Copolymerization of ethylene and 1‐decene by metallocenes: Direct comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2

Copolymerizations of ethylene with 1‐decene have been carried out by using two syndiospecific metallocenes synthesized by modifying the bridge: highly syndiospecific isopropylidene(1‐η⁵‐cyclopentadienyl)(1‐η⁵‐fluorenyl)‐dimethylzirconium (Me₂C(Cp)(Flu)ZrMe₂, 1 ) and less syndiospecific (1‐fluorenyl‐2‐cyclopentadienylethane)‐dimethylzirconium (Et(Cp)(Flu)ZrMe₂, 2 ), in the presence of [Ph₃C][B(C₆F₅)₄] as a cocatalyst. The ethano bridged 2 compound of smaller dihedral angle showed much higher activity than 1 compound. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1‐decene comonomer is present in the feed. The compound 1 showed better comonomer reactivity than 2 . The properties (T_m, density, and crystallinity) of copolymers seem not to be affected by the type of bridge of the metallocenes, and mainly depend on 1‐decene content in the copolymer.     

Modified syndiotactic polypropene: Poly(propene-co-octene) and blends with atactic oligopropene

Propene and 1-octene were copolymerized with the syndiospecific homogeneous metallocene catalyst Me₂C(Cp)(Flu)ZrCl₂/MAO. Large amounts of octene were incorporated randomly. While catalyst activity was not affected markedly by low octene content, molecular weight, crystallinity, Young's modulus, and glass transition temperature were reduced with increasing octene content. Blends of atactic oligopropene with syndiotactic polypropene and poly(propene-co-octene) were prepared from toluene solution and compared with a reactor blend prepared with a hybrid catalyst containing a mixture of syndiospecific Me₂C(Cp)(Flu)ZrCl₂/MAO and non-specific Cp₂ZrCl₂/MAO. Atactic oligopropene acted as plasticizer reducing Young's modulus and glass transition temperature of the blends.     

Propylene polymerization using combined syndio‐ and isospecific metallocene catalysts supported on silica/MAO

Syndiotactic and isotactic polypropylene were produced using the metallocene compounds Ph₂C(Flu)(Cp)ZrCl₂ and SiMe₂(2‐Me,4‐Ph‐Ind)₂ZrCl₂ in homogeneous system and supported on silica/MAO. These catalysts were evaluated either isolated or as a binary system. In the latter case, the iso‐ and syndiospecific metallocene complexes were immobilized together during the preparation of the supported catalyst. In a further experimental set, the syndio‐ and isospecific isolated heterogeneous catalysts were mixed at the moment of propylene polymerization. The polypropylenes obtained were evaluated using differential scanning calorimetry. The catalytic activities were also investigated. At all the studied polymerization temperatures, the results showed that the binary catalyst produced polypropylenes with lower melting temperatures in comparison with those obtained when the mixture of isolated supported syndio‐ and isospecific catalysts was employed. Moreover, the activation energies for the polymerization of all catalysts systems were calculated, resulting in a lower value for the binary system when compared to that employing the catalyst mixture and to both the isolated supported metallocene catalysts. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 628–637, 2006     

Homopolymerization of Higher 1‐Olefins with Metallocene/MAO Catalysts

Linear 1‐olefins from 1‐pentene to 1‐octadecene are polymerized by non‐stereospecific Cp₂HfCl₂ ( 1 ), syndiospecific Me₂C(Cp)(9‐fluorenyl)ZrCl₂ ( 2 ) and isospecific Et(Ind)₂ZrCl₂ ( 3 ) catalysts in the presence of MAO. The molecular weight of the resulting polymers (GPC) is highly dependent on the nature of the catalyst, but more or less independent of the monomer chain length. The stereoregularity of the poly(1‐olefins) obtained with 2 and 3 as determined by NMR spectroscopy decreases linearly with increasing monomer chain length. A decrease in isotacticity occurs for the poly(1‐olefins) synthesized with 3 when increasing the catalyst concentration. Vinylidene, 1,2‐disubstituted and 1,1,2‐trisubstituted double bonds attributed to different chain termination mechanisms are generated during the polymerization processes.     

