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The catalytic system Ti-complex/MgCl2
... The internal donor (ID) is added to the precatalyst during its synthesis, whereas the external donor (ED) is placed in the reaction medium in combination with the Al-alkyl. The exchange of ID and ED on the catalyst surface, combined with their function of complexing with Al-alkyl, tunes the catalytic behavior and increases the stereoregularity of the produced polymer [19][20][21]. Despite this simple composition, the characterization of heterogeneous ZN catalysts is a long-established problem that several theoretical [22][23][24][25][26][27][28][29] and experimental studies [30][31][32][33][34][35][36][37] have attempted to solve [38,39]. ...
... The inner structures of the hexagonal layers are almost identical in both forms since the Van der Waals interaction keeping together the stacked MgCl 2 monolayers is weak. MgCl 2 is physically or chemically activated to obtain a support with an extensive surface area, which is indispensable for efficient catalysis [19]. In the physical route, ␣-MgCl 2 is ball-milled into nano-sized particles, known as the ␦-phase, for several hours [87][88][89]. ...
... Activated MgCl 2 , initially prepared by ball milling a mix- ture of MgCl 2 and ID, leads to the formation of many small-sized crystallites. X-ray diffracttion studies disclosed that the ␦-form of MgCl 2 , possesses a rotational disorder in the Cl-Mg-Cl triple-layer stacking and highly disordered crystalline form can be obtained by chlorination of a Grignard compound [19,85]. Focusing on the possible surface terminations of MgCl 2 , those classically considered in the literature are the (001), the (110), the (104) facets (see Fig. 4) [62,90,91], with the recent addition of the (015) facet [22]. ...
Since 1963, when Karl Ziegler and Giulio Natta were jointly awarded the Nobel Prize for their discoveries of the catalytic polymerization of olefins with Ti-chlorides and Al-alkyls, heterogeneous Ziegler-Natta (ZN) catalysts have become the main catalysts for the industrial production of polyolefins. Despite of the relevance of ZN catalysts for the large-scale production of polyolefins, a clear mechanistic understanding of these catalysts is still incomplete due to the elusive nature of the active site structures. Over the last two decades, researchers have used density functional theory (DFT) methods to clarify the polymerization mechanisms and to identify the nature of the active sites, unraveling the influence of supports, cocatalysts, and the effect of internal and external donors on the polymerization processes. Major efforts were dedicated to understanding the origin of stereoselectivity in α-olefin polymerization as well as the termination reactions mechanisms, and the role that impurities can play in heterogeneous ZN catalysis. Here, we review the DFT studies on heterogeneous ZN catalysts and suggest promising areas for future research.
... Studying the kinetics of olefin polymerization over modern highly active supported titanium-magnesium catalysts (TMC) is an important step towards understanding the mechanism of action of these systems. A number of reviews have been devoted to the analysis of the kinetic features of olefin polymerization over Ziegler-Natta catalysts [1][2][3][4][5][6]. However, some kinetic findings remain uninterpreted because of the versatility of the catalysts of this type, complex composition of the active component, several types of active centers, and changes they undergo during polymerization. ...
... According to the two-stage mechanism of the propagation reaction at catalytic polymerization proposed by Cossee [7], the propagation rate can be linearly dependent on monomer concentration and described by the first-order equation. Indeed, these dependences were observed in a large number of studies devoted to olefin polymerization over different catalysts [1][2][3][4][5][6]. However, some studies showed that a mixed (between the first and second) order of the polymerization rate with respect to ethylene is observed at low ethylene pressure [8][9][10][11][12]. ...
... The support of TMC-1 catalyst (S-1) was prepared by interaction of PhSiCl 3 with organomagnesium compound Mg 3 Ph 4 Cl 2 dissolved in diisoamyl ether [23]. The support for TMC-2 catalyst (S-2) was synthesized by interaction of the organomagnesium compound Mg 3 Ph 4 Cl 2 solution in dibutyl ether with the mixture of PhSiCl 3 and Si(OEt) 4 [24]. Support S-2 was additionally treated with a solution of diethylaluminum chloride in heptane at 40 • C and molar ratio Al/Mg = 1.5 and then washed with CCl 4 to convert adsorbed AlEt 2 Cl into AlCl 3 . ...
It was found that the observed order of the polymerization rate with respect to ethylene concentration at ethylene polymerization over two titanium-magnesium catalysts of different compositions is significantly higher than 1(1.6-2.1). The data on the effect of ethylene concentration on the number of active centers (C-p) and the propagation rate constant (k(p)) at ethylene polymerization over these catalysts were obtained by method of polymerization quenching with (CO)-C-14. An increase in ethylene concentration was found to increase the number of active centers. In some cases the increase of ethylene concentration proceeds to the narrowing of the molecular weight distribution of the resulting polyethylene and an increase in the calculated value of propagation rate constant. These effects were shown to be most pronounced at low ethylene pressure and increased concentration of an activator (AlEt3). Based on the experimental data, we proposed a scheme of reactions to explain the effects of ethylene and AlR3 concentrations on the number of active centers, the average values of propagation rate constant and molecular weight distribution of polymers produced over these multi-site catalysts.
... It is well known that the industrial polymerization temperature of MgCl 2 -supported Ziegler-Natta catalysts are around 65-80 • C. In recent years, a new supercritical olefin polymerization technology was developed, which needed higher polymerization temperature (more than 90 • C) for propylene polymerization. However, both the activity and the stereospecificity of MgCl 2 -supported Ziegler-Natta catalysts decease when the polymerization temperature rises over 85 • C [1,2]. Kojoh et al. [1] and our research group [3] had reported that in the propylene polymerization with MgCl 2 -supported Ziegler-Natta catalysts at 100 • C, the activity obtained with i-Bu 3 Al, which shows a weaker coordination and alkylation than Et 3 Al, was higher than that obtained with Et 3 Al. ...
