Polymer materials based on ethylene copolymers with substituted norbornene

The copolymers of ethylene with 5-ethylidene-2-norbornene containing 10–65% of the cyclic comonomer have been prepared with the use of three ansa-metallocene catalysts, namely, Et[Ind]₂ZrCl₂-methylaluminoxane, Et[IndH₄]₂ZrCl₂-methylaluminoxane, and Me₂Si[Ind]₂ZrCl₂-methylaluminoxane. Side groups >C=CH-CH₃ capable of participation in the ozonolysis reaction have been incorporated into polymer chains via the copolymerization of ethylene with the cyclic comonomer. As evidenced by DSC, and X-ray diffraction, and very cold neutron scattering measurements of the supramolecular structure of the copolymers, the enrichment of the copolymer with the cyclic comonomer causes transformation of the ethylene-5-ethylidene-2-norbornene copolymer from the semicrystalline state to the amorphous state. This effect is accompanied by an increase in the density and optical transparency of the material and a rise in its glass transition temperature. Among the copolymers under study, the highest T _g (83°C) is exhibited by the copolymer synthesized with the Et[Ind]₂ZrCl₂-methylaluminoxane catalyst and containing 30 mol % 5-ethylidene-2-norbornene.     

Studies on the Synthesis of Ethylene Copolymers and Their Properties

The copolymerization of ethylene and 5-ethylidene-2-norbornene (ENB) catalyzed by metallocene catalysts system is reported in this paper. The catalysts include Et(Ind)₂ ZrCl₂/MAO and Cp₂ZrCl₂/MAO. The resulting copolymer contains an ethylidene group which can be readily converted to a hydroxyl group by hydrogen borane. Then the hydroxyl group in turn can be utilized for grafting with ?-caprolactone. The dependence of the graft weight percentage on the reaction time was also studied. The graft copolymer is a compatibilizer for various polyethylene blends with engineering plastics. A functional polyethylene can be easily synthesized by the copolymerization of ethylene and 9-decen-l-ol using a homogeneous catalytic system of El(Ind)₂ZrCl₂/MAO. The resulting functional polyethylene was characterized by NMR, DSC, IR and TGA; and can also be utilized for grafting with ?-caprolactone. The grafted copolymer is also an effective compatibilizer.     

Influences of methylaluminoxane separated by porous inorganic materials on the isospecific polymerization of propylene

Inorganic siliceous porous materials such as MFI type zeolite, mesoporous silica MCM‐41 and silica gel with different average pore diameters were applied to the adsorptive separation of methylaluminoxane (MAO) used as a cocatalyst in α‐olefin polymerizations. The separated MAOs combined with rac‐ethylene‐(bisindenyl)zirconium dichloride (rac‐Et(Ind)₂ZrCl₂) were introduced to propylene polymerization, and their influences on the polymerization activity and stereoregularity of the resulting polymers were investigated. The polymerization activity and isotactic [mmmm] pentad of the produced propylene were markedly dependent upon the pore size of the porous material used for adsorptive separation. From the results obtained from solvent extraction of the produced polymers, it was suggested that there are at least two kinds of active species with different stereospecificity in the rac‐Et(Ind)₂ZrCl₂/MAO catalyst system.     

Renewable chain transfer agents for metallocene polymerizations: The effects of chiral monoterpenes on the polyolefin molecular weight and isotacticity

Monoterpenes were used as renewable chain transfer agents and polymerization solvents for metallocene/methylaluminoxane (MAO) catalysis. The polymerization of 1‐hexene, ethylene, and propylene in d‐limonene, hydrogenated d‐limonene and α‐pinene is reported. As detected by ¹H NMR analysis of the alkene region, chain transfer to d‐limonene yielded a higher percentage of trisubstituted alkenes. Size exclusion chromatography detected a decrease in molecular weight values resulting from chain transfer to d‐limonene. The [mmmm] pentads for isotactic polypropylene were characterized by ¹³C NMR and FTIR spectroscopy. Propylene polymerizations with the Et(Ind)₂ZrCl₂/MAO and Me₂Si(Ind)₂ZrCl₂/MAO catalyst systems in d‐limonene gave [mmmm] pentad values as high as 0.97. For the Et(Ind)₂ZrCl₂/MAO catalyst system at 0 °C, the mol fraction of [mmmm] pentads increased from 0.86 to 0.94 upon switching the solvent from toluene to d‐limonene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3150–3165, 2007     