Crystallization analysis fractionation of ethene/1-hexene copolymers made with the MAO-activated dual-site (1,2,4-Me3Cp)2ZrCl2 and (Me5Cp)2ZrCl2 system

Different poly(ethene-co-1-hexene) samples with varying amounts of 1-hexene were characterized by crystallization analysis fractionation (Crystaf). The samples were synthesized with (1,2,4-Me₃Cp)₂ZrCl₂, (Me₅Cp)₂ZrCl₂, and a mixture of these two catalysts in a 1:1 molar ratio. In addition, preparative Crystaf was used to fractionate some of the samples made with the catalyst mixture into 1-hexene-rich and 1-hexene-poor fractions. These fractions were characterized by Crystaf, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC), and compared with copolymers made under similar conditions using the individual catalysts. Both (1,2,4-Me₃Cp)₂ZrCl₂ and (Me₅Cp)₂ZrCl₂ produced copolymers with unimodal distribution of short chain branches (SCBD), as expected for single-site catalysts. The catalyst mixture produced copolymers with bimodal SCBDs when 0.38 mol/l or higher concentrations of 1-hexene were used. The high temperature peak results from crystallization of polymer chains with few comonomer units, and these are attributed to (Me₅Cp)₂ZrCl₂. The low temperature peak results from crystallization of polymer chains made by (1,2,4-Me₃Cp)₂ZrCl₂, and these chains contain many comonomer units. Direct evidence for relative activity enhancement of the (Me₅Cp)₂ZrCl₂ catalyst in the dual-site system was observed.     

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.     

Quarterpolymerizations of Ethene/Propene/Hexene/ Ethylidenenorbornene and Ethene/Propene/Octene/ Ethylidenenorbornene with [Me2C(3-MeCp)(Flu)]ZrCl2 / MAO

Summary Quarterpolymerizations of ethene/propene/hexene/ethylidenenorbornene and ethene/propene/octene/ethylidenenorbornene were carried out using the catalytic system [Me₂C(3-MeCp)(Flu)]ZrCl₂ / MAO to determine whether it is possible to lower the glass transition temperature of an EPDM. The influence of the quartermonomer on the polymerization activity and on the product properties, such as the incorporation rates of the three other monomers, the molar mass and molar mass distribution of the polymer were looked at. It was found that the activity is decreased using 1-hexene on the one hand and 1-octene on the other hand as quartermonomer with the effect being more distinct using the former. Both 1-hexene and 1-octene are incorporated to the detriment of propene and ENB, the reduction of the ENB content being more distinct. The molar masses of the polymers are not affected by the substitution of these two monomers by the quartermonomer. The glass transition temperature, however, using 1-hexene or 1-octene, was reduced - in the case of the latter by more than 10 °C from −50 to −62 °C. Received: 10 May 2000/Revised version: 19 October 2000/Accepted: 27 November 2000     

Study of the polymerization of 1-octadecene with different rnetallocene catalysts

Summary 1-Octadecene (C18) was polymerized by using different metallocene catalysts. The rac-Et(Ind)₂ZrC1₂/MAO (I) and rac-Me₂Si(Ind)₂ZrC1₂/MAO (III) presented the highest activity as compared with ra-Et(2-Me-Ind)₂ZrCl₂/MAO (II) and Ph₂C(Flu)(Cp)ZrC1₂/MAO (IV) catalysts. Catalyst IV produced polymers with highest molecular weights. The microstructure of the polymers was determined by ¹³C-NMR spectroscopy. Catalyst systems I, II and III produced isotactic polymers while catalyst IV produced polymers with mainly syndiotactic structures but with large amount of stereoregular error. Received: 21 June 2002/Revised version: 4 November 2002/ Accepted: 4 November 2002     

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.     

Copolymerization of ethylene and 1-octene by homogeneous and different supported metallocenic catalysts

In this work, the performance of the homogeneous catalyst system based on Et(Flu)₂ZrCl₂/MAO was evaluated on the copolymerization of ethylene and 1-octene. Characteristics of some of the produced polymers were also investigated. A study was performed to compare this system with that of Cp₂ZrCl₂/MAO. The influence of different support materials for the Cp₂ZrCl₂ was also evaluated, using silica, MgCl₂, and the zeolite sodic mordenite NaM. An increase in activity was observed in relation to the comonomer addition for the two homogeneous catalysts. The copolymers produced by the Et(Flu)₂ZrCl₂/MAO system showed higher molecular weight and narrower molecular weight distribution. We verified that the catalyst supported on SiO₂ was the most active one, although the copolymers produced with the catalyst supported on NaM showed higher molecular weight and lower molecular weight distribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 724–730, 2001     

The effect of the ethylene pressure on its reaction with 1-hexene, 1-octene and 4-methyl-1-pentene

Summary Copolymers of ethylene and 1-hexexe, 1-octene and 4-methyl-1-pentene were obtained using Et[In]₂ZrCl₂/MAO catalyst at various pressures. The increase of 1-hexene and 1-octene concentration in the feed increases catalyst activity(g/nZr.h.bar) and productivity(g/nZr.h). For 4-methyl-1-pentene the activity is independent on comonomer concentration. Increasing the ethylene pressure the productivity of the copolymerization increases and the activity shows a weak decay. Characterization of the copolymer shows that at higher pressure the cristallinity of the copolymers is higher due to lower comonomer incorporation. There is a good linear correlation of cristallinity with comonomer concentration in the feed for 1-hexene and 1-octene at a fixed pressure, but not for 4-methyl-1-pentene.     