... The use of alkylaluminiums as an activating agent is indispensable for propylene polymerization with MgCl 2 -supported Ziegler-Natta catalysts. Many investigations concerning the effect of alkylaluminiums on the propylene polymerization with Ziegler-Natta catalyst have been conducted in academic and industrial fields [2]. ...
... It was clear that an increase in polymerization temperature led not only to lower activity of catalyst but also to lower stereospecificity when alkylaluminiums were used as cocatalyst. It could be due to over reduction of titanium or to reactions of Ti-C bonds with Lewis base [2]. At 100 • C, the catalyst activity obtained with either i-Bu 3 Al or Hex 3 Al was higher than that obtained with Et 3 Al while isotacticity of PP obtained with either i-Bu 3 Al or Hex 3 Al was lower than that obtained with Et 3 Al. ...
A study of the effect of “trimethylaluminium (TMA)-depleted” methylaluminoxane (MMAO) and alkylaluminiums on propylene polymerization at high temperature in the use of a TiCl4/MgCl2/aromaticdiester-alkoxysilane catalyst has shown that, MMAO was not the actual cocatalyst. However, at low Et3Al/Ti mole ratio addition of MMAO to catalyst improved the catalyst activity and stereospecificity and the catalyst showed a high proportions of isotactic polypropylene (95%) and high activity with the mixture of MMAO and Et3Al at 100°C. Addition of MMAO reduced the molecular weights of isotactic polypropylene (iPP) but had no effect on the crystallinity of the iPPs. The appearance of β modification in the iPP obtained with Et3Al crystallization process implied that the microstructure of iPP obtained with Et3Al was different from that of iPP obtained with i-Bu3Al and Hex3Al at 100°C.
... It is well recognized that heterogeneous Ziegler-Natta catalysts contain multiple active sites, which produce PP with varying degree of stereoregurality. [1][2][3][4] Despite considerable efforts with different analysis methods, it has not been possible to determine the exact structures of the reactive active sites. If the polymer characterization can be done thoroughly enough, information on the catalyst is gained as well. ...
... It is well known that the industrial polymerization temperature of MgCl 2 -supported Ziegler-Natta catalysts are around 65-80 C. 3 In recent years, a new supercritical olefin polymerization technology was developed, which needed higher polymerization temperature (>90 C) for propylene polymerization. In our previous paper, 5 we have reported that the TiCl 4 /MgCl 2 /dibutyl phthalate(DNBP)-cylohexanemethyl dimethyloxysilane catalyst showed a high proportions of iPP and high activity with the mixture of ''TMA-depleted'' methylaluminoxane (MMAO) and Et 3 Al at 100 C and the resultant PP exhibited bimodal peaks, and one was in the vicinity of 160 C and the other was in the vicinity of 150 C. In contrast, the PPs prepared with either i-bu 3 Al or Hex 3 Al at same polymerization conditions exhibited the only peak in the vicinity of 160 C. The peak at low temperature (150 C) may result from the formation of b-PP crystal. ...
... It is well known that the industrial polymerization temperature of MgCl 2 -supported Ziegler-Natta catalysts are around 65-80 C. 3 In recent years, a new supercritical olefin polymerization technology was developed, which needed higher polymerization temperature (>90 C) for propylene polymerization. In our previous paper, 5 we have reported that the TiCl 4 /MgCl 2 /dibutyl phthalate(DNBP)-cylohexanemethyl dimethyloxysilane catalyst showed a high proportions of iPP and high activity with the mixture of ''TMA-depleted'' methylaluminoxane (MMAO) and Et 3 Al at 100 C and the resultant PP exhibited bimodal peaks, and one was in the vicinity of 160 C and the other was in the vicinity of 150 C. In contrast, the PPs prepared with either i-bu 3 Al or Hex 3 Al at same polymerization conditions exhibited the only peak in the vicinity of 160 C. The peak at low temperature (150 C) may result from the formation of b-PP crystal. 5 It has been demonstrated by researchers that the presence of the b-form within the crystalline portion of the material is beneficial to its macroscopic toughness and ductility. ...
The structure, morphology, and isothermal crystallization behaviors of polypropylene (PP) prepared with heterogeneous Ziegler-Natta catalyst at high temperature (100°C) were investigated with differential scanning calorimetry, wide-angle X-ray diffraction, temperature-rising elution fractionation, gel permeation chromatography, and 13C NMR. The results reveal that the crystalline structure changes with variation of the composition of the PP. The isotactic PP (iPP)1 prepared with Et3Al and “TMA-depleted” methylaluminoxane crystallizes from the melt in the mixtures of the and β forms, whereas each fraction obtained from pure PP1 does not show β-PP crystal at the same crystallization condition. In addition, the -PP crystal is appeared for the fractions of low mmmm%-[mmmm] (mmmm pentad content) values and molecular weight. Moreover, it was found that the iPP2 or iPP3 prepared with Hex3Al crystallizes from the melt in mixtures of the and forms, even at atmospheric pressure and for high molecular weight. The microstructure showed in the PP samples obtained at high temperature could be well explained with the shift in the alkylaluminium-donor equilibrium reactions at high polymerization temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
... Nearly all polypropylene (PP) in the world is produced using supported Ziegler-Natta catalysts [1,2]. They consist of titanium tetrachloride and a stereoregulating electron donor compound (internal donor, ID) on the surface of MgCl 2 crystallites used as the support. ...
... In propylene polymerization, these Ti-Mg catalysts (TMCs) are used in a combination with an organoaluminum cocatalyst (usually AlEt 3 ) and other stereoregulating donor (external donor, ED). The use of donors allows controlling the molecular structure (stereoregularity, molecular weight, molecular-weight distribution) of the produced polymer [1][2][3][4]. ...
