Hydrogen effects in propylene polymerization reactions with titanium‐based Ziegler–Natta catalysts. I. Chemical mechanism of catalyst activation

The hydrogen activation effect in propylene polymerization reactions with Ti‐based Ziegler–Natta catalysts is usually explained by hydrogenolysis of dormant active centers formed after secondary insertion of a propylene molecule into the growing polymer chain. This article proposes a different mechanism for the hydrogen activation effect due to hydrogenolysis of the Ti? iso‐C₃H₇ group. This group can be formed in two reactions: (1) after secondary propylene insertion into the Ti? H bond (which is generated after β‐hydrogen elimination in the growing polymer chain or after chain transfer with hydrogen), and (2) in the chain transfer with propylene if a propylene molecule is coordinated to the Ti atom in the secondary orientation. The Ti? CH(CH₃)₂ species is relatively stable, possibly because of the β‐agostic interaction between the H atom of one of its CH₃ groups and the Ti atom. The validity of this mechanism was demonstrated in a gas chromatography study of oligomers formed in ethylene/α‐olefin copolymerization reactions with δ‐TiCl₃/AlEt₃ and TiCl₄/dibutyl phthalate/MgCl₂–AlEt₃ catalysts. A quantitative analysis of gas chromatography data for ethylene/propylene co‐oligomers showed that the probability of secondary propylene insertion into the Ti? H bond was only 3–4 times lower than the probability of primary insertion. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1353–1365, 2002     

Active center determinations on MgCl2‐supported fourth‐ and fifth‐generation Ziegler–Natta catalysts for propylene polymerization

Active center determinations on different Ziegler–Natta polypropylene catalysts, comprising MgCl₂, TiCl₄, and either a diether or a phthalate ester as internal donor, have been carried out by quenching propylene polymerization with tritiated ethanol, followed by radiochemical analysis of the resulting polymers. The purpose of this study was to determine the factors contributing to the high activities of the catalyst system MgCl₂/TiCl₄/diether—AlEt₃. Active center contents (C*) in the range 2–8% (of total Ti present) were measured and a strong correlation between catalyst activity and active center content was found, indicating that the high activity of the diether‐containing catalysts is due to an increased proportion of active centers rather than to a difference in propagation rate coefficients. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1635–1647, 2006     

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     

Hydrogen effects in propylene polymerization reactions with titanium‐based Ziegler–Natta catalysts. II. Mechanism of the chain‐transfer reaction

Hydrogen is a very effective chain‐transfer agent in propylene polymerization reactions with Ti‐based Ziegler–Natta catalysts. However, measurements of the hydrogen concentration effect on the molecular weight of polypropylene prepared with a supported TiCl₄/dibutyl phthalate/MgCl₂ catalyst show a peculiar effect: hydrogen efficiency in the chain transfer significantly decreases with concentration, and at very high concentrations, hydrogen no longer affects the molecular weight of polypropylene. A detailed analysis of kinetic features of chain‐transfer reactions for different types of active centers in the catalyst suggests that chain transfer with hydrogen is not merely the hydrogenolysis reaction of the Ti? C bond in an active center but proceeds with the participation of a coordinated propylene molecule. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1899–1911, 2002     

Co‐ and terpolymerization of ethylene,propylene, and higher α‐olefins with high propylene contents using metallocene catalysts

The copolymerization of propylene/ethylene and terpolymerization of propylene/ethylene/α‐olefins using long‐chain α‐olefins such as 1‐octene and 1‐decene have been carried out using EtInd₂ZrCl₂//methylaluminoxane. High concentrations of propylene and low concentrations of α‐olefins (near 2 mol % of the total olefin concentration in the liquid phase) were used. The effect of the ethylene concentration in copolymerizations of propylene/α‐olefins was studied at medium ethylene contents (12 and 40 mol % in the gas phase). The polymers were molecularly characterized by gel permeation chromatography‐multiangle laser light scattering, wide‐angle X‐ray scattering, Fourier transform infrared spectroscopy, and DSC analyses. The shorter α‐olefin studied (1‐octene) produced the highest improvement of activity in terpolymerization at 12 mol % ethylene in the gas phase. About 2 mol % of 1‐octene in the liquid phase increases the activity and decreases the molecular weight of terpolymers with respect to corresponding copolymers, whereas the mp is increased by almost 30 °C. The “termonomer effect” is less evident when higher amounts of ethylene are used. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1136–1148, 2001     

Synthesis of polypropylene graft copolymers by the combination of a polypropylene copolymer containing pendant vinylbenzene groups and atom transfer radical polymerization

