Branched polyethylene prepared by in situ copolymerization of ethylene with monotitanocene and modified methylaluminoxane catalyst

Branched polyethylene was synthesized in heptane used as a polymerization medium with monotitanocene catalyst composed of η⁵‐pentamethylcyclopentadienyl tribenzyloxy titanium and modified methylaluminoxane (mMAO) that contained different amounts of residual trimethylaluminum (TMA). The residual TMA more strongly reduced Ti(IV) complexes to Ti(III) and Ti(II) ones, and Ti(IV) active species were suggested to be more effective for ethylene polymerization. Influences of the polymerization temperature and Al/Ti molar ratio on the catalytic activity and the degree of branching, branch length, and molecular weight of polyethylene were investigated. The obtained polymers were confirmed by ¹³C NMR to be higher molecular weight polyethylene containing significant amounts of isolated ethyl branches, butyl branches, or both. Branched polyethylene was prepared by the in situ copolymerization of ethylene with 1‐butene and 1‐hexene, which were formed through a proposed mechanism including metallcycloheptane and metallcyclopentane intermediates of Ti(II) species that were produced by the reaction of Ti(IV) complexes with TMA coexisting in mMAO. There was a remarkable increase in the chance of 1‐butene being produced from metallcyclopentane of Ti(II) intermediates with an increase in the polymerization temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4258–4263, 2000     

Effect of cocatalyst on the chain microstructure of polyethylene made with CGC‐Ti/MAO/B(C6F5)3

This investigation studied the solution polymerization of ethylene in Isopar E in a semibatch reactor using CGC‐Ti as catalyst and methylalumoxane (MAO) and tris(pentaflourophenyl)borane [B(C₆F₅)₃] as cocatalysts. The effects of cocatalyst type and amount on the chain microstructure were investigated. ¹³C NMR and gel permeation chromatography were used to determine the long‐chain branching (LCB) content and molecular weight distribution (MWD), respectively, of the samples. It was observed that higher concentrations of MAO increased the LCB content and decreased the molecular weight of the polymer. On the other hand, increasing the amount of B(C₆F₅)₃ lowered the LCB content, increased the molecular weight, and broadened MWD significantly. We believe that this approach can be used as an efficient way to control the microstructure of polyolefins made with these catalytic systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3055–3061, 2004     

Long‐chain‐branched polyethene by the copolymerization of ethene and nonconjugated α,ω‐dienes

Ethene was copolymerized (1) with 1,5‐hexadiene with rac‐ethylenebis(indenyl)zirconium dichloride/methylaluminoxane (MAO) used as a catalyst and (2) with 1,7‐octadiene with bis(n‐butylcyclopentadienyl)zirconium dichloride/MAO and rac‐ethylenebis(indenyl)hafnium dichloride (Et[Ind]₂HfCl₂)/MAO used as catalysts at 80 °C in toluene. The copolymer microstructure and the influence of diene incorporation on the rheological properties were examined. Ethene and 1,5‐hexadiene formed a copolymer in which a major fraction of the 1,5‐hexadiene was incorporated into rings and a small fraction formed 1‐butenyl branches. The copolymerization of ethene with 1,7‐octadiene resulted in a higher selectivity toward branch formation. Some of the branches formed long‐chain‐branching (LCB) structures. The ring formation selectivity increased with decreasing ethene concentration in the polymerization reactor. Melt rheological properties of the diene copolymers resembled those of metallocene‐catalyzed LCB homopolyethenes and depended on the vinyl content, the catalyst, and the polymerization conditions. At high diene contents, all three catalysts produced crosslinked polyethene. This was especially pronounced with Et[Ind]₂HfCl₂, where only 0.2 mol % 1,7‐octadiene in the copolymer was required to achieve significantly modified rheological properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3805–3817, 2001     

Synthesis and Characterization of Long‐Chain‐Branched Polyolefins with Metallocene Catalysts: Copolymerization of Ethylene with Poly(ethylene‐co‐propylene) Macromonomer

Poly(ethylene‐co‐propylene) macromonomer (EPM) was synthesized in a high‐temperature continuous stirred tank reactor (CSTR) with [C₅Me₄(SiMe₂N^tBu)]TiMe₂ (CGC‐Ti) as the catalyst system. PE samples with EPM long chain branching (LCB) were produced by semi‐batch copolymerization of ethylene and EPM with CGC‐Ti. The LCB frequencies were up to 21.8 EPM side chains per PE backbone. The effects of temperature and ethylene pressure on the degree of EPM grafting and catalyst activity were examined.

