Copolymerization of propene and 1-hexene with isospecific and syndiospecific metallocene catalysts

SUMMARY SUMMARY Copolymerization of propene and 1-hexene has been carried out in toluene at 30°C in the presence of homogeneous methylaluminoxane (MAO)-activated 3 ansa-metallocenes, highly syndiospecific iPr(Cp)(Flu)ZrMe₂ ( 1 ), lower syndiospecific Et(Cp)(Flu)ZrMe₂ ( 2 ), and isospecific rac-(EBTHI)ZrMe₂ ( 3 ), in order to study the role of catalyst stereospecificity on comonomer incorporation. The incorporation of 1-hexene decreases in the following order: highly syndiospecific 1 /MAO catalyst > lower syndiospecific 2 /MAO catalyst > isospecific 3 /MAO catalyst. All copolymer chains contain the comonomer in nearly random distribution. The copolymers produced by 1 /MAO and 3 /MAO catalysts were composed of uniform chains, but that by 2 /MAO was fractionated into many fractions in the solvent extraction. Considerable rate enhancements were recorded in the copolymerization when the feed ratio of 1-hexene to propene is around 0.6 for all catalysts. Received: 16 December 1997/Revised version: 9 February 1998/Accepted: 19 February 1998     

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     

Poly(pent‐1‐ene) Synthesized with the Syndiospecific Catalyst i‐Pr(Cp)(9‐Flu)ZrCl2/MAO

1‐Pentene was polymerized with the syndiospecific catalyst system i‐PrC(Cp)(9‐fluorenyl)ZrCl₂/MAO. The molar mass of the resulting polymers depends strongly on the reaction temperature and decreases from M̄_w = 126 000 at 0°C to M̄_w = 46 000 at 100°C, but is more or less independent of the monomer and the MAO concentration. The influence of reaction temperature and concentrations of MAO and monomer on the type of end‐groups generated during the chain termination, as well as on the type of stereoerror, was investigated. The degree of tacticity was dependent on the polymerization temperature with [rrrr] > 0.99 at 0°C and [rrrr] = 0.75 at 100°C.     

Copolymerizations of ethylene with 1–decene over various ansa–metallocene complexes combined with Al( i-Bu) 3/ [CPh 3] [B(C 6F 5) 4] cocatalyst

Copolymerizations of ethylene with 1-decene were carried out with a series of stereospecific metallocene compounds, rac–(EBI)Zr(NMe₂)₂ [ 1, EBI = ethylene–1,2–bis( 1–indenyl)], rac–(EBI)Hf(NMe₂ (2), rac–Me₂Si( 1–C₅H₂–2–Me–4– ^t Bu)₂Zr(NMe₂)₂ (3), ethylidene(cyclopentadienyl)(9-fluorenyl)ZrMe2 [4, Et(Flu)(Cp)ZrMe2] and isopropylidene(cyclopentadienyl)(9–fluorenyl)ZrMe₂ [5, iPr(Flu)(Cp)ZrMe₂], combined with Al(i–Bu)₃/[CPh₃] [B(C₆F₅)₄] cocatalyst. All catalyst systems showed very high copolymerization rates and the 1–decene reactivity decreased in the order of 2 > 5 > 1 4 > 3. The reactivity product of ethylene and 1–decene (r _E x r _D) was below 1 except 3 catalyst, corresponding to random copolymer structures with an alternating character. The melting point (T_m), crystallinity (X_C), intrinsic viscosity ([] and density of the 1–decene/ethylene copolymers decreased markedly with an increase in the 1–decene content, regardless of the type of catalytic system.     

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     

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.     