Combined metallocene catalysts: an efficient technique to manipulate long-chain branching frequency of polyethylene

The solution polymerization of ethylene in Isopar E in a semi-batch reactor using combined CGC-Ti and Et[Ind]₂ZrCl₂ catalysts was studied. Methylaluminoxane (MAO) and tris(pentafluorophenyl)borane were used as co-catalysts. Samples were analyzed by ¹³C NMR and gel permeation chromatography (GPC) for their branching content and molecular weight distribution. It was shown that there was an optimum ratio of CGC-Ti/Et[Ind]₂ZrCl₂ that maximizes the number of long-chain branches of the formed polyethylene.     

Copolymerization of Ethylene and Propylene Using Silicon Tetrachloride‐Modified Silica/MAO with Et[Ind]2ZrCl2 Metallocene Catalyst

For the copolymerization of ethylene with propylene or a higher α‐olefin, using Et[Ind]₂ZrCl₂ metallocene catalyst, modification of silica with silicon tetrachloride prior to MAO adsorption can increase the activity, which is more pronounced for ethylene/1‐hexene copolymerization at higher pressure and temperature. The molecular weight of the copolymer produced was lower and the polydispersity tends to be decreased. No significant effect of SiCl₄ addition on the microstructure and the chemical composition distribution of the copolymer produced was observed.     

Influence of the catalyst and polymerization conditions on the long‐chain branching of metallocene‐catalyzed polyethenes

A study was made on the effects of polymerization conditions on the long‐chain branching, molecular weight, and end‐group types of polyethene produced with the metallocene‐catalyst systems Et[Ind]₂ZrCl₂/MAO, Et[IndH₄]₂ZrCl₂/MAO, and (n‐BuCp)₂ZrCl₂/MAO. Long‐chain branching in the polyethenes, as measured by dynamic rheometry, depended heavily on the catalyst and polymerization conditions. In a semibatch flow reactor, the level of branching in the polyethenes produced with Et[Ind]₂ZrCl₂/MAO increased as the ethene concentration decreased or the polymerization time increased. The introduction of hydrogen or comonomer suppressed branching. Under similar polymerization conditions, the two other catalyst systems, (n‐BuCp)₂ZrCl₂/MAO and Et[IndH₄]₂ZrCl₂/MAO, produced linear or only slightly branched polyethene. On the basis of an end‐group analysis by FTIR and molecular weight analysis by GPC, we concluded that a chain transfer to ethene was the prevailing termination mechanism with Et[Ind]₂ZrCl₂/MAO at 80 °C in toluene. For the other catalyst systems, β‐H elimination dominated at low ethene concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 376–388, 2000     

Stereochemical control in homogeneous Ziegler-Natta catalysts

Racemic ethylenebis(η⁵-indenyl)zirconium dichloride (Et[Ind]₂ZrCl₂) activated with methylaluminoxane (MAO) catalyzed propylene polymerization with varying degree of stereochemical control which decreases greatly with the increase of T_p (temperature of polymerization). The PP&s are characterized by low melting temperature (T_m), high solubility, and prefers to crystallize in the γ-modification. The catalytic activity of Et[Ind]₂ZrCl₂/MAO becomes very small with the lowering of T_p. Very active and highly stereoselective cationic metallocene alkyl, Et[Ind]₂Zr⁺(CH₃), was produced by the reaction of Et[Ind]₂Zr(CH₃)₂ with Ph₃C⁺B(C₆F₅)₄⁻. Comparison of this system with the Et[Ind]₂ZrCl₂/MAO catalyst showed that in the latter case a quarter of the Et[Ind]₂ZrCl₂ was converted by MAO to Et[Ind]₂Zr⁺CH₃ at room temperature but less than 0.14% of the Zr was so activated at −20°C. The Et[IndH₄]ZrCl₂/MAO catalyst was shown to have two kinds of catalytic species one with high propagation rate constant (k_p) and stereoselectivity and another with low k_p and poor stereoselectivity. The very narrow molecular weight distribution of the PP produced may be attributed to the fact that the different types of active species have comparable k_p/k_tr^A, the latter is the rate constant of transfer. Non-symmetric, rac-[anti-ethylidene(1-η⁵-indenyl)(1-η⁵-tetramethylcyclopentadienyl)-Ti-Cl₂ and -(CH₃)₂ have been synthesized and structures determined. The complexes provide dissimilar steric environment to propagating chains to produce crystalline-amorphous multiblock thermoplastic elastomeric PP. The polymerization process here involves a two-state propagation mechanism.     