Incorporation of EPM into a growing PE chain forming an LCB polymer.     

Some mixed cyclopentadienyl–indenyl zirconium complexes with PhCH2 or PhCH2CH2 substituents in ethylene polymerization

(RCp)(R′Ind)ZrCl₂ complexes 1 – 6 (Cp = cyclopentadienyl; Ind = indenyl; 1 , R = PhCH₂ and R′ = H; 2 , R = PhCH₂ and R′ = PhCH₂; 3 , R = PhCH₂CH₂ and R′ = H; 4 , R = PhCH₂CH₂ and R′ = PhCH₂; 5 , R = o‐Me? PhCH₂CH₂ and R′ = H; 6 , R = o‐Me? PhCH₂ and R′ = H) were synthesized and characterized with ¹H NMR, elemental analysis, mass spectrometry, and infrared spectroscopy. Their catalytic behaviors were compared with those of (Et₃SiCp)(PhCH₂CH₂Cp)ZrCl₂, (PhCH₂Cp)₂ZrCl₂, (PhCH₂‐ CH₂Cp)₂ZrCl₂, (o‐Me? PhCH₂CH₂Cp)₂ZrCl₂, and (Ind)₂ZrCl₂ in ethylene polymerization in the presence of methylaluminoxane. Complex 5 showed high activity up to 2.43 × 10⁶ g of polyethylene (PE)/mol of Zr h, and complex 4 produced PE with bimodal molecular weight distributions. The methyl group at the 2‐position of phenyl in complex 5 increased the activity greatly. The relationships between the polymerization results and the structures were analyzed with NMR spectral data. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1261–1269, 2005     

Preparation of linear low‐density polyethylene by the in situ copolymerization of ethylene with an iron oligomerization catalyst and rac‐ethylene bis(indenyl) zirconium (IV) dichloride

An iron oligomerization catalyst, [(2‐ArN?C(Me))₂C₅H₃N]FeCl₂ [Ar = 2,6‐C₆H₃(F)₂], was combined with rac‐ethylene bis(indenyl)zirconium (IV) dichloride [rac‐Et(Ind)₂ZrCl₂] to prepare linear low‐density polyethylene (LLDPE) by the in situ copolymerization of ethylene. A series of LLDPEs with different properties were prepared by the alteration of the reaction temperature, Fe/Zr molar ratio, Al/(Fe + Zr) molar ratio, and reaction time. The structures of the polymers were characterized with differential scanning calorimetry, ¹³C NMR, gel permeation chromatography (GPC), and so forth. The melting points, crystallizations, and densities of the resulting products increased, and the average branching degree decreased, as the reaction temperature, Al/(Fe + Zr) ratio, and reaction time increased. The melting points, crystallizations, and densities of the polymers decreased, and the average branching degree increased, when the Fe/Zr ratio increased. The ¹³C NMR and GPC results showed that there were no unreacted α‐olefins remaining in the resulting polymers because the percentage of low‐molar‐mass sections (C₄–C₁₀) of the oligomers obtained with this catalyst was very high (>70%). In addition, the formation of polymers with two melting points under different reaction conditions was examined in detail, and the results indicated that the two melting points of the polymers could be attributed to polyethylene with different branches. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 984–993, 2005     

Comparing Long‐Chain Branching Mechanisms for Ethylene Polymerization with Metallocenes and Other Single‐Site Catalysts: What Simulated Microstructures Can Teach Us

Three different long‐chain branch (LCB) formation mechanisms for ethylene polymerization with metallocenes in solution polymerization semi‐batch and continuous stirred‐tank reactors are modeled to predict the microstructure of the resulting polymer. The three mechanisms are terminal branching, C–H bond activation, and intramolecular random incorporation. Selected polymerization parameters are varied to observe how each mechanism affects polymer microstructure. Increasing the ethylene concentration during semi‐batch polymerization reduces the LCB frequency of polymers made with the terminal branching and intramolecular mechanisms, but has no effect on those made with the C–H bond activation mechanism, which disagrees with most previous data published in the literature. The intramolecular mechanism predicts that LCB frequencies hardly depend on polymerization time or ethylene conversion, which also disagrees with the published experimental data for these systems. For continuous polymerization reactors, experimental data relating polydispersity to LCB frequency can be well described with the terminal branching mechanism, but both C–H bond activation and intramolecular models fail to describe this experimental relationship. Therefore, detailed simulations confirm that the terminal branching mechanism is indeed the most likely mechanism for LCB formation when ethylene is polymerized with single‐site coordination catalysts such as metallocenes in solution polymerization reactors.     