Study on unsaturated structures of polyhexene,poly(4-methylpentene) and poly(3-methylpentene) prepared with metallocene catalysts

Hex-1-ene (hexene), 4-methylpent-1-ene (4-MP-1) and 3-methylpent-1-ene (3-MP-1), homopolymerizations were conducted by using metallocenes, En(Ind)₂ZrCl₂ and iPr(Cp)(Flu)ZrCl₂, with methylaluminoxane. ¹H NMR analyses of the resulting polymers were carried out to identify the unsaturated structures of these polymers. In polyhexene and poly(4-MP-1), the detected main unsaturated structure was di-substituted vinylene. On the other hand, in poly(3-MP-1), vinylidene and tri-substituted vinylene structures were mainly observed for the first time.     

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     

Incorporation of Core‐Twisted Perylene Bisimide Ligands into a Discrete Cp*Rh‐Based Molecular‐Rectangle via Coordination‐Driven Self‐Assembly

A tetranuclear metallarectangle ( 2 ) derived from dinuclear rhodium(III) building block [Cp*₂Rh₂(μ‐η²‐η²‐C₂O₄)]Cl₂ and imidazole‐based perylene bisimide ditopic ligand ( 1 ) ( 1= 2,9‐bis(4‐(1H‐imidazol‐1‐yl)phenyl)‐5,6,12,13‐tetrachloroanthra‐[2,1,9‐def:6,5,10‐d′e′f′]diisoquinoline‐1,3,8,10(2H,9H)‐tetraone) in presence of silver triflate is reported. The self‐assembled metallarectangle 2 is fully characterized by NMR, ESI‐MS, UV‐vis absorption, fluorescence emission spectroscopy and cyclic voltammetry. The X‐ray diffraction analysis reveals a twisted conformational geometry of metallarectangle 2 caused by essential steric demands of the two side‐by‐side chlorine atoms. In addition, the analyzed structure also elaborates the intermolecular electrostatic interactions between the electron‐deficient diimide moiety of 2 and the electron‐rich planar phenanthrene molecule.     

Umsetzungen des Pentamethylcyclopentadienyl‐Halbsandwichkomplexes Cp*Ta(CO)4 mit Chlor,Brom und Iod

The reaction of Cp*Ta(CO)₄ ( 1 ) (Cp* = η⁵‐pentamethylcyclopentadienyl, η⁵‐C₅Me₅) with chlorine leads to Cp*TaCl₄ ( 2a ), whereas the corresponding reactions with bromine or iodine give the oxo‐bridged complexes [Cp*TaX₃]₂(μ‐O) (X = Br ( 3b ), I ( 3c )). The oxygen atom apparently stems from a carbonyl ligand. In the presence of air, the binuclear complexes 3a , b are converted into mononuclear Cp*Ta(O)X₂ ( 4b , c ). The X‐ray structural determination of [Cp*TaBr₃]₂(μ‐O) ( 3b ) confirms a linear Ta–O–Ta bridge with a Ta–O distance of 190,4(1) pm.     

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.     

The detailed analysis of the vinylidene structure of metallocene-catalyzed polypropylene

The vinylidene structures in polypropylenes produced by ethylenebis(indenyl)zirconiumdichloride (En(Ind)₂ZrCl₂), 1, and isopropyl(cyclopentadienyl)(fluorenyl)zirconiumdichloride (iPr(Cp)(Flu)ZrCl₂), 2, were analyzed by ¹H NMR. The vinylidene group adjacent to the chain end was clearly distinguished from other internal vinylidene structures for the first time using 1,2-dichlorobenzene as solvent. The polypropylene produced by 2 had much internal vinylidene groups compared with one by 1.     

