear molecular weight calibration curve of polyacrylonitrile (PAN) was obtained using a copolymer standard with a single broad molecular weight distribution. The molecular weights and molecular weight distributions of PAN obtained from precipitation polymerization of acrylonitrile in supercritical CO₂ were quantitated by the calibration curve. The effects of monomer concentration, initiator concentration, the CO₂ pressure, and the total reaction time on the molecular weight and molecular weight distribution were studied in detail. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2338–2341, 2002     

With different structure ligands heterogeneous Ziegler-Natta catalysts for the preparation of copolymer of ethylene and 1-octene with high comonomer incorporation

Comparison with the conventional Ziegler-Natta catalyst TiCl₄/MgCl₂ (I), the modified supported Ziegler-Natta catalysts (iso-PentylO)TiCl₃/MgCl₂ (II) and (BzO)TiCl₃/MgCl₂ (III) were prepared as efficient catalysts for copolymerization of ethylene with 1-octene. The complexes (II) and (III) were desirable for the production of random ethylene/1-octene copolymers coupled with higher molecular weight, higher comonomer incorporation within copolymer chain and good yield even at high temperature 80 ^°C and fairly low Al/Ti molar ratio of 100. The effects of catalysts ligands, Al/Ti molar ratio, polymerization temperature, as well as concentration of 1-octene on the catalytic activity, molecular weight and microstructure of the copolymer were investigated in detail. The structure and properties of the copolymers were characterized with ¹³C NMR, GPC, DSC and WAXD. The kinetic results also indicate that these catalysts (II) and (III) show higher catalytic activity and the produced polymers feature higher molecular weight, because of lower ratio of K_trm/K_p and K_tra/K_p, and higher ratio of K_tra/K_trm which indicates that chain transfer to cocatalyst is predominant.     

Effect of comonomer on the viscoelastic behavior of co-poly (acrylonitrile) solutions

Three copolymers of acrylonitrile-methacrylic acid [P(AN-co-MAA)], acrylonitrile-ammonium salt of methacrylic acid [P(AN-co-AMA)], acrylonitrile-methacrylamide-itaconic acid [P(AN-MAM-IA)] and PAN homopolymer were synthesized by aqueous dispersion polymerization technique. The polymerization conditions were adjusted in such a way to produce polymers with similar composition and molecular weight. The influence of comonomer nature on the viscoelastic behavior and spinnability of copolymer/dimethylsulfoxide (DMSO) solutions were investigated. It was found that incorporation of these comonomers into PAN chains led to intense decrease in zero-shear viscosity to lower value as well as appearance of distinct plateau in comparison with PAN homopolymer. However, comparing the results of complex viscosity and shear viscosity of each PAN polymer showed different shear-thinning behavior, typical deviation from Cox-Merz rule at high deformation rates. Amongst these copolymer solutions, P(AN-co-AMA) exhibited the longest relaxation time (λ) at low and medium frequencies. The lower values of frequency dependence of G′ (n′) and cross over frequency (ω_c) of storage modulus (G′) and loss modulus (G″) indicated that P(AN-co-AMA) was more elastic than other PAN copolymer solutions. The log-log plots of tan δ versus ω demonstrated that the comonomer nature affects the sol-gel transition behavior and elastic character of copolymer solutions. On average, based upon the slope of logG? versus logG? data, the incorporation of comonomers inside PAN chains led to ~50 % increase in the homogeneity of solutions compared to PAN homopolymer.     

Ethylene/α‐olefin copolymerization by nonbridged (cyclopentadienyl)(aryloxy)titanium(IV) dichloride/AliBu3/Ph3CB(C6F5)4 catalyst systems

A series of nonbridged (cyclopentadienyl) (aryloxy)titanium(IV) complexes of the type, (η⁵‐Cp′)(OAr)TiCl₂ [OAr = O‐2,4,6‐^tBu₃C₆H₂ and Cp′ = Me₅C₅ ( 1 ), Me₄PhC₅ ( 2 ), and 1,2‐Ph₂‐4‐MeC₅H₂ ( 3 )], were prepared and used for the copolymerization of ethylene with α‐olefins (e.g., 1‐hexene, 1‐octene, and 1‐octadecene) in presence of AlⁱBu₃ and Ph₃CB(C₆F₅)₄ (TIBA/B). The effect of the catalyst structure, comonomer, and reaction conditions on the catalytic activity, comonomer incorporation, and molecular weight of the produced copolymers was examined. The substituents on the cyclopentadienyl group of the ligand in 1 – 3 play an important role in the catalytic activity and comonomer incorporation. The 1 /TIBA/B catalyst system exhibits the highest catalytic activity, while the 3 /TIBA/B catalyst system yields copolymers with the highest comonomer incorporation under the same conditions. The reactivity ratio product values are smaller than those by ordinary metallocene type, which indicates that the copolymerization of ethylene with 1‐hexene, 1‐octene, and 1‐octadecene by the 1–3/ TIBA/B catalyst systems does not proceed in a random manner. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Copolymerization of ethylene/α‐olefins using bis(2‐phenylindenyl)zirconium dichloride metallocene catalyst: structural study of comonomer distribution