Effective activation of metallocene catalysts with supported‐type Ph3CClO4 in ethylene polymerization

Supported type cocatalysts using triphenylcarbenium perchlorate (Ph₃CClO₄) were prepared by impregnation on inorganic carrier, magnesium chloride (MgCl₂) and applied to ethylene polymerizations with rac‐Et[Ind]₂ZrCl₂. Homogeneous polymerizations with Ph₃CClO₄ were also carried out for comparison. The activity of homogeneous polymerization was much lower than that obtained with methylaluminoxane (MAO). On the other hand, rac‐Et[Ind]₂ZrCl₂ activated by the supported type Ph₃CClO₄/MgCl₂ system displayed high activity comparable to that obtained with MAO. From the results of fractionation and polymerization of the rac‐Et[Ind]₂ZrCl₂‐Ph₃CClO₄/MgCl₂ catalyst system, it was found that the increased activity mainly came from the active species in the supernatant part. UV‐vis spectroscopic measurements combined with ICP analysis indicate that the active species in the supernatant fraction are composed of a stoichiometric amount of perchlorate and metallocene catalyst.     

Silica-supported metallocenes: stereochemical comparison between homogeneous and heterogeneous catalysis

Propylene was polymerized in the presence of the isospecific Et(Ind)₂ZrCl₂ (Et: ethylene, Ind: indenyl) and the aspecific (Ind)₂ZrCl₂ complexes in solution and anchored to SiO₂ and SiO₂/MAO (MAO: methylaluminoxane) supports. From the stereochemical analysis of the polypropene samples obtained it can be deduced that (i) the same active species is formed when a metallocene is in solution and when it is anchored to the SiO₂/MAO support and (ii) a completely different active species is formed when the metallocene is anchored to the silica. The fact that both systems Et(Ind)₂ZrCl₂ SiO₂ and (Ind)₂ZrCl₂ SiO₂ produce the same prevailingly isospecific polymer suggests that only isospecific centers are formed in this case, independently of the metallocene stereochemical structure.     

Results coming from homogeneous and supported metallocene catalysts in the homo- and copolymerization of olefins

Ethylene, propylene and α-olefins were homo- and copolymerized in the presence of a series of homogeneous catalytic systems consisting of methylaluminoxane (MAO) and group IV metallocenes such as Et(Ind)₂ZrCl₂ (I), Me₂Si(Ind)₂ZrCl₂ (II), Et(2-Me-Ind)₂ZrCl₂ (III), Ph₂C(Flu)(Cp)ZrCl₂ (IV). It was found that the catalytic activity, the incorporation of comonomer in the case of copolymers, and the microstructure of the polymers depend on the catalyst's structure. For heterogeneous catalysts, several supports based on metal oxide compounds have been investigated, with special emphasis in those obtained by the sol-gel preparation technique. The homo- and copolymerization of the monomers in the homogeneous systems studied where also investigated using the same catalyst system, but in a heterogeneous medium. Comparative results from the homogeneous and heterogeneous systems are presented and discussed.     

