No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
In Ziegler–Natta Catalysts and Polymerizations
Abstract
Incluye bibliografía e índice
... However, this high value of the Ziegler-Natta catalysts and the consequent simple and regular structure of polyolefins macromolecules is more a myth than a reality. The structure of macromolecules of polyolefins and copolymers of olefins is, instead, more complex owing to the intricate nature of the active Ziegler-Natta catalytic species [1][2][3]. ...
... Solid particles of Ziegler-Natta catalysts [3][4][5][6] consists of activated TiCl 3 , or of active Ti compounds (generally TiCl 4 ) supported on magnesium chloride in combination with an aluminum alkyl as co-catalyst and suitable Lewis bases added to the co-catalyst (external donors) and/or to the solid catalyst (internal donors) [1,3,4,6].The function of donors has been object of deep investigations and their structure has been designed to increase catalyst activity and stereoselectivity [3,4]. The intricate structure of Ziegler-Natta catalysts is related to their intrinsic multi-site nature, that is the presence of different active catalytic sites on the surfaces of catalyst particles that may produce in homopolymerization different macromolecules characterized by different stereoregularity and molecular mass and a non-random distribution of defects. ...
... The heterogeneous samples are generally separable by extraction in solvents having different boiling temperatures or by fractional crystallization at 25 • C from solution in xylene at 130 • C [1][2][3], and fractions containing chains grown from different sites having different molecular mass and stereoregularity and, in the case of copolymers, different comonomer concentrations may be generally separated. For polyolefin homopolymers, the insoluble more crystalline fraction contains, generally, highly isotactic chains, whereas the more soluble fractions contain poorly isotactic (less crystalline) and atactic (amorphous) chains [1][2][3][4][5][6]. ...
... Since its discovery and development in the 1950s and 1960s, Ziegler-Natta polymerization catalysis has undergone various empirical optimizations regarding the composition of the catalyst mixtures applied [1][2][3]. While the actual active (bimetallic) catalysts/sites have remained elusive and are subject of ongoing research, the properties of the industrially fabricated polymer products have been tailored by choice of component concentrations and additives [1,[4][5][6]. ...
... Since its discovery and development in the 1950s and 1960s, Ziegler-Natta polymerization catalysis has undergone various empirical optimizations regarding the composition of the catalyst mixtures applied [1][2][3]. While the actual active (bimetallic) catalysts/sites have remained elusive and are subject of ongoing research, the properties of the industrially fabricated polymer products have been tailored by choice of component concentrations and additives [1,[4][5][6]. ...
... 'Ziegler Mischkatalysatoren' gain their exceptional reactivity through the cooperativity of a transition metal component and an organoaluminum(magnesium) activator [1][2][3][4][5]. Industrial 1,3-diene polymerization processes also take advantage of Ziegler-type catalysts and ternary mixtures like carboxylate-based Nd(O 2 CR) 3 /Et 3 Al 2 Cl 3 /iBu 2 AlH (1:1:8) or Nd(O 2 CR) 3 /Et 3 Al 2 Cl 3 /AliBu 3 (1:1:30) [6] proved superior to ternary 'no-less-complex' d-transition metal-based catalyst systems in terms of activity and stereospecificity issues [6][7][8][9]. ...
During the past two decades homoleptic tetramethylaluminates of the trivalent rare-earth metals, Ln(AlMe4)3, have emerged as useful components for efficient catalyst design in the field of 1,3-diene polymerization. Previous work had focused on isoprene polymerization applying Ln(AlMe4)3 precatalysts with Ln = La, Ce, Pr, Nd, Gd and Y, in the presence of Et2AlCl as an activator. Polymerizations employing Ln(AlMe4)3 with Ln = La, Y and Nd along with borate/borane co-catalysts [Ph3C][B(C6F5)4], [PhNMe2H][B(C6F5)4] and [B(C6F5)3] were mainly investigated for reasons of comparison with ancillary ligand-supported systems (cf. half-sandwich complexes). The present study investigates into a total of eleven rare-earth elements, namely Ln = La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Y, Er and Lu. A full overview on the polymerization behavior of Ln(AlMe4)3 in the presence of perfluorinated borate/borane cocatalysts and R2AlCl-type activators (R = Me, Et) is provided, probing the monomers isoprene and 1,3-butadiene (and preliminary ethylene). Virtually complete cis-1,4-selectivities are obtained for several catalyst/cocatalyst combinations (e.g., Gd(AlMe4)3/Me2AlCl, >99.9%). Insights into the ‘black box’ of active species are obtained by indirect observations via screening of pre-reaction time and cocatalyst concentration. The microstructure of the polydienes is investigated by combined 1H/13C NMR and ATR-IR spectroscopies. Furthermore, the reaction of [LuMe6(Li(thf)x)3] with AlMe3 has been applied as a new strategy for the efficient synthesis of Lu(AlMe4)3. The solid-state structures of Gd(AlMe4)3 and Tb(AlMe4)3 are reported.