This article discusses a facile and inexpensive reaction process for preparing polypropylene‐based graft copolymers containing an isotactic polypropylene (i‐PP) main chain and several functional polymer side chains. The chemistry involves an i‐PP polymer precursor containing several pendant vinylbenzene groups, which is prepared through the Ziegler–Natta copolymerization of propylene and 1,4‐divinylbenzene mediated by an isospecific MgCl₂‐supported TiCl₄ catalyst. The selective monoenchainment of 1,4‐divinylbenzene comonomers results in pendant vinylbenzene groups quantitatively transformed into benzyl halides by hydrochlorination. In the presence of CuCl/pentamethyldiethylenetriamine, the in situ formed, multifunctional, polymeric atom transfer radical polymerization initiators carry out graft‐from polymerization through controlled radical polymerization. Some i‐PP‐based graft copolymers, including poly(propylene‐g‐methyl methacrylate) and poly(propylene‐g‐styrene), have been prepared with controlled compositions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 429–437, 2005     

Kinetics of ethylene polymerization reactions with chromium oxide catalysts

Principal kinetic data are presented for ethylene homopolymerization and ethylene/1‐hexene copolymerization reactions with two types of chromium oxide catalyst. The reaction rate of the homopolymerization reaction is first order with respect to ethylene concentration (both for gas‐phase and slurry reactions); its effective activation energy is 10.2 kcal/mol (42.8 kJ/mol). The r₁ value for ethylene/1‐hexene copolymerization reactions with the catalysts is ～30, which places these catalysts in terms of efficiency of α‐olefin copolymerization with ethylene between metallocene catalysts (r₁ ～ 20) and Ti‐based Ziegler‐Natta catalysts (r₁ in the 80–120 range). GPC, DSC, and Crystaf data for ethylene/1‐hexene copolymers of different compositions produced with the catalysts show that the reaction products have broad molecular weight and compositional distributions. A combination of kinetic data and structural data for the copolymers provided detailed information about the frequency of chain transfer reactions for several types of active centers present in the catalysts, their copolymerization efficiency, and stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5315–5329, 2008     

Peculiarities of Ethylene Polymerization Reactions with Heterogeneous Ziegler–Natta Catalysts: Kinetic Analysis

The previously developed kinetic scheme for olefin polymerization reactions with heterogeneous Ziegler–Natta catalysts states that the catalysts have several types of active centers which have different activities, different stabilities, produce different types of polymer materials, and respond differently to reaction conditions. In the case of ethylene polymerization reactions, each type of center exhibits an unusual chemical feature: a growing polymer chain containing one ethylene unit, Ti—C₂H₅, is unusually stable and can decompose with the formation of the Ti—H bond. This paper examines quantitative kinetic ramifications of this chemical mechanism. Modeling of the complex kinetics scheme described in the Scheme demonstrates that it correctly and quantitatively predicts three most significant peculiarities of ethylene polymerization reactions, the high reaction order with respect to the ethylene concentration, reversible poisoning with hydrogen, and activation in the presence of α‐olefins.     

Copolymerization of propylene and disubstituted diallylsilanes involving intramolecular cyclization with stereoselective zirconocene catalysts

The copolymerization of propylene and disubstituted diallylsilanes [(CH₂ ?CH? CH₂? )₂R₂Si (R = CH₃ or C₆H₅)] was investigated with isoselective and syndioselective zirconocene catalysts with methylaluminoxane as a cocatalyst. The syndioselective catalyst showed a higher reactivity for disubstituted diallylsilanes than the isoselective catalysts. Diallyldimethylsilane was incorporated into the polymer chain via cyclization insertion preferentially and formed 3,5‐disubstituted dimethylsilacyclohexane units in the polypropylene main chain. In the copolymerization with diallyldiphenylsilane, diallyldiphenylsilane was copolymerized via both cyclization insertion and 1,2‐insertion, which formed a pendant allyl group. The structures of isolated silacyclohexane units, determined by ¹³C NMR and distortionless enhancement by polarization transfer spectroscopy, proved that the 1,2‐insertion of diallylsilanes proceeded with enantiomorphic site control; however, the diastereoselectivity of the cyclization reaction was independent of the stereoselectivity of the catalysts used, and cis‐silacyclohexane units were mainly formed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6083–6093, 2006     

Polymerization of alkenes with a post‐metallocene catalyst containing a titanium complex with an oxyquinolinyl ligand

Polymerization reactions of ethylene, propylene, higher 1‐alkenes (1‐hexene, 1‐octene, 1‐decene, vinyl cyclohexane, 3‐methyl‐1‐butene), and copolymerization reactions of ethylene with 1‐octene with a post‐metallocene catalyst containing an oxyquinolinyl complex of Ti and a combination of Al(C₂H₅)₂Cl and Mg(C₄H₉)₂ as a cocatalyst were studied. The catalyst is highly active and, judging by the broad molecular weight distribution of the polymers, contains several active center populations. The active centers differ not only in their kinetic parameters but also in stereospecificity. Most of the active centers produce essentially atactic polypropylene but a small fraction of the centers produces polypropylene of moderate isotacticity degree. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1844–1854     