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene,propylene homopolymerizations,and their copolymerization

A series of ethylene, propylene homopolymerizations, and ethylene/propylene copolymerization catalyzed with rac‐Et(Ind)₂ZrCl₂/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2‐thiophenecarbonyl chloride to label a 2‐thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C^*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene homopolymerization) and copolymer composition with time were also studied. [C^*]/[Zr] strongly depended on type of monomer, with the propylene homopolymerization system presented much lower [C^*]/[Zr] (ca. 25%) than the ethylene homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C^*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C^*]/[Zr] of ethylene homopolymerization (ca. 70%). The chain propagation rate constant (k_p) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 867–875     

Ethylene (Co)Polymerization with Metallocene Catalysts Encapsulated in Gel‐Type Poly(styrene‐co‐divinylbenzene) Beads

Gel‐type poly(styrene‐co‐divinylbenzene) beads (PS bead) were used as a carrier to encapsulate metallocene catalysts through a simple swelling‐shrinking procedure. The catalytic species were homogeneously distributed in the PS bead particle. The catalyst exhibited high and stable ethylene polymerization and ethylene/1‐hexene copolymerization activity affording uniform spherical polymer particles (1 mm). Polymerization rate profiles exhibited slow initiation and stable increase in polymerization activity with time.     

Direct synthesis of linear low‐density polyethylene of ethylene/1‐hexene from ethylene with a tandem catalytic system in a single reactor

Tandem catalysis offers a promising synthetic route to the production of linear low‐density polyethylene. This article reports the use of homogeneous tandem catalytic systems for the synthesis of ethylene/1‐hexene copolymers from ethylene stock as the sole monomer. The reported catalytic systems employ the tandem action between an ethylene trimerization catalyst, (η⁵‐C₅H₄CMe₂C₆H₅)TiCl₃ ( 1 )/modified methylaluminoxane (MMAO), and a copolymerization metallocene catalyst, [(η⁵‐C₅Me₄)SiMe₂(^tBuN)]TiCl₂ ( 2 )/MMAO or rac‐Me₂Si(2‐MeBenz[e]Ind)₂ZrCl₂ ( 3 )/MMAO. During the reaction, 1 /MMAO in situ generates 1‐hexene with high activity and high selectivity, and simultaneously 2 /MMAO or 3 /MMAO copolymerizes ethylene with the produced 1‐hexene to generate butyl‐branched polyethylene. We have demonstrated that, by the simple manipulation of the catalyst molar ratio and polymerization conditions, a series of branched polyethylenes with melting temperatures of 60–128 °C, crystallinities of 5.4–53%, and hexene percentages of 0.3–14.2 can be efficiently produced. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4327–4336, 2004     

Production of Long‐Chain Branched Polyolefins with Two Single‐Site Catalysts: Comparing CSTR and Semi‐Batch Performance

We developed a mathematical model to describe the solution polymerization of olefins with two single‐site catalysts in a series of two CSTRs. The model was used to simulate processes where semi‐crystalline macromonomers produced in the first reactor are incorporated as long chain branches onto amorphous (or lower crystallinity) chains in the second reactor (cross‐products). The simulation results show that CSTRs are more efficient to make chains with high LCB density and high weight percent of cross‐products. The model can also predict the polydispersity index, average chain lengths, and fractions of the different polymer populations, and help the polymer reactor engineer formulate new products with complex microstructures.

     

Bis(salicylaldiminate)copper(II)/methylaluminoxane catalysts for homo‐ and copolymerizations of ethylene and methyl methacrylate

Bis(salicylaldiminate)copper(II) complexes, when activated with methylaluminoxane, catalyzed the homo‐ and copolymerizations of ethylene and methyl methacrylate (MMA). The activity in the MMA homopolymerization was influenced by the electronic and steric characteristics of the Cu(II) precursors as well as the cocatalyst concentration. The same systems revealed modest activity also in the homopolymerization of ethylene, giving a highly linear polyethylene, and in its copolymerization with MMA. These copolymers exhibited a very high content of polar groups (MMA units > 70 mol %) and were characterized by a high molecular weight and polydispersity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1134–1142, 2007     