... Discovery of MgCl 2 supported Ziegler-Natta (Z-N) catalyst for olefin polymerization lead to a huge progress in the polyolefin industry [1][2][3][4][5]. Heterogeneous Z-N system consists of TiCl 4 as active catalyst component, MgCl 2 based molecular adduct act as support, R 3 Al (R = methyl, ethyl, isobutyl) as co-catalyst. ...
... As discussed in our earlier reports, known amount of adduct was dissolved in 1 ml of D 2 O with THF as a reference. 1 was recorded and from the 1 H integrals the mole fraction of 2-BuOH is estimated. 2-BuOH/MgCl 2 molar ratio is found to be close to 4 which are also supported by TG-DTA analysis. ...
A new heterogeneous Ziegler-Natta (Z-N) catalyst support material, MgCl2 center dot 4(CH3CH(OH)CH2CH3) (Mg2BuOH) has been synthesized. 2-Butanol, a linear, secondary alcohol was chosen for the generation of an active MgCl2 support which results in a Z-N catalyst with TiCl4. Significant feature of this work is the formation of rod shaped molecular adduct with highly porous character. Adduct material is characterized by XRD, TG-DTA, Raman spectroscopy, solid-state NMR and SEM. Activity of the Z-N catalyst supported on Mg2BuOH for ethylene polymerization is comparable with that of commercially available heterogeneous Z-N catalyst. However, there is scope to improve the activity by optimizing textural properties.
... Of course, the presence of these species is needed to achieve an active and highly stereospecific catalyst. 42 However, activation and deactivation (mainly due to reactions of adsorbed Ti species with alkylaluminum compounds and Lewis bases) 42 are out of the scope of the present work, which only focuses on the structure of possible precursors of active sites. For the same reason, adsorption of Ti(II) species has not been considered, since Ti(II) is generally thought to be inactive in propene polymerization. ...
... Of course, the presence of these species is needed to achieve an active and highly stereospecific catalyst. 42 However, activation and deactivation (mainly due to reactions of adsorbed Ti species with alkylaluminum compounds and Lewis bases) 42 are out of the scope of the present work, which only focuses on the structure of possible precursors of active sites. For the same reason, adsorption of Ti(II) species has not been considered, since Ti(II) is generally thought to be inactive in propene polymerization. ...
Possible structures of TiCl4 molecules and TiCl3 fragments adsorbed on (110) and (100) faces of MgCl2, simulated by clusters of different size and shape, have been studied in the framework of density functional theory. For both monomeric TiCl4 and TiCl3, coordination on the (110) face is favored relative to coordination on the (100) face. TiCl3 fragments can bind together on the (100) face either forming or not Ti-Ti bonds, resulting in the formation of polynuclear TinCl3n species. The steric environment of the ending Ti atoms of such polynuclear species, with n > 2, is extremely similar to that of the C-2 symmetric sites proposed several years ago for TiCl3-based catalytic systems and presents a strict analogy with the well-established models for isospecific polymerization with catalytic systems based on C-2 symmetric metallocenes. This analogy holds also in the case of a TiCl3 fragment adsorbed on the (110) cut when both of its vicinal positions are occupied. When just one of the vicinal positions is occupied, sites of C-1 symmetry can be formed, which have two minimum-energy structures with distinct positions (inward and outward) iol the dangling chlorine. These inward and outward geometries can be expected to interconvert easily, the inward arrangement being favored.
... The extent and variety of research work dealing with the same problem reflects not only the great interest and extensive commercial applications in this area, but also the complexity of catalysts for ethylene polymerizations. Research progress concerning catalysts for ethylene polymerization has been a focus of several recent international conferences and Keii and Soga, 1990;Vandenberg and Salamone, 1992), and excellent reviews have appeared in the literature (Zakaharov and Yermakov, 1979;Karol, 1984;Hsieh, 1984;McDaniel, 1985;Nowlin, 1985;Hsieh et al., 1987;Barbe et al., 1987;Tait, 1989;Kryzhanovskii and Pranchev, 1990;Dusseault and Hsu, 1993). Catalyst development plays a vital role in the polymerization of ethylene, particularly in successful gas phase polymerization processes (Karol, 1983). ...
... 1. MgClz has crystalline forms similar to those of Tic13 (conventional Ziegler-Natta catalyst) (Chien, 1987;Barbe, 1987;Dusseault and Hsu, 1993). This distinct feature suggests that MgClz should have the ability to mimic the structure of active Tic13 and the ability to efficiently incorporate TiC14. ...
A review of relevant macroscopic and microscopic processes of gas phase ethylene polymerization, both chemical and physical, is given. The commercial technology development of gas-phase ethylene polymerization processes is illustrated through a selective survey of the patent literature. Both advantages and disadvantages of gas phase polymerization processes are addressed, and the challenges of laboratory studies of gas phase polymerization are also outlined. Physicochemical phenomena of ethylene polymerization using heterogeneous catalysts are discussed, including examination of catalyst preparation, polymer morphological development, and elementary chemical reactions. Metallocene-based catalysts and their kinetic performance for olefin polymerizations are also discussed. The current state of the art for reactor modeling of polymerization rate, molecular weight development, reactor dynamics, and resin grade transition strategies is illustrated on the basis of the most recent academic studies. Finally, relationships between resin properties and polymer microstructures as well as characterization methods are described briefly. In particular, temperature-rising elution fractionation technology is emphasized for characterization of ethylene copolymers. The fundamental issues involved in gas phase ethylene polymerization and their interrelationships are also discussed in some detail.
... At the same hydrogen concentration, the isotactic index of polypropylene tends to increase with the increase of polymerization temperature. Since the more isoselective-active sites produce higher molecular weights polypropylenes [23], the MFR of produced polypropylene would decrease, and polymerization activity would increase with increasing II. The polymerization activity of the group with nonisothermal prepolymerization increased with increasing II, but the MFR increased after the temperature was raised from 70°C to 80°C. ...