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.     

Polymerization of ethylene: Some aspects of metallocene catalyst stabilization under homogeneous and heterogeneous reaction conditions

The development of metallocene‐based catalysts is an important advance on the study of polyolefinic materials. However, due to the rather different conditions that are established in actual applications, only around 3% of these polymers are obtained from metallocene technology. In view of this, novel strategies must be developed to produce metallocene‐based catalysts that are more thermally stable, which is a fundamental requirement to establish metallocene technologies. Homogeneous and heterogeneous polymerizations of ethylene were compared, using the Ph₂C(Cp)(Flu)ZrCl₂/MAO system. Homogeneous polymerizations were more active than the corresponding supported reactions. At low ethylene pressure, the addition of 1‐hexene increases the activity under homogeneous conditions. Nevertheless, this is not observed on the respective supported systems. At higher pressure conditions, all polymerizations attained higher yields. However, when the reaction temperature increases the activity significantly decreases under homogeneous conditions. Furthermore, when the polymerization was performed under heterogeneous conditions the deactivation was lower. The homogeneous and supported catalytic systems show different characteristics and, in all attempted reactions, immobilization of the molecular catalyst reduces the activity. However, the deactivation ratio was lower when the polymerization was performed under heterogeneous conditions. This means that immobilization of Ph₂C(Cp)(Flu)ZrCl₂ on silica can improve the thermal stability of the catalytic species. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Syndioselective propylene polymerization: Comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2

The kinetics and stereochemical control of propylene polymerization initiated by syndiospecific isopropylidene(1-η⁵-cyclopentadienyl)(1-η⁵-fluorenyl)-dimethylzirconium–methyl aluminoxane (1/MAO) and (1-fluorenyl-2-cyclopentadienylethane)-dimethylzirconium–MAO (2/MAO) were investigated. The influence of MAO concentration and polymerization temperature (T_p) on polymerization kinetics and polypropylene properties, such as molecular weight, molecular weight distribution (MWD), and stereoselectivity, have been studied in detail. The activity of both catalytic systems is very sensitive to the concentration of MAO. The 1/MAO and 2/MAO catalysts record maximum activity when [Al]/[Zr] ratio is around 1300 and 2500, respectively. The activity and the degree of stereochemical control are also sensitive to T_p. The 2/MAO catalyst is much more thermally stable than 1/MAO catalyst; the former shows maximum activity at 80°C, whereas the latter shows maximum activity at 20°C. The cationic active species generated by 2/MAO is not so stereorigid as those by 1/MAO so that 2/MAO catalyst produces sPP of broad MWD (4.43–6.38) and low syndiospecificity at high T_p. When T_p is above 50°C, 2/MAO catalyst produces completely atactic polypropylene. The results of fractionation of sPP samples produced by 1/MAO and 2/MAO demonstrate that 1/MAO catalyst is characterized by uniform active sites, but 2/MAO is characterized by multiple active sites. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 973–983, 1998     

Polymerization of vinyl chloride with butyllithiums and metallocene catalysts

Polymerizations of vinyl chloride (VC) with butyllithium (BuLi) and metallocene catalysts were investigated. In the polymerization of VC with BuLi, the activity for polymerization decreased in the following order; t‐BuLi > n‐BuLi > s‐BuLi. A polymer controlled structurally in the main chain was found to be synthesized from the polymerization of VC with BuLi. The molecular weights of polymers obtained in bulk polymerization were higher than those of polymers obtained in solution. A linear relationship of the M_n of the polymer and the polymer yields was observed. The M_w/M_n of the polymer did not change significantly during polymerization, although the M_w/M_n was around 2. Thermal stability of the polymer obtained with BuLi was higher than that of polymer obtained with radical initiators, as determined by TGA measurements. In the polymerization of VC with Cp*TiX₃/MAO (X: Cl and OCH₃) catalysts, polymers were obtained with both catalysts, although the rate of polymerization was slow. The Cp*Ti(OCH₃)₃//MAO catalyst in CH₂Cl₂ gave higher‐molecular‐weight polymers in a better yield than in toluene. From elemental analysis and the NMR spectra of the polymers, the Cp*Ti(OCH₃)₃/MAO catalyst gave polymers consisting of repeating regular head‐to‐tail units, in contrast to the Cp*TiCl₃/MAO catalyst, which gave polymers having anomalous units.     