... Further comparisons within the NHC ligand class were drawn between aryl and alkyl groups. Synthesis of the six different Al(III) hydrides (1)(2)(3)(4)(5)(6) used in this study ( Figure 2) were prepared according to literature procedures and then subsequently trialed in dehydrocoupling catalysis. ...
... Volatiles were removed under reduced pressure to leave a colorless oil (0.83 g, 73%). 1 ...
... This was subsequently washed with 3 × 10 mL of n-hexane to yield a colorless solid, 80 mg, 67% yield. 1 ...
The catalytic dehydrocoupling of amine–boranes has recently received a great deal of attention due to its potential in hydrogen storage applications. The use of aluminum catalysts for this transformation would provide an additional cost-effective and sustainable approach towards the hydrogen economy. Herein, we report the use of both N-heterocyclic imine (NHI)- and carbene (NHC)-supported Al(III) hydrides and their role in the catalytic dehydrocoupling of Me2NHBH3. Differences in the σ-donating ability of the ligand class resulted in a more stable catalyst for NHI-Al(III) hydrides, whereas a deactivation pathway was found in the case of NHC-Al(III) hydrides.
... The Ziegler-Natta catalyst based polymerization method was much improved and matured method compared to old sodium based method and due to streospecificity it is currently most popular. [7] Chemistry of Current Manufacturing Process: Butadiene rubber is the homopolymer of 1,3-butadiene (CH 2 =CH-CH=CH 2 ) monomer which is basically a dieneor diolefin. It is the double bonds of this diene moleculein 1 and 3 carbon positions which make this molecule active in polymerization process in presence of catalyst. ...
... [14] Trends and R&D Efforts: In last three-four decades, main focus of research was identifying good catalyst and co-catalysts for high conversion of monomer, low gel formation, desirable microstructure, role of moisture in polymerization process as promoter, activator as well as deactivator, and control of molecular weight through chain transfer agents. [7,9,21,22,24] In last two decades, people tried to monitor the quality of continuous polymerization process. One major step towards this direction is on line quality prediction of the product from the process parameters. ...
More than hundred years ago, in 1910, a first
attempt was made to polymerize butadiene to
polybutadiene. During these hundred years of this journey,
polybutadiene has almost dominated synthetic rubber
pertaining to tire industry. Apart from this, its demand as an
impact modifier, technical rubber goods and sports goods is
increasing day-by-day. Confirming the assertion, this article
focuses on hundred years journey of butadiene polymerized
synthetic rubber to current scenario. Moreover, it covers the
synthesis and characterization at bench scale to commercial
scale, reaction mechanism, role of catalyst system, solvent
system, moisture and chain transfer agent. Apart from this,
a glimpse of current trends and advances in technology is
also reviewed.
... ZNC can be based on homogeneous (including Ti, Zr and Hf complexes) and heterogeneous (including Ti complexes) catalysts. The characterisation of the heterogeneous ZNC is exceedingly challenging, compared to their homogeneous counterparts bearing a single active site, 84,85 in part owing to the presence of multiple active sites. The distribution and heterogeneity of the active sites, can then be discriminated using EPR, since as stated above, the spin Hamiltonian parameters are sensitive to changes in the local coordination environment around the metal centre. ...