The effects of prepolymerization, temperature, and hydrogen concentration on propylene bulk polymerization with a commercial Ziegler-Natta catalyst were investigated, and the apparent polymerization rate constants were estimated by varying reaction temperatures, hydrogen partial pressures, and polymerization methods. It was shown that prepolymerization has different effects on the polymerization rate and isotacticity of the polymer; without prepolymerization, the polymerization rate and isotacticity reach their maximum at 70°C and 80°C, respectively, whereas the polymerization rate and isotacticity with prepolymerization increase with the polymerization temperature in the range of 50-80°C. Moderate prepolymerization time reduced the fine fraction while increasing polymerization rate and isotacticity. Appropriate prepolymerization technique can increase mass transfer performance and fragmentation, which is a promising way to improve polymerization rate, isotacticity index, and fine fraction. Otherwise, insufficient prepolymerization or excessive prepolymerization causes prepolymer particle fragmentation.
... As the most significant industrial catalysts of polyolefin production, heterogeneous Z-N catalysts present satisfactory stereoselectivity and particle morphology controllability. [8][9][10] Alkylaluminium as cocatalyst plays significant roles in olefin polymerizations with heterogeneous Z-N catalysts. The important roles of the cocatalyst include TiCl 4 reduction to lower valence Ti species, alkylation, [11][12][13][14][15] reversible complexion and absorption reactions between aluminium compounds and metal atoms (Mg, Ti) of the catalyst surface causing transformation in the stereoselectivity as well as activity of multiple active sites. ...
Copolymerizations of isoprene (Ip) and butadiene (Bd) in different Bd/Ip feed ratios were carried out using the heterogeneous TiCl4/MgCl2 type Ziegler–Natta (Z‐N) catalysts activated by trimethylaluminium (AlMe3), triethylaluminium (AlEt3), triisobutylaluminium (Al(i‐Bu)3) or tri‐n‐octylaluminium (AlOct3). Monomer reactivity ratios of Ip and Bd (rIp, rBd) in the copolymerizations were calculated by the Kelen–Tödüs method and then instantaneous compositions of the copolymers were theoretically acquired based on the Mayo–Lewis equation. The effects of alkylaluminiums on copolymerization activity, copolymer microstructure, comonomer incorporation, monomer reactivity ratios and copolymer instantaneous composition were investigated. Using AlEt3 led to higher copolymerization activity and trans‐1,4 stereoselectivity compared with other trialkylaluminiums. AlOct3 with bulky n‐octyl groups showed a higher Bd monomer reactivity ratio. The theoretical copolymer composition drift based on the Mayo–Lewis equation was in good coincidence with the experimental data measured by real‐time ¹H NMR during the steady polymerization stage. The nature of the discrepancy between the theoretical and measured copolymer compositions obtained in the initial polymerization stage is discussed in detail. © 2021 Society of Industrial Chemistry.
... These catalysts are modified with electron-donating organic compounds to increase catalyst stereospecificity. These stereoregulating additives are used both during TMC synthesis (internal electron donor D 1 ) and during propylene polymerization (external donor D 2 ) [2][3][4][5][6]. In the latter case, an external donor D 2 is added together with an organoaluminum cocatalyst (usually triethylaluminum, TEA). ...
The effect of a set of methoxy- and ethoxysilanes as external donors (ED) on propylene polymerization in liquid monomer with the supported titanium–magnesium catalyst (TMC) and on properties of the produced polypropylene (PP) are studied. Addition of the studied donors to the polymerization system significantly increases the PP isotacticity compared to polymerization over TMC without ED (up to 92–98% vs. 66%, respectively). It is found that activity and stereospecificity of the catalytic system, as well as the molecular weight of the produced PP, decline as the number and size of alkoxy groups increase and the size (branching) of alkyl substituents decreases. Bulky substituents in alkoxysilanes have a positive effect on activity and stereospecificity of TMC. However, the double bond in the substituent moiety reduces the catalyst activity. Nitrogen atom in the substituent (with the same alkoxy groups) increases isotacticity and crystallinity of PP, its flexural modulus and strength characteristics. Varying electron donors with different number and size of alkoxy groups and different substituents (aliphatic, aromatic, alicyclic, amino, and vinyl) at silicon atom allows one to control the catalyst activity and isotacticity, as well as the molecular and thermal characteristics and impact strength properties of PP.
... An early version of supported catalyst for PP production was prepared by the reaction of MgCl 2 , TiCl 4 , and ethylbenzoate (32). This type of catalyst system containing ethylbenzoate as Di was used in combination with a second aromatic ester such as methyl p-toluate as De (33). ...
First invented in 1953, Ziegler–Natta catalysts have been used widely in the industrial production of polyolefins and other important polymers since the 1960s. In recent years, polymers synthesized with these catalysts account for more than 30% of the total production of polymers. This article briefly introduces the history and main developments of Ziegler–Natta catalysts and explains their preparation, composition, and mechanism of the catalysis process. Particular emphasis is put on the currently more important MgCl2‐supported Ziegler–Natta catalysts. Main features of the olefin polymerization with MgCl2‐supported Ziegler–Natta catalysts are presented, including the formation and structure of active sites, main reactions with the active sites, origin of stereospecificity, reaction kinetics, and morphology of the nascent polymer particles. The main olefin polymerization processes with these catalysts are also briefly discussed.
... Over the last decade, originating from the simple TiCl 4 crystal [1], ZNc has been developed based on the use of MgCl 2 as a support for TiCl 4 [2]. The active sites in such systems are formed by treating the adsorbed TiCl 4 molecules with an alkylating reducing species, such as Al(Et) 3 in which Et denotes ACH 2 CH 3 [3][4][5][6]. Since the TiCl 4 /Al(Et) 3 catalytic system was originally discovered, polyethylene (PE) has had an enormous impact in the petrochemical industry. ...