Titanium complexes bearing carbamato ligands as catalytic precursors for propylene polymerization reactions

This report describes propylene polymerization reactions with titanium complexes bearing carbamato ligands, Ti(O₂CNMe₂)Cl₂ ( I ) and Ti(O₂CR₂)₄ [R₂ = NMe₂ ( II ), NEt₂ ( III ) and ( IV )]. Combinations of these complexes and MAO form catalysts for the synthesis of atactic polypropylene, as confirmed by FT‐IR, DSC and ¹³C NMR analysis. Effects of main reaction parameters on the catalyst activity were studied including the type of complex, solvent, temperature, and the [Al]/[Ti] molar ratio. The highest activity was observed when chlorobenzene was used as a solvent and AlMe₃‐depleted MAO was employed as a cocatalyst. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4095–4102     

A new route to atactic polypropylene: The second life of premetallocene homogeneous polymerization catalyst

Amorphous atactic polypropylene (PP) with an average molecular weight of 50,000–100,000 is produced by polymerizing propylene with a ternary Ti(Oiso‐Pr)₄ ‐ AlEt₂Cl/MgBu₂ catalyst at 30–50 °С. Main advantages of this catalyst compared with other catalysts capable of nearly exclusively producing atactic PP (such as some heterogeneous Ziegler‐Natta, metallocene and postmetallocene catalysts) are high activity, low cost and the ease of use: the catalyst is prepared in situ from three commercially available compounds readily soluble in aliphatic and aromatic hydrocarbons. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2124–2131     

Copolymerization of 3‐buten‐1‐ol and propylene with an isospecific zirconocene/methylaluminoxane catalyst

The copolymerization of propylene and 3‐buten‐1‐ol protected with alkylaluminum [trimethylaluminum (TMA) or triisobutylaluminum] was conducted with an isospecific zirconocene catalyst [rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride], combined with methylaluminoxane as a cocatalyst, in the presence of additional TMA or H₂ as the chain‐transfer reagent if necessary. The results indicated that end‐hydroxylated polypropylene was obtained in the presence of the chain‐transfer reagents because of the formation of dormant species after the insertion of the 3‐buten‐1‐ol‐based monomer followed by chain‐transfer reactions. The selectivity of the chain‐transfer reactions was influenced by the alkylaluminum protecting the comonomer and the catalyst structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5600–5607, 2004     

Manganese‐based transition metal complexes as new catalysts for olefin polymerizations

Three manganese complexes, Mn(acac)₃ (acac = acetylacetonate), Cp₂Mn (Cp = cyclopentadienyl), and Mn(salen)Cl [salen = 1,2‐cyclohexanediamino‐N,N′‐bis(3,5‐dit‐butyl‐salicylidene)], were used for ethylene and propylene polymerizations. These complexes, in combination with an alkylaluminum cocatalyst such as methylaluminoxane (MAO) or diethyl aluminum chloride (AlEt₂Cl), could promote ethylene polymerizations that yielded extremely high molecular weight linear polymers, but were inactive for propylene polymerizations. The counterparts supported on MgCl₂ showed activities even for propylene polymerizations and had remarkably enhanced activities for ethylene polymerizations. In the presence of an electron donor such as ethylbenzoate, the MgCl₂‐supported manganese‐based catalysts yielded a highly isotactic polypropylene with a high molecular weight. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3733–3738, 2001     

Increased rubber content in high impact polypropylene via a sirius ziegler‐natta catalyst containing nanoparticles

High impact polypropylene was produced in a two‐reactor polymerization process operating in series using two different Ziegler‐Natta catalysts (referred to as catalysts A and B) that had been prepared by Sirius emulsion technology in the absence and presence of SiO₂ nanoparticles, respectively. The homo polypropylene matrix was produced in liquid bulk and the ethylene/propylene rubber in gas phase under industrial conditions. Catalyst B was prepared with the same emulsion technology as catalyst A, except that SiO₂ nanoparticles (average particles size 80 nm) were added during catalyst preparation. Scanning electron microscopy studies showed that the nanoparticles were fairly evenly distributed within catalyst B particles, although there was some agglomeration. It was shown that the nanoparticles in catalyst B increased the internal porosity in the homo polypropylene matrix particles and this enabled a significant increase in the rubber content. Maximum rubber content, before running into stickiness problems, was approximately 25 wt % for catalyst A without nanoparticles, whereas the maximum rubber content for catalyst B was almost doubled to 45 wt % due to the beneficial transformation of the internal catalyst morphology by the nanoparticles. In addition, it was also found that the reaction was not mass transfer limited during the ethylene/propylene rubber polymerization stage, even at very high rubber contents where all pores and cavities were filled with rubber. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