Styrene‐ethylene co‐oligomerization with bis‐(diphenylphosphino)‐amine/chromium catalysts and the use of the co‐oligomerization products in copolymerization reactions with metallocenes

Ethylene‐styrene (or 4‐methylstyrene) co‐oligomerization using various bis(diphenylphoshino)amine ligands in combination with chromium is discussed. GC analysis of the reaction mixture shows that various phenyl‐hexene and phenyl‐octene isomers are formed either through cotrimerization or cotetramerization. It seems that the more bulky ligands display lower selectivity to co‐oligomerization and favor ethylene homo‐oligomerization. Subsequent copolymerization of the oligomerization reaction mixture using a metallocene polymerization catalyst results in a copolymer with a branched structure as indicated by Crystaf and ¹³C NMR analysis. Assignments of the ¹³C NMR spectrum are proposed from an APT NMR experiment combined with calculated NMR chemical shift data using additivity rules. An indication of the ability of the different co‐oligomerization products to copolymerize into the polyethylene chain could be established from these assignments. Unreacted styrene and the more bulky isomers, 3‐phenyl‐1‐hexene and 3‐phenyl‐1‐octene, are not readily incorporated while branches resulting from the other isomers present in the co‐oligomerization reaction mixture are detected in the NMR spectrum. © 2008 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 46: 1488–1501, 2008     

Effect of substituents on the catalytic properties of bis(cyclopentadienyl)zirconium dichloride complexes with polymethylaluminoxane and AlBu1 3/CPh3B(C6F5)4 cocatalysts in ethylene polymerization

The catalytic properties of the complexes (RCp)₂ZrCl₂ (R=H, Me, Prⁱ, Buⁿ, Buⁱ, Me₃Si,cyclo-C₆H₁₁), and Me₂SiCp^*NBuⁱZrCl₂ (Cp^*=C₅(CH₃)₄) combined with the AlBuⁱ ₃−CPh₃B(C₆F₅)₄ cocatalyst in ethylene polymerization were studied. The specific activity of the substituted bis-cyclopentadienyl complexes decreases in the sequence: Me>Prⁱ>Buⁿ>Buⁱ>Me₃Si>cyclo-C₆H₁₁, which corresponds to the activity sequence for these complexes activated by polymethylaluminoxane (MAO) but is 4–20 times lower in absolute value. Comparison of the polyethylene samples obtained in the presence of the same complexes with MAO and AlBuⁱ ₃−CPh₃B(C₆F₅)₄ cocatalysts showed that polyethylene with much higher molecular mass, melting point, and crystallinity is formed in the presence of the ternary catalytic systems, and this indicates a different nature of the active sites of the catalytic systems. The effective activation energy of polymerization (≈3.6 kcal mol⁻¹), first order with respect to monomer and ≈0.4 order with respect to organoaluminum component, was found for the (PrⁱCo)₂ZrCl₂−AlBuⁱ ₃−CPh₃B(C₆F₅)₄ catalytic system. It was proposed on the basis of the kinetic data that AlⁱBu₃ enters into the composition of the active site to form a bridged heteronuclear cationic complex. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp 301–307, February, 2000.     

Synthesis of well‐defined multigraft copolymers by a two‐step living radical polymerization with nitroxyl‐functionalized poly(methyl methacrylate)

Novel multigraft copolymers of poly(methyl methacrylate‐graft‐polystyrene) (PMMA‐g‐PS) in which the number of graft PS side chains was varied were prepared by a subsequent two‐step living radical copolymerization approach. A polymerizable 4‐vinylbezenyl 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) monomer (STEMPO), which functioned as both a monomer and a radical trapper, was placed in a low‐temperature atom transfer radical polymerization (60°C) process of methyl methacrylate with ethyl 2‐bromopronionate (EPNBr) as an initiator to gain ethyl pronionate‐capped prepolymers with TEMPO moieties, PMMA‐STEMPOs. The number of TEMPO moieties grafted on the PMMA backbone could be designed by varying STEMPO/EPNBr, for example, the ratios of 1/2, 2/3, or 3/4 gained one, two, or three graft TEMPO moieties, respectively. The resulting prepolymers either as a macromolecular initiator or a trapper copolymerized with styrene in the control of stable free‐radical polymerization at an elevated temperature (120 °C), producing the corresponding multigraft copolymers, PMMA‐g‐PSs. The nitroxyl‐functionalized PMMA prepolymers produced a relatively high initiation efficiency (>0.8) as a result of the stereohindrance and slow diffusion of TEMPO moieties connected on the long PMMA backbone. The polymerization kinetics in two processes showed a living radical polymerization characteristic. The molecular structures of these prepolymers and graft copolymers were well characterized by combining Fourier transform infrared spectroscopy, gel permeation chromatography, chemical element analysis, and ¹H NMR. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1876–1884, 2002     