Density functional theory (DFT) calculations have been carried out to investigate the ethylene insertion pathway using a Ziegler-Natta catalyst in the absence and presence of electron donor (ED) systems on the (110) MgCl2 surface. The coadsorptions of four different EDs i.e. Si(OEt)mCln (m + n = 4) were investigated. The presence of Si(OEt)4 on the (110) MgCl2 surface with the preferential bidentate mode was found to have the strongest adsorption energy (ΔEads). The potential energy surface (PES) map indicated that the reaction mechanism of the ethylene insertion into the Ti-C bond on the (110) Mg13Cl26.TiCl3-CH2CH3 surface is pseudo-concerted. As the differences in the intrinsic activation energies (ΔEa) obtained from all systems are so small, this energy cannot be used to fully explain the significant changes in the rates of the ethylene insertion reaction observed when an ED is employed. Here, the apparent activation energy (ΔΔEaa) was calculated using the PBE functional and the 6-31G(d, p) basis set for C, H, O, Mg and Cl, and the LANL2DZ basis set with an ECP function for the Ti atom. All EDs presented in this work in the ethylene insertion reaction can significantly reduce the apparent energy barrier when compared to an absence of any ED system. The obtained ΔΔEaa for the four ED complexes were found to decrease in the following order: SiOEtCl3 > Si(OEt)2Cl2 > Si(OEt)3Cl > Si(OEt)4. The obtained data lead to the conclusion that Si(OEt)4 is the most suitable ED to increase the productivity of PE in the presence of alkoxysilane.
... It is well known that the different fractions of the ZN iPP samples, characterized by different microstructures, can be separated by the conventional methods of extraction in boiling solvents [21,22]. The commercial iPPEt copolymers were fractionated and the different fractions were characterized [23]. ...
Isotactic polypropylene-based (iPP) materials find large applications for the food packaging. In this article the structure, thermal and mechanical properties of some commercial grades of ethylene/propene copolymers produced by heterogeneous Ziegler-Natta (ZN) catalysis, have been characterized. These grades can be potentially used for manufacturing food containers. However, despite the desired performances in terms of mechanical and optical properties, we found that the samples exceed the overall migration limit set by the EU Directive into isooctane, used as fatty food simulant. The migrating species are highly defective copolymer chains with low molecular mass and high ethylene content. The migration is intrinsically related to the presence of fractions generated by the heterogeneous multisite surface of the ZN catalysts. A simple chemical route to allow the iPP-based materials to fall within the overall migration limit is proposed.
... Most of the world's polypropylene is currently pro duced with titanium containing Ziegler-Natta catalysts [1,2]. High performance catalytic systems based on tita nium chlorides deposited on magnesium dichloride have found the widest industrial application in synthesizing polypropylene with trialkylaluminum and electron donor compounds, TiCl 4 /D 1 /MgCl 2 + AlR 3 /D 2 (where D 1 and D 2 denote internal and external donors, respec tively) [3][4][5][6][7][8][9][10][11][12][13][14][15]. During polymerization in liquid mono mer, so called fourth generation Ziegler-Natta cata lysts yield 30-60 kg of polymer per 1 g catalyst with polypropylene isotacticity above 96 wt % [16]. ...
A comparative study of propylene polymerization in liquid monomer is performed under laboratory conditions using the IK-8-21 Ti-Mg catalyst designed at the Boreskov Institute of Catalysis and imported industrial catalysts (conditionally labeled TMC-1, -2, and -3). The activity and stereospecificity of the catalysts are estimated along with properties of the resulting polypropylene (granular composition and physicomechanical characteristics). It is shown that the IK-8-21 catalyst is not inferior to imported counterparts in terms of catalytic properties in the synthesis of polypropylene. The polypropylene powder formed on IK-8-21 is homogeneous and has good morphology. The physicomechanical characteristics of polypropylene synthesized on the domestic IK-8-21 catalyst are similar to those for polypropylene prepared with the imported TMK-1 catalyst. © Pleiades Publishing, Ltd., 2014. © I.I. Salakhov, A.Z. Batyrshin, S.A. Sergeev, G.D. Bukatov, A.A. Barabanov, A.G. Sakhabutdinov, V.A. Zakharov, Kh.Kh. Gilmanov, 2014.
... They are sustainable materials because of their pure hydrocarbon structures from natural oils and are further being useful as resources for energy or hydrocarbon substrates. 1 The recent Asian crisis of the plasticizer (commonly phthalates) within food packages, which can potentially cause harm to the endocrine, reproductive and respiratory systems of humans, 2 raised some concerns regarding the use of polyolefins produced by Ziegler-Natta catalytic systems possessing phthalate donors. 3 In addition, processing lubricates for the engineering of plastics and alloys are comprised of linear polyethylenes, which are required to possess relatively lower molecular weights (usually in the tens of thousands) and narrow molecular weight distributions. These specific polyethylenes could be produced by metallocene 4 or half-titanocene catalytic systems. ...
A series of cobalt(II) dichloride complexes ligated by 2-[1-(2,4-dibenzhydryl-6-methylphenylimino) ethyl]-6-[1-(arylimino)ethyl]pyridines was synthesized and characterized by FT-IR spectroscopy and elemental analysis. The molecular structure of the representative complex Co4 (R1 = Me, R2 = Me) was confirmed as pseudo square-pyramidal geometry at cobalt by single-crystal X-ray diffraction. Upon treatment with the co-catalysts MAO or MMAO, all cobalt pre-catalysts exhibited high activities up to 1.81 × 107 g PEmol−1(Co) h−1 in ethylenepolymerization, and produced polyethylene products with molecular weights in the tens of thousands and narrow molecular weight distributions. The influence of the reaction parameters and nature of the ligands on the catalytic behavior of the title cobalt complexes was investigated.
... Modem heterogeneous Ziegler-Natta catalysts for the polymerization of propylene are composed of titanium tetrachloride on a magnesium dichloride support (Pino & Mulhaupt, 1980; Kashiwa, 1980; Barbe, Cecchin & Noristi, 1987; Miyatake, Mizunuma & Kakugo, 1990). The stereospecificity of the basic catalyst can be improved by internal donors such as dialkyl phthalates and external donors such as phenyl-and alkylalkoxysilanes. ...