The discovery and progress of MgCl2‐supported TiCl4 catalysts

Polyolefins represented by polyethylene (PE) and polypropylene (PP) are indispensable materials in our daily lives. TiCl₃ catalysts, established by Ziegler and Natta in the 1950s, led to the births of the polyolefin industries. However, the activities and stereospecificities of the TiCl₃ catalysts were so low that steps for removing catalyst residues and low stereoregular PP were needed in the production of PE and PP. Our discovery of MgCl₂‐supported TiCl₄ catalysts led to more than 100 times higher activities and extremely high stereospecificities, which enabled us to dispense with the steps for the removals, meaning the process innovation. Furthermore, they narrowed the molecular weight and composition distributions of PE and PP, enabling us to control the polymer structures precisely and create such new products as very low density PE or heat‐sealable film at low temperature. The typical example of the product innovations by the combination of the high stereospecificity and the narrowed composition distribution is high‐performance impact copolymer used for an automobile bumper that used to be made of metal. These process and product innovations established these polyolefin industries. The latest MgCl₂‐supported TiCl₄ catalyst is very close to perfect control of isotactic PP structure and is expected to bring about further innovations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1–8, 2004     

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     

Chemistry of olefin polymerization reactions with chromium‐based catalysts

Detailed GC analysis of oligomers formed in ethylene homopolymerization reactions, ethylene/1‐hexene copolymerization reactions, and homo‐oligomerization reactions of 1‐hexene and 1‐octene in the presence of a chromium oxide and an organochromium catalyst is carried out. A combination of these data with the analysis of ¹³C NMR and IR spectra of the respective high molecular weight polymerization products indicates that the standard olefin polymerization mechanism, according to which the starting chain end of each polymer molecule is saturated and the terminal chain end is a C?C bond (in the absence of hydrogen in the polymerization reactions), is also applicable to olefin polymerization reactions with both types of chromium‐based catalysts. The mechanism of active center formation and polymerization is proposed for the reactions. Two additional features of the polymerization reactions, co‐trimerization of olefins over chromium oxide catalysts and formation of methyl branches in polyethylene chains in the presence of organochromium catalysts, also find confirmation in the GC analysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5330–5347, 2008     

Copolymerization of ethylene with linear α‐olefins by 2‐phosphinophenolate nickel catalysts

2‐Dicyclohexyl‐ and 2‐diphenylphosphinophenol, CCHH and PPHH , react with Ni(1,5‐COD)₂ to form catalysts for polymerization of ethylene in or copolymerization with α‐olefins. The more P‐basic CCHH/Ni catalyst allows concentration‐dependent incorporation of olefins to give copolymers with isolated side groups and higher molecular weights, whereas the PPHH/Ni catalyst undergoes mainly stabilizing interactions with the olefins and leads to ethylene oligomers with no or marginal olefin incorporation. Pressure–time plots of the batch reactions show that the ethylene conversion is usually slower by catalysis with CCHH/Ni than by PPHH/Ni . The microstructure of the copolymers was determined by ¹³C NMR spectra, the number of side groups per main chain was estimated by ¹H NMR analyses. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 258–266, 2009     

Toughening of a propylene‐b‐(ethylene‐co‐propylene) copolymer by a plastomer

Several blends, covering the entire range of compositions, of a metallocenic ethylene‐1‐octene copolymer (CEO) with a multiphasic block copolymer, propylene‐b‐(ethylene‐co‐propylene) (CPE) [composed of semicrystalline isotactic polypropylene (iPP) and amorphous ethylene‐co‐propylene segments], have been prepared and analyzed by differential scanning calorimetry, X‐ray diffraction, optical microscopy, stress‐strain and microhardness measurements, and dynamic mechanical thermal analysis. The results show that for high CEO contents, the crystallization of the iPP component is inhibited and slowed down in such a way that it crystallizes at much lower temperatures, simultaneously with the crystallization of the CEO crystals. The mechanical results suggest very clearly the toughening effect of CEO as its content increases in the blends, although it is accompanied by a decrease in stiffness. The analysis of the viscoelastic relaxations displays, first, the glass transition of the amorphous blocks of CPE appearing at around 223 K, which is responsible for the initial toughening of the plain CPE copolymer in relation to iPP homopolymer. Moreover, the additional toughening due to the addition of CEO in the blends is explained by the presence of the β relaxation of CEO that appears at about 223 K. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1869–1880, 2002