Simulation of Polymerization and Long Chain Branch Formation in a Semi‐Batch Reactor Using Two Single‐Site Catalysts

We developed a mathematical model for the solution polymerization of olefins in a semi‐batch reactor with two single‐site catalysts. In the propylene polymerization case, our objective is to study the production of a thermoplastic elastomer using two catalysts, one capable of forming isotactic chains containing terminal vinyl bonds (macromonomers) and the other producing atactic chains while also being able to copolymerize macromonomers to form long chain branches. A similar thermoplastic elastomer can be produced by polymerizing ethylene and α‐olefin comonomers when the α‐olefin reactivity ratios of the two catalysts are significantly different.

     

Ethylene/1‐octene copolymerization studies with in situ supported metallocene catalysts: Effect of polymerization parameters on the catalyst activity and polymer microstructure

Ethylene and 1‐octene copolymerizations were carried out with an in situ supported rac‐[dimethylsilylbis(methylbenzoindenyl)] zirconium dichloride catalyst. In a previous study, it was found that some in situ supported metallocenes produced polyethylene/α‐olefin copolymers with broad and bimodal short chain branching distributions and narrow molecular weight distributions. The ability to produce polyolefins with multimodal microstructural distributions in a single metallocene and a single reactor is attractive for producing polymers with balanced properties with simpler reactor technology. In this study, a factorial experimental design was carried out to examine the effects of the polymerization temperature and ethylene pressure, the presence of hydrogen and an alkylaluminum activator, and the level of the comonomer in the feed on the catalyst activity, short chain branching distribution, and molecular weight distribution of the polymer. The temperature had the most remarkable effect on the polymer microstructure. At high 1‐octene levels, the short chain branching distribution of the copolymer broadened significantly with decreasing temperature. Several factor interactions, including the hydrogen and alkylaluminum concentrations, were also observed, demonstrating the sensitivity of the catalyst to the polymerization conditions. For this catalyst system, the responses to the polymerization conditions are not easily predicted from typical polymerization mechanisms, and several two‐factor interactions seem to play an important role. Given the multiple‐site nature of the catalyst, it has been shown that predicting the polymerization activity and the resulting microstructure of the polymer is a challenging task. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4426–4451, 2002     

Size‐exclusion chromatography coupled to multiangle light scattering detection of long‐chain branching in polyethylene made with phillips catalyst

Size‐exclusion chromatography coupled to multiangle light scattering (SEC‐MALS) has been used to detect long‐chain branching (LCB) in polyethylene (PE) from Cr/silica catalysts for the first time. The observed LCB response to several catalyst and reactor variables mostly confirms earlier conclusions drawn from rheological measurements. However, SEC‐MALS has also shed additional light on a few previously unanswered questions. Above all, SEC‐MALS shows the placement of branching within the MW distribution, which was not previously known, and which may explain some of the unique molding behavior of Cr‐derived PE. This new SEC‐MALS data also provide insight into the mechanism of LCB formation, which is discussed. Like earlier studies based on rheology, this new study demonstrates that the commonly accepted view of macromer incorporation may be overly simplistic. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

FTIR, 13C NMR,and GPC analysis of high‐propylene content co‐ and terpolymers with ethylene and higher α‐olefins synthesized with EtInd2ZrCl2/MAO

This article reports the results of propylene/α‐olefin copolymerization and propylene/ethylene/α‐olefin terpolymerization using low concentrations (less than 5 mol %) of long α‐olefins such as 1‐octene, 1‐decene, and 1‐dodecene. Kinetics data are presented and discussed. The highest activity was found with the longest α‐olefin studied (1‐dodecene). A possible explanation is proposed for this and other characteristics of the polymers obtained. The effect of low‐ethylene contents (4 mol % in the gas phase) on the copolymerization of propylene/α‐olefins was also examined. The polymers synthesized were characterized by ¹³C NMR, gel permeation chromatography, DSC, Fourier transform infrared spectroscopy, and wide‐angle X‐ray scattering. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2005–2018, 2001