Syndiospecific polymerization of propene under different processes with different bridged [(RPh)2C(Cp)(2,7-BuFlu)]ZrCl2 metallocene catalysts

The synthesis of syndiotactic polypropene was achieved by using new C_S-symmetric ansa-metallocene catalysts of the type [Ph′₂C(Cp)(2,7-^tertBu₂Flu)]ZrCl₂ (Ph′₂=Ph₂, (4-MePh)₂, 3,4′-Me₂Ph₂, (4-OCH₃Ph)₂). Applying these catalysts, the influence of the substitution pattern of the bridge on the polymerization performance can be studied and highly syndiotactic polypropene (rrrr>99%) with high molar masses and high melting temperatures (up to 153 °C) was obtained.Propene was polymerized at different temperatures under four sets of conditions: in toluene solution, bulk, toluene slurry, and gas phase with NaCl as stirred bed material. Methylaluminoxane (MAO) and methylaluminoxane supported on silicagel (MAO/SiO₂) were used as cocatalyst, respectively. In order to estimate the influence of the process on the single site properties of the catalysts, comparisons were made between polymer properties, i.e. microstructure, melting temperature, molar mass, and polymer morphology, thus allowing the effect of the support on the catalyst to be observed.     

Study on chain end structures of polypropylenes prepared with different symmetrical metallocene catalysts

Propylene homopolymerizations were conducted by using three kinds of metallocenes: Cp₂ZrCl₂, En(Ind)₂ZrCl₂ and iPr(Cp)(Flu)ZrCl₂, all of which were activated with methylaluminoxane. Detailed NMR analyses of the chain ends in the resulting polymers were carried out to discuss the chain end structures of the polypropylenes and the mechanism of polymerization. The characteristic of each metallocene for the mechanism of polymerization was also described.     

Ethene/styrene-copolymerizations with [Me2C(3-RCp)(Flu)]ZrCl2/MAO (R=H,Me,tertBu,cHex, Ph)

Two new C₁-symmetric zirconocenes of the type [Me₂C(3-RCp)(Flu)]ZrCl₂ bearing a phenyl (Ph) or a cyclohexyl (cHex) substituent on the cyclopentadienyl ring were synthesized. Copolymerizations of ethene and styrene were carried out using these catalysts and compared to the results obtained with the methyl- and ^tertbutyl-substituted as well as with the unsubstituted system. By the introduction of the phenyl substituent both the activities and the molar masses could be increased whilst the styrene incorporation was comparable to that achieved with the unsubstituted system. In the case of the alkyl substituted systems (R=Me, ^tertBu, cHex) the styrene incorporation is decreased drastically and molar masses and activities are also strongly effected.     

Synthesis and properties of hybrid materials obtained by in situ copolymerization of ethylene and propylene in the presence of Al2O3 nanofibers (NafenTM) on catalytic system rac‐Et(2‐MeInd)2ZrMe2/isobutylalumoxane

Nanofibers of Al₂O₃ (commercial product Nafen^TM) with characteristic length of ～100 nm and diameter of ～10 nm were used to create new hybrid materials based on copolymer of ethylene and propylene. Nanocomposites were obtained by in situ catalytic copolymerization on the system rac‐Et(2‐MeInd)₂ZrMe₂/isobutylalumoxane. Formation of the nanocomposites with uniform distribution of Nafen nanoparticles in polymer matrix was confirmed by scanning and transmission electron microscopy. According to dynamic mechanical analysis data, introduction of the nanofiller in an amount of up to 3 wt % leads to an increase in glass transition temperature by 10 °C (E″) and by 21 °C (tan δ). The nanocomposites exhibit improved physico‐mechanical properties (tensile strength and elongation at break). It is shown that the nanofiller significantly improves resistance of the nanocomposite to the thermo‐oxidative and thermal degradation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44678.     