The Influence of Bridge Type on the Activity of Supported Metallocene Catalysts in Ethylene Polymerization简

Ethylene polymerization was carried out by immobilization of rac-ethylenebis(1-indenyl)zirconium dichloride(Et(Ind)2 ZrCl2) and rac-dimethylsilylbis(1-indenyl)zirconium dichloride(Me2 Si(Ind)2 ZrCl2) preactivated with methylaluminoxane(MAO) on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2 Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 °C and 70 °C for Me2 Si(Ind)2 ZrCl2 /MAO and Et(Ind)2 ZrCl2 /MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 °C for both catalysts systems. The melting points of the produced polyethylene were about 130 °C, which could be attributed to the linear structure of HDPE.     

Evidence of the Quasi‐Living Character of the ansa‐Zirconocene/MAO‐Catalyzed Copolymerization of Ethylene and Norbornene

The kinetics of the ethylene‐norbornene copolymerization, catalyzed by rac‐Et(Ind)₂ZrCl₂/MAO, 90%rac/10%meso‐Et(4,7‐Me₂Ind)₂ZrCl₂/MAO and rac‐H₂C(3‐tert‐BuInd)₂ZrCl₂/MAO was followed by sampling from the reaction mixture at fixed time intervals. Catalyst activity, copolymer composition and molar mass were studied as a function of time. The polymers showed an unusually low polydispersity and a significant increase in their molar mass with time, suggesting a quasi‐living polymerization.     

Copolymerization of ethylene with allylbenzene using rac-ethylenebis(indenyl)zirconium dichloride/methylaluminoxane as a catalyst

Ethylene was copolymerized with allylbenzene using rac-ethylenebis(indenyl)zirconium dichloride (Et(Ind)₂ZrCl₂)/methylaluminoxane (MAO) as a catalyst. Analysis of the copolymers obtained revealed that chain transfer to aluminium was a preferred chain transfer reaction during the copolymerization. It seems that chain termination through aluminium transfer is induced by the allylbenzene unit incorporated in the propagating chain end. Hydroxy-terminated ethylene copolymers were obtained when the copolymer solution was exposed to air before precipitation of the polymer in acidic methanol.     

茂－茚锆金属络合物催化乙烯/1－己烯共聚和丙稀均聚研究

Complexes （R^1Cp）（R^2Ind）ZrCl2, the catalysts previously reported active for ethylene polymerization showed high activity in ethylene/1-hexene copolymerization and propylene polymerization in the presence of MAO. The content of 1-hexene in copolymers ranged from 1.2% to 3.2%. In propylene polymerization the complex 1 showed the highest activity, up to 1.2×10^6 g of polypropylene per mol of catalyst per hour. Based on the analysis of NMR spectral data, the relationships between complex structures and polymerization results were explored.     

Synthesis of Various Functional Propylene Copolymers Using rac‐Et[1‐Ind]2ZrCl2/MAO as the Catalyst System

Propylene copolymers with different polar groups were synthesised using rac‐Et[1‐Ind]₂ZrCl₂/MAO as the catalyst system. 10‐Undecen‐1‐ol, 10‐undecenoyl chloride, 10‐undecenoic acid, 2‐(9‐decen‐1‐yl)‐1,3‐oxazoline, 2‐(9‐decen‐1‐yl)‐4,4‐dimethyl‐1,3‐oxazoline, and 2‐[4‐(10‐undecene‐1‐oxy)phenyl]‐1,3‐oxazoline were used as comonomers. The addition of water to the 10‐undecenoyl chloride copolymer solution led to an acid‐functionalised copolymer. In the case of 2‐(9‐decen‐1‐yl)‐1,3‐oxazoline and its homopolymers, polymerisation temperature was varied. Up to 0.61 mol‐% comonomer were incorporated into the poly(propylene)s. The catalyst activities for 10‐undecen‐1‐ol, 10‐undecenoyl chloride and 10‐undecenoic acid were much higher than for the oxazoline comonomers.     