TiCl4 reacts with (iC4H9)2C(CH2OCH3)2 in n-heptane forming the monomeric complex [TiCl4(C13H28O2)] which is converted into the oxygen-bridged dimeric structure [TiCl3(C13H28O2)]2O in the presence of H2O. In the dimeric structure the coordination of each Ti atom is octahedral. The angle between the bridging O atom and the Ti atoms is 163.4 (4)-degrees.
... However, the precise control of olefin polymerization with a conventional heterogeneous Ziegler-Natta catalyst has been considered difficult for a long time because of inevitable side reactions, such as catalyst deactivation and various transfer reactions. [1][2][3][4][5] The unfavorable side reactions and short-lived growing polymer chain are also the main reasons for the difficult synthesis of a real olefin block copolymer having a chemical linkage between two different segments. ...
A high-pressure-type stopped-flow polymerization system was developed for the production of a real block copolymer, polypropene-block-poly(ethene-co-propene), having a variable molecular weight. The preliminary homopolymerization experiments of propene at 1−6 atm for 0.1 s with an MgCl2-supported Ziegler catalyst and TEA indicated that the polymer yield and molecular weight of the resulting polypropene were proportional to the monomer concentration in the system. This indicates that the catalyst activity is constant and the unfavorable side reactions can be negligible, i.e., independent of the monomer pressure. The higher propene and ethene concentrations, which could be regulated by the pressures of the vessels in the apparatus, were found to induce a higher molecular weight of the resulting block copolymer without a significant change in the molecular weight distribution and microstructure. The CFC, DSC, and AFM analyses results indicated that the increased molecular weight had an influence only on the lamellar thickness but had no effect on the crystallinity and its distribution of the block copolymer.
... According to the kinetic curves of Fig. 1, these catalysts present a ''deactivation'' type behaviour [20], where speed decline is attributed mainly to a chemical deactivation of the active centres through time. It can be seen the great difference of the polymerization speeds for the three analysed catalysts. ...
This paper is a comparative study of the performance of TiCl 4 catalysts supported on recrystallized MgCl 2 through different techniques for the polymerization of ethylene, propylene and ethylene–propylene copolymers. MgCl 2 was dissolved in 1-hexanol and recrystallized through solvent evaporation, quick cooling and precipitation with SiCl 4 . The effect of the recrystallization conditions during the catalyst preparation on the chemical composition of catalysts was discussed with the help of IR spectroscopy. The variations of dealcoholation levels due to the different recrystallization techniques highly influenced the catalytic activity. The catalyst obtained through SiCl 4 recrystallization was not only the most active, but it also showed the highest isotacticity indexes for propylene polymerization.
... Over the years, Ziegler-Natta catalysts have evolved from simple TiCl 3 crystals into the MgCl 2 /TiCl 4 /donor systems used today, where the donor is a Lewis base that can be added during catalyst preparation (the so-called internal donor). [4,74] Among donors, 1,3-diethers, [75] aromatic esters (benzoates and phthalates in particular) [76] and, recently, aliphatic esters (succinates in particular) have been shown to be particularly effective. [77] Catalyst activation requires the addition of alkylating reducing species (AlEt 3 is generally used), possibly mixed with a second electron donor (the so-called external donor (ED)), usually an alkoxysilane or, more recently, a succinate. ...
ENGLISH ABSTRACT: The crystallization of polyolefins is an important parameter in determining the properties of such materials. The crystallization phenomenon generally depends on the molecular symmetry (tacticity) and molecular weight of the material. In this study, a series of polypropylenes was prepared using heterogeneous MgCl2-supported Ziegler catalysts with two different external donors, diphenyldimethoxysilane (DPDMS) and methyl-phenyldimethoxysilane (MPDMS), and two different homogeneous metallocene catalysts, racethylene- bis(indenyl) zirconium dichloride, Et(Ind)2ZrCl2 (EI), and rac-ethylene-bis(4,5,6,7- tetrahydro-1-indenyl) zirconium dichloride, Et(H4Ind)2ZrCl2 (EI(4H)). Molecular hydrogen was used as terminating agent. In order to establish a correlation between the molecular weight and the crystallization of these polymers, fractionation of the materials according to crystallizability was performed by means of temperature rising elution fractionation (TREF). This affords the opportunity of blending materials of different molecular weights but similar symmetry. These materials were characterized using various analytical techniques: differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), 13C nuclear magnetic resonance spectroscopy (13C-NMR), high temperature gel permeation chromatography (HT-GPC) and Fourier-transform infrared spectroscopy (FT-IR). DSC was used to study the bulk crystallization of different polypropylene blends, most of which showed only one melting peak. The latter is usually associated with a high degree of cocrystallization. Turbidity analysis of the different polypropylene polymers, obtained using solution crystallization analysis by laser light scattering (SCALLS), provided good crystallization information – similar to that provided by crystallization analysis fractionation (CRYSTAF) and TREF. It was also possible to differentiate between polypropylenes with similar chemical structure but different tacticity and molecular weight. SCALLS results also showed that the blends of different isotactic polypropylene polymers were miscible and cocrystallization had occurred, whereas, the blends of