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     

Hydrogen-Atom Transfer Oxidation with H2O2 Catalyzed by [FeII(1,2-bis(2,2′-bipyridyl-6-yl)ethane(H2O)2]2+: Likely Involvement of a (μ-Hydroxo)(μ-1,2-peroxo)diiron(III) Intermediate

The iron(II) triflate complex ( 1 ) of 1,2-bis(2,2′-bipyridyl-6-yl)ethane, with two bipyridine moieties connected by an ethane bridge, was prepared. Addition of aqueous 30 % H₂O₂ to an acetonitrile solution of 1 yielded 2 , a green compound with λ_max=710 nm. Moessbauer measurements on 2 showed a doublet with an isomer shift (δ) of 0.35 mm/s and a quadrupole splitting (ΔE_Q) of 0.86 mm/s, indicative of an antiferromagnetically coupled diferric complex. Resonance Raman spectra showed peaks at 883, 556 and 451 cm⁻¹ that downshifted to 832, 540 and 441 cm⁻¹ when 1 was treated with H₂¹⁸O₂. All the spectroscopic data support the initial formation of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that oxidizes carbon-hydrogen bonds. At 0 °C 2 reacted with cyclohexene to yield allylic oxidation products but not epoxide. Weak benzylic C−H bonds of alkylarenes were also oxidized. A plot of the logarithms of the second order rate constants versus the bond dissociation energies of the cleaved C−H bond showed an excellent linear correlation. Along with the observation that oxidation of the probe substrate 2,2-dimethyl-1-phenylpropan-1-ol yielded the corresponding ketone but no benzaldehyde, and the kinetic isotope effect, k_H/k_D, of 2.8 found for the oxidation of xanthene, the results support the hypothesis for a metal-based H-atom abstraction mechanism. Complex 2 is a rare example of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that can elicit the oxidation of carbon-hydrogen bonds.     

Ruthenium‐Catalyzed O‐Allylation of Phenols from Allylic Chlorides via Cationic [Cp*(η3‐allyl)(MeCN)RuX][PF6] Complexes

The [Cp*(MeCN)₃Ru(II)][PF₆] complex is an efficient catalyst precursor for the O‐allylation of phenols with allylic chlorides in the presence of K₂CO₃ under mild conditions. This ruthenium precursor affords branched allyl aryl ethers according to a regioselective reaction, which contrasts with the uncatalyzed nucleophilic substitution from the same substrates. Stable (η³‐allyl)Ru(IV) cationic complexes resulting from the reaction of [Cp*(MeCN)₃Ru][PF₆] with allylic halides were identified as intermediate catalytic species. An X‐ray structure determination of the complex [Cp*(MeCHCHCH₂)(MeCN)RuBr][PF₆] disclosed an (endo‐trans‐MeCHCHCH₂) allylic ligand. The structural information obtained from the study of Cp*(allyl)Ru(IV) complexes indicated that electronic effects at the coordinated allylic ligand likely account for the better regioselectivity obtained from cinnamyl chloride as compared to aliphatic allylic chlorides.     

Crystallization kinetics of PE‐b‐isotactic PMMA diblock copolymer synthesized using SiMe2(Ind)2ZrMe2 and MAO cocatalyst

Polyethylene‐b‐poly(methyl methacrylate) (PE‐b‐PMMA) diblock copolymer has important interfacial applications. Hence, a PE‐b‐isotactic PMMA diblock copolymer was synthesized using SiMe₂(Ind)₂ZrMe₂ and MAO cocatalyst. The polymerization mechanism and the origin of PMMA isotacticity were duly explained. An appropriate nonisothermal Avrami‐Erofeev crystallization model was developed to compare the crystallization kinetics of the above copolymer with that of a PE homopolymer. For both polymers, the model well matched the entire differential scanning calorimeter crystallinity profile, notably for a single Avrami‐Erofeev index, and predicted cylindrical crystal growth. This model particularly overcomes the limitations of the published nonisothermal crystallization models, and provides interesting insight into PE crystallization. The PMMA block significantly decreased the heats of crystallization and fusion, % crystallinity, and the relative crystallization function; increased the nonisothermal crystallization rate constant; and introduced minimal dilution effect whereas the PE block formed a continuous or percolated phase. This study correlates catalyst structure, copolymer block tacticity, and PE nonisothermal crystallization and melting behavior. © 2012 American Institute of Chemical Engineers AIChE J, 59: 200–214, 2013