Shape and diffusion of the monomer‐controlled copolymerization of ethylene and α‐olefins over Cp2ZrCl2 confined in the nanospace of the supercage of NaY

Cp₂ZrCl₂ confined inside the supercage of NaY zeolites [NaY/methylaluminoxane (MAO)/Cp₂ZrCl₂] exhibited the shape and diffusion of a monomer‐controlled copolymerization mechanism that strongly depended on the molecular structure of the monomer and its size. For the ethylene–propylene copolymerization, NaY/MAO/Cp₂ZrCl₂ showed the effect of the comonomer on the increase in the polymerization rate in the presence of propylene, whereas the ethylene/1‐hexene copolymerization showed little comonomer effect, and the ethylene/1‐octene copolymerization instead showed a comonomer depression effect on the polymerization rate. Isobutylene, having a larger kinetic diameter, had little influence on the copolymerization behaviors with NaY/MAO/Cp₂ZrCl₂ for the ethylene–isobutylene copolymerization, which showed evidence of the shape and diffusion of a monomer‐controlled mechanism. The content of the comonomer in the copolymer chain prepared with NaY/MAO/Cp₂ZrCl₂ decreased by about one‐half in comparison with that of Cp₂ZrCl₂. A differential scanning calorimetry study on the melting endotherms after the successive annealing of the copolymers showed that the copolymers of NaY/MAO/Cp₂ZrCl₂ had narrow comonomer distributions, whereas those of homogeneous Cp₂ZrCl₂ were broad. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2171–2179, 2003     

Copolymerization of ethylene with bicyclo[2.2.1]hept-5-ene-2-methanol: A facile route to hydroxyl functional poly(ethylene)s

A direct and efficient route to the synthesis of hydroxyl functional polyethylene was identified by copolymerization of ethylene with bicyclo[2.2.1]hept-5-ene-2-methanol prereacted with trimethylaluminium using the catalyst system metallocene/MAO. Copolymerization studies were conducted using three metallocenes, namely, Cp₂ZrCl₂, Et(ind)₂ZrCl₂ and Me₂SiCp₂ZrCl₂ the last one of which gave a copolymer containing as much as 6.2 mol-% of alcohol. The effect of the Al/Zr ratio as well as of temperature was studied. The copolymers were characterized by means of ¹H NMR, differential scanning calorimetry, and intrinsic viscosity measurements.     

Synthesis and characterization of ethylene‐propylene‐1‐pentene terpolymers

Ethylene (E), propylene (P), and 1‐pentene (A) terpolymers differing in monomer composition ratio were produced, using the metallocenes rac‐ethylene bis(indenyl) zirconium dichloride/methylaluminoxane (rac‐Et(Ind)₂ZrCl₂/MAO), isopropyl bis(cyclopentadienyl)fluorenyl zirconium dichloride/methylaluminoxane (Me₂C(Cp)(Flu)ZrCl₂/MAO, and bis(cyclopentadienyl)zirconium dichloride, supported on silica impregnated with MAO (Cp₂ZrCl₂/MAO/SiO₂/MAO) as catalytic systems. The catalytic activities at 25 °C and normal pressure were compared. The best result was obtained with the first catalyst. A detailed study of ¹³C NMR chemical shifts, triad sequences distributions, monomer‐average sequence lengths, and reactivity ratios for the terpolymers is presented. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 947–957, 2008     

Ethylene‐Norbornene Terpolymerization with 5‐Vinyl‐2‐norbornene Using Single‐Site Catalysts

The incorporation of 5‐vinyl‐2‐norbornene (VNB) into ethylene‐norbornene copolymer was investigated with catalysts [Ph₂C(Fluo)(Cp)]ZrCl₂ ( 1 ), rac‐[Et(Ind)₂]ZrCl₂ ( 2 ), and [Me₂Si(Me₄Cp)^tBuN]TiCl₂ ( 3 ) in the presence of MAO by terpolymerizing different amounts of 5‐vinyl‐2‐norbornene with constant amounts of ethylene and norbornene at 60°C. The highest cycloolefin incorporations and highest activity in terpolymerizations were achieved with 1 . The distribution of the monomers in the terpolymer chain was determined by NMR spectroscopy. As confirmed by XRD and DSC analysis, catalysts 1 and 3 produced amorphous terpolymer, whereas 2 yielded terpolymer with crystalline fragments of long ethylene sequences. When compared with poly‐(ethylene‐co‐norbornene), VNB increased both the glass transition temperatures and molar masses of terpolymers produced with the constrained geometry catalyst whereas decreased those for the metallocenes.