syndiotactic polypropylene and different isotactic polypropylenes were not miscible and some interaction between phases had occurred. Optical microcopy (OM) and scanning electronic microscopy (SEM) were used to study the morphological properties of different isotactic polypropylenes. Results revealed a welldefined and large spherulitic morphology of mixed a1 (disordered) and a2 (ordered) crystal form structures. OM and SEM images also clearly showed an effect of molecular weight and tacticity on the crystal structure of the different polypropylene samples. Finally, various homopolymers and blends were studied to investigate the effect of molecular weight on the mechanical properties of these materials. This was done using microhardness testing and dynamic mechanical analysis. AFRIKAANSE OPSOMMING: Die kristallisasie van poliolefiene is ‘n belangrike faktor wat die eienskappe van hierdie tipe materiale bepaal. In die algemeen hang kristallisasie af van die molekulêre simmetrie (taktisiteit) en molekulêre massa van die materiaal. ‘n Reeks polipropilene is berei deur gebruik te maak van heterogene MgCl2-ondersteunde Ziegler-kataliste met twee verskillende elektron donors, difenieldimetoksisilaan (DPDMS) en metielfenieldimetoksisilaan (MPDMS), en twee verskillende homogene metalloseenkataliste, rac-etileen-bis(indeniel) sirkoniumdichloried, Et(Ind)2ZrCl2 (EI), en rac-etileen-bis(4,5,6,7-tetrahidro-1-indeniel) sirkoniumdichloried, Et(H4Ind)2ZrCl2 (EI(4H)). Molekulêre waterstof is gebruik as termineringssagent. Ten einde ‘n verband te bepaal tussen die molekulêre massa en kristallisasie van hierdie polimere is hulle gefraksioneer op die basis van hulle kristallisseerbaarheid deur gebruik te maak van temperatuurstyging-elueringsfraksionering (TREF). Deur hierdie tegniek verkry ons materiale van verskillende molekulêre massa maar met dieselfde taktisiteit wat ons kan vermeng. Verskeie tegnieke is gebruik om hierdie materiale te karakteriseer: differensiële skandeerkalorometrie (DSC), wyehoek X-straal diffraksie (WAXS), 13C-kernmagnetiese resonansspektroskopie (13C-KMR), hoë-temperatuur gelpermeasiechromotagrafie (HT-GPC) en Fourier-transform-infrarooispektroskopie (FT-IR). DSC is gebruik om die vaste-toestand kristallisasie van verskeie vermengde polipropilene te bestudeer., en net een smeltpunt is in meeste gevalle waargeneem. Laasgenoemde word gewoonlik verbind met ‘n hoë mate van kokristallisasie. Oplossingkristallisasie analise, dmv laserligverstrooiing (SCALLS), is gebruik om die turbiditeit van die verskillende polipropileen kopolimeervermengings te bepaal. Goeie inligting aangaande die kristallisasie in oplossing – soortgelyk aan dié wat dmv die kristallisasie-analise-fraksioneringstegniek (CRYSTAF) en TREF bepaal is, is verkry. Dit was ook moontlik om te onderskei tussen polipropilene met soortgelyke chemiese strukture maar verskillende taktisiteit en molekulêre massas. SCALLS data het ook getoon dat die vermengings van verskeie isotaktiese polipropileen polimere versoenbaar was en dat kokristallisasie plaasgevind het, terwyl vermengings van sindiotaktiese polipropileen en verskeie isotaktiese polipropilene nie versoenbaar was nie en dat ‘n mate van fase-skeiding plaasgevind het. Optiese mikroskopie (OM) en skandeer-elektronmikroskopie (SEM) is gebruik om die morfologiese eienskappe van verskillende isotaktiese polipropilene te bepaal. Goed gedefineerde en groot sferulitiese morfologie van gemengde a1 (onordelike struktuur) en a2 (ordelike struktuur) kristal-strukture is waargeneem. OM en SEM beelde het ook gewys dat molekulêre massa en taktisiteit ‘n effek het op die kristalstruktuur van die verskillende polipropileenmonsters. Laastens is die meganiese eienskappe van ‘n verskeidenheid homopolimere en vermengde materiale bestudeer, deur gebruik te maak van mikro-hardheid metings en dinamiesmeganiese analise (DMA). Thesis (PhD (Chemistry and Polymer Science ))--University of Stellenbosch, 2011.
Magnesium dichloride, titanium tetrachloride, and triethyl aluminum are essential components in the Ziegler-Natta catalysts for olefin polymerization. We report a systematic computational investigation (M06-2X/def-TZVP level of theory, thus accounting for dispersion) of the thermodynamics of a sequence of catalytic reactions leading to ethylene polymerization in the absence of electron donors. The reactions are explored for a series of TiCl4-adsorbed magnesium dichloride clusters as a function of the adsorption site, involving (104)- and (110)-type ideal edge sites alongside with corners representing defect sites. The reactions comprise alkylation of TiCl4, reduction from Ti(IV) to Ti(III) and Ti(II), ethylene π-complexation to Ti(III), and chain growth. The polymerization process as a whole is shown to be strongly exergonic for all adsorption sites, with coordination numbers of the site mainly contributing to the reduction and π-complexation energies.
MgCl2 supported Ziegler–Natta (Z–N) catalysts have emerged as the most exciting chemical process for polyolefin technology, which is responsible for the production of ∼150 million tons of polyolefin (polyethylene and polypropylene) per annum. However, fundamental chemistry of Z–N catalysts is not fully understood yet due to their multi-component nature as well as heterogeneous systems. Therefore, in this review, we have highlighted the chronological development of a heterogeneous Z–N catalyst and its polymerization (ethylene, propylene and 1-butene) process including termination steps. Then, we have discussed different structural and chemical aspects of the catalyst support, catalytically active sites, cocatalyst, internal/external electron donors and their different combinations. In the last two decades, density functional theory (DFT) has been employed in Z–N systems to strengthen the experimental work as well as to understand mechanistic aspects of Z–N systems. Future directions of Z–N catalysts have also been discussed.