Copolymerization of ethylene and norbornene by zirconium complexes containing symmetrically tuned trianionic ligands

Homo and copolymerization of ethylene and cyclic olefins were carried out using C ₃ symmetric N[CH₂CH(Ph)O]₃ZrCl (1-ZrCl) and also pseudo-C _s symmetric N[CH₂CH(Ph)O]₃ZrCl (2-ZrCl) catalyst systems upon activation with MAO. Incorporation of comonomer into the polyethylene back bone was mainly governed by catalyst symmetry. Norbornene (NB) incorporation was as high as 40% in the ethylene–norbornene copolymer (ENC) using C ₃ symmetric 1-ZrCl/MAO catalyst system and 25% in the case of the pseudo-C _s symmetric analogue 2-ZrCl. Unlike the more efficient titanium analogues, the copolymerization of ethylene and NB showed a marginal decrease in catalyst activity and NB incorporation on switching over to the Zr analogues. The aluminum to metal ratio required for catalyst activation was higher for the Zr catalysts compared to that of its Ti analogues. ¹³C NMR spectral studies on the copolymer clearly indicated the incorporation of NB in an alternating manner.     

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     

Synthesis and functionalization of poly(ethylene‐co‐dicyclopentadiene)

Copolymerizations of ethylene with endo‐dicyclopentadiene (DCP) were performed by using Cp₂ZrCl₂ (Cp = Cyclopentadienyl), Et(Ind)₂ZrCl₂ (Ind = Indenyl), and Ph₂C(Cp)(Flu)ZrCl₂ (Flu = Fluorenyl) combined with MAO as cocatalyst. Among these three metallocenes, Et(Ind)₂ZrCl₂ showed the highest catalyst performance for the copolymerization. From ¹H‐NMR analysis, it was found that DCP was copolymerized through enchainment of norbornene rings. The copolymer was then epoxidated by reacting with m‐chloroperbenzoic acid. ¹³C‐NMR spectrum of the resulting copolymer indicated the quantitative conversion of olefinic to epoxy groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 103–108, 1999     

Highly active novel Ni-diimine pre-catalyst containing bis-ketimine ligand for the vinyl polymerization of norbornene

Novel Nickel-diimine pre-catalyst (1NiBr₂) containing N,N′-bis(diphenylmethylene)-ethylenediamine ligand was able to quantitatively polymerize norbornene (NBE) into polynorbornene (PNBE) at 50 °C upon activation with methylaluminoxane (MAO). The monomer concentration governs the rate of reaction and the polymer characteristics. Thermal and spectral analysis revealed the polymerization pathway to occur via vinyl addition and not ring opening. The homopolymerization of 1-hexene or ethylene could not be achieved using 1NiBr₂/MAO catalyst system, but the presence of 1-hexene did not prevent the quantitative polymerization of NBE without 1-hexene incorporation. The characteristics of the polymers formed were found to be different in terms of solubility and molecular weight compared to those of the product generated by the homopolymerization of NBE in the absence of 1-hexene. Here 1-hexene acted as a chain transferring agent and control the molecular weight of PNBEs produced.     

Study on the copolymerization of propylene with norbornene using metallocene catalysts

The copolymerization of propylene with norbornene, using the metallocene catalysts Me₂Si(2-Me-Ind)₂ZrCl₂ and Ph₂C(Flu)(Cp)ZrCl₂ was evaluated. The presence of norbornene decreases the polymerization activity in both systems. In the Me₂Si(2-Me-Ind)₂ZrCl₂ system, the decrease is ca. 80?% using 0.5?mL of norbornene while the addition of 2?mL reduces the activity by 97?%. The molecular weight of the materials decreases between 27,000 and 37,000?g/mol in the presence of norbornene. The Ph₂C(Flu)(Cp)ZrCl₂/MAO system has the same tendency, but the norbornene has a lesser effect on the activity, with 2?mL of comonomer reducing the activity ca. 80?%. The molecular weight decreased significantly with this system as well. The elongation at break of some of the materials was 80 times higher than the homopolymer and the Young’s modulus slightly superior to the homopolymer. This indicates that it is possible to generate materials that keep the properties of a syndiotactic polypropylene but with good elastomeric properties.