Catalysts have a major role in the polymerization of olefins and exert their influence in three ways: (1) polymerization behaviour, including polymerization activity and kinetics; (2) polymer particle morphology, including bulk density, particle size, particle size distribution and particle shape; and (3) polymer microstructure, including molecular weight regulation, chemical composition distribution and short‐ and long‐chain branching. By tailoring the catalyst structure, such as the creation of a bridge or introducing a substituent on the ligand, metallocene catalysts can play a major role in the achievement of desirable properties. Kinetic profiles of the metallocene catalyst used in this study showed decay‐type behaviour for copolymerization of ethylene/α‐olefins. It was observed that increasing the comonomer ratio in the feedstock affected physical properties such as reducing the melting temperature, crystallinity, density and molecular weight of the copolymers. It was also observed that the heterogeneity of the chemical composition distribution and the physical properties were enhanced as the comonomer molecular weight was increased. In particular, 2‐phenyl substitution on the indenyl ring reduced somewhat the melting point of the copolymers. In addition, the copolymer produced using bis(2‐phenylindenyl)zirconium dichloride (bis(2‐PhInd)ZrCl₂) catalyst exhibited a narrower distribution of lamellae (0.3–0.9 nm) than the polymer produced using bisindenylzirconium dichloride catalyst (0.5–3.6 nm). The results obtained indicate that the bis(2‐PhInd)ZrCl₂ catalyst showed a good comonomer incorporation ability. The heterogeneity of the chemical composition distribution and the physical properties were influenced by the type of comonomer and type of substituent in the catalyst. Copyright © 2010 Society of Chemical Industry     

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     

Investigation of the effect of branched structure on the performances of the copolymers synthesized from ethylene and α-olefin with rac-Et(Ind)2ZrCl2/MMAO catalyst system

The branched copolymers prepared from ethylene and α-olefins using rac-Et(Ind)₂ZrCl₂/MMAO catalyst system were studied. Both the absolute molecular weight and the molecular size (radius of gyration, R_g) of the polymers eluting from gel permeation chromatography (GPC) columns were obtained simultaneously via a high temperature GPC coupled with a two-angle laser light scattering (TALLS) detector. The branched structures and performances of the copolymers display approximate molecular weight and molecular sizes were investigated. Wide angle X-ray diffraction analyses indicate that 16-carbon side branch could co-crystallize effectively with backbone chain at low α-olefin incorporation. The melt behaviors of the copolymers were studied by dynamic rheological measurements. Both branch length and comonomer content affect considerably the loss modulus, storage modulus and complex viscosity of the copolymers. The relationship between the dynamic-mechanical behavior and the comonomer content of the copolymers was also examined by dynamic-mechanical experiments. It is found that the intensity of β-transition raise with comonomer content increasing.     

Chemical composition distribution study in ethylene/1‐hexene copolymerization to produce LLDPE material using MgCl2‐TiCl4‐based Ziegler‐Natta catalysts

The characteristic features of LLDPE polymerization with ZN catalyst are the time drift effect during polymerization and the bending effect when trying to decrease density of the copolymer by adding more comonomer to the polymerization. The time drift in LLDPE polymerization is revealed by a constant decrease of comonomer incorporation during polymerization time. The bending is revealed by difficulties in lowering the density of LLDPE material below the density of 920 kg/m³. With increasing comonomer content during polymerization, the density does not decrease, but the soluble fraction increases. To try to observe if these phenomena are connected, two types of catalysts, SiO₂ supported and precipitated MgCl₂ ZN catalysts, were studied. A short time (10 min) and an extended time (60 min) copolymerization test series where the polymerizations were performed in the presence of a gradually increasing comonomer amount. Both catalysts show a strong bending when density is presented as a function of 1‐hexene both in 10‐ and 60‐min polymerization, indicating no connection between time drift and bending. The density, melting point, and crystallinity results all indicate that both catalysts are making similar copolymer material with identical chemical composition distribution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Nonisothermal crystallization of metallocene propylene–decene‐1 copolymers

The nonisothermal crystallization behavior of one metallocene‐based isotactic polypropylene and three propylene–decene‐1 copolymers was studied. The effects of comonomer content and cooling rate were investigated. It was found that comonomer units enchained systematically reduce the crystallization temperature (T_c), melting temperature (T_m), fusion enthalpy (ΔH_f), and crystallinity (X_c). Such an effect becomes more evident at a faster cooling rate. With increasing comonomer content, the supercooling required for crystallization increases and the overall crystallization rate is reduced. The Avrami equation is applicable to describe the nonisothermal crystallization kinetics of propylene–decene‐1 copolymer. It was shown that, although the reduced crystallization rate constant Z_c increases with comonomer content, the Avrami exponent decreases with comonomer content and cooling rate, leading to the smaller overall crystallization rate and larger crystallization half‐time of the copolymer with higher comonomer content. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1724–1730, 2004