The majority of post-consumer plastic waste is not recycled. Impediments to the recycling of commodity polymers include separation, impurities and degradation of the macromolecular structures, all of which can negatively affect the properties of recycled materials. An attractive alternative is to transform polymers back into monomers and purify them for repolymerization — a form of chemical recycling we term chemical recycling to monomer (CRM). Material recycled in this way exhibits no loss in properties, creating an ideal, circular polymer economy. This Review presents our vision for realizing a circular polymer economy based on CRM. We examine the energetics of polymerization and other challenges in developing practical and scalable CRM processes. We briefly review attempts to achieve CRM with commodity polymers, including through polyolefin thermolysis and nylon 6 ring-closing depolymerization, and closely examine the recent flourishing of CRM with new-to-the-world polymers. The benefits of heterocycle ring-opening polymerization are discussed in terms of synthetic control and kinetically accessible polymer-backbone functionality. Common chemical and structural characteristics of CRM-compatible ring-opening-polymerization monomers are identified, and the properties, benefits and liabilities of these recyclable polymers are discussed. We conclude with our perspective on the ideals and opportunities for the field.
Polypropylene (PP) is one of the most widely used polymers. In this paper, three types of PPs including random PP, impact PP, and impact PP with high clarity, were prepared through a 75 kg/h pilot-scale Spheripol II process. The three produced PPs were produced by the selection or combination the two loops and gas phase reactor and controlling the comonomer and hydrogen concentrations. The three prepared PPs then were pelleted with the clarified nucleating agent NX 8000 and tested for mechanical, thermal, and optical properties. Their molecular structures and rubber phase size were also investigated by GPC, 13C NMR, temperature rising elution fractionation (TREF), XRD, SEM analysis, etc. The results showed that the random PP (PP-1) and the impact PP with high clarity (PP-3) obtained excellent optical transparency with a haze of 12.5% and 13.5% due to their small rubber phase size (roughly ≤ 100 nm), while the impact PP (PP-2) obtained bad transparency with a haze of 98.8% due to the large rubber phase size (about 1 μm) caused by the poor thermal compatibility with the PP matrix. The rubber phase content and ethylene/propylene sequence distributions of the three PPs varied much and resulted in different impact strengths and stiffness properties. PP-2 had a high impact strength of 14.5 kJ/m2 due to the rubber phase generated in the gas phase reactor. Except for the optical transparency, PP-3 gained stiffness and toughness, with 914 MPa of flexural modulus and 25.1 kJ/m2 of impact strength due to the unique molecular structure of its rubber phase.
The most commonly used cocatalyst species in Ziegler-Natta catalysts are aluminium alkyls. In this study we aim to find the interaction between aluminium centres of these activators and other components in the ZNC system. Initially we look at binary systems of Al-alkyl/MgCl2 and ternary systems of Al-alkyl/MgCl2/TiCl4, followed by donor containing systems. The aluminium alkyls prove to be very reactive species and only in the case of trimethylaluminium the alkyl is strongly present in the sample. This species appears to convert, however, over time. ¹H NMR proves to be an efficient method to detect the presence of the Al-alkyl species. The use of high magnetic field strengths and ²⁷Al MQMAS NMR alleviates signal overlap and gives insight in the dominant line broadening mechanisms thus providing an in-depth view of the cocatalyst. Various Al species with different coordinations can be identified in the samples. The heterogeneity of the samples turns out to have a larger effect on the ²⁷Al NMR spectra than the quadrupolar interaction, which argues against the presence of highly distorted sites with mixed coordinations. Nevertheless for the samples indicating the presence of alkyls in the ¹H NMR spectra, we observe an aluminium site at 97 ppm in the ²⁷Al spectra that might be coordinated to an organic group.
Polypropylene is one of the fastest growing plastic materials1. The main reason for its high growth rate is the wide variety of properties1,2 which can be achieved for example by incorporating comonomers to give copolymers with decreased melting points down to 120 °C or to give impact modified polypropylenes with rubber contents up to 60% directly synthesized in the reactor3.
Many polyolefins are produced by catalyzed olefin polymerization over solid catalysts. A variety of processes are currently in use including loop, continuous-stirred tank, horizontal stirred bed and fluidized-bed technologies. In each of these continuous processes, the reactor residence time distribution is unique and affects the resulting distribution of polymer properties. In this paper we present a population balance modeling approach for modeling multistage olefin polymerization processes using catalyst residence time as the main coordinate. The catalyst may possess a broad particle size distribution and contain multiple active sites with a comprehensive kinetic scheme involving multiple monomers. Diffusion limitations during reaction may also be a consideration. A variety of reactor systems can be modeled each with unique residence time distributions and having different internal and external residence time distribution. In addition, the modeling allows the consideration of particle size selection effects within the process. These effects are implemented in a model of a fluidized-bed reactor. The population balance model is illustrated with examples of propylene polymerization in the four major commercial processes listed above, with a high activity catalyst. Comparisons of total production capacity, catalyst yield distribution, polymer particle size and porosity distribution are made. It is found that significant differences exist between the different industrial processes. It is also found that the performance of the fluidized-bed reactor is highly sensitive to fluidization conditions, particle size selection effects and the catalyst particle size distribution. Differences in product quality are discussed and issues such as fines generation and particle sticking are addressed.
Commercially important impact polypropylene is usually produced in a cascade of reactors in series using a solid catalyst. The product is made in situ by the addition of an ethylene-propylene copolymer phase to isotactic polypropylene. Since all industrial processes are continuous in nature, reactor residence-time distributions imply a natural distribution of polymer properties from polymer particle to particle as they exit the process. In this paper we apply the methods of population balances to impact polypropylene produced in several industrially significant multistage processes. The presence of monomer diffusion, due to the changing morphology of the growing copolymer particles is also included. It is shown that catalyst residence-time distribution has a significant effect on the copolymer content, ethylene content and total yield distribution of the product. The performance of each commercial process is compared, and issues such as the role of diffusion and particle sticking in the reactor are discussed.
In this work a new model for the polymerization of olefins in a loop reactor is presented. The reactor is modelled as two tubular reactors interconnected. In contrast to the traditional equivalent CSTR approach, this model allows important effects such as recycle rate, axial dispersion and heat transfer to be investigated. Some simulation results are presented.
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