... The active sites are presumed to be paramagnetic Ti 31 species featuring a metal-carbon bond, generated by the reduction of the supported Ti 41 centre by the co-catalyst. 85 The over-reduction of Ti 41 to Ti 21 and Ti 1 has also been reported. 87 Lewis bases are added to the system as additional components, not only to improve the activity of the catalyst, but also to enhance and control the stereoregularity that primarily affects the crystallinity of the polymer. ...
... ZNC can be based on homogeneous (including Ti, Zr and Hf complexes) and heterogeneous (including Ti complexes) catalysts. The characterisation of the heterogeneous ZNC is exceedingly challenging, compared to their homogeneous counterparts bearing a single active site, 84,85 in part owing to the presence of multiple active sites. The distribution and heterogeneity of the active sites, can then be discriminated using EPR, since as stated above, the spin Hamiltonian parameters are sensitive to changes in the local coordination environment around the metal centre. ...
... The active sites are presumed to be paramagnetic Ti 31 species featuring a metal-carbon bond, generated by the reduction of the supported Ti 41 centre by the co-catalyst. 85 The over-reduction of Ti 41 to Ti 21 and Ti 1 has also been reported. 87 Lewis bases are added to the system as additional components, not only to improve the activity of the catalyst, but also to enhance and control the stereoregularity that primarily affects the crystallinity of the polymer. ...
Paramagnetic (open-shell) systems, including transition metal ions, radical intermediates and defect centres, are often involved in catalytic transformations. Despite the prevalence of such species in catalysis, there are relatively few studies devoted to their characterisation, compared to their diamagnetic counterparts. Electron Paramagnetic Resonance (EPR) is an ideal technique perfectly suited to characterise such reaction centres, providing valuable insights into the molecular and supramolecular structure, the electronic structure, the dynamics and even the concentration of the paramagnetic systems under investigation. Furthermore, as EPR is such a versatile technique, samples can be measured as liquids, solids (frozen solutions and powders) and single crystals, making it ideal for studies in heterogeneous, homogeneous and enzyme catalysis. Coupled with the higher resolving power of the pulsed, higher frequency and hyperfine techniques, unsurpassed detail on the structure of these catalytic centres can be obtained. In this Chapter, we provide an overview to demonstrate how advanced EPR methods can be successfully exploited in the study of open-shell paramagnetic reaction centres in heterogeneous, homogeneous and enzymatic catalysts, including heme-based enzymes for use in biocatalysts, polymerisation based catalysts, supported microporous heterogeneous catalytic centres to homogeneous metal complexes for small molecule actions.
... ZNC can be based on homogeneous (including Ti, Zr and Hf complexes) and heterogeneous (including Ti complexes) catalysts. The characterisation of the heterogeneous ZNC is exceedingly challenging, compared to their homogeneous counterparts bearing a single active site, 84,85 in part owing to the presence of multiple active sites. The distribution and heterogeneity of the active sites, can then be discriminated using EPR, since as stated above, the spin Hamiltonian parameters are sensitive to changes in the local coordination environment around the metal centre. ...
... The active sites are presumed to be paramagnetic Ti 31 species featuring a metal-carbon bond, generated by the reduction of the supported Ti 41 centre by the co-catalyst. 85 The over-reduction of Ti 41 to Ti 21 and Ti 1 has also been reported. 87 Lewis bases are added to the system as additional components, not only to improve the activity of the catalyst, but also to enhance and control the stereoregularity that primarily affects the crystallinity of the polymer. ...
... ZNC can be based on homogeneous (including Ti, Zr and Hf complexes) and heterogeneous (including Ti complexes) catalysts. The characterisation of the heterogeneous ZNC is exceedingly challenging, compared to their homogeneous counterparts bearing a single active site, 84,85 in part owing to the presence of multiple active sites. The distribution and heterogeneity of the active sites, can then be discriminated using EPR, since as stated above, the spin Hamiltonian parameters are sensitive to changes in the local coordination environment around the metal centre. ...
... The active sites are presumed to be paramagnetic Ti 31 species featuring a metal-carbon bond, generated by the reduction of the supported Ti 41 centre by the co-catalyst. 85 The over-reduction of Ti 41 to Ti 21 and Ti 1 has also been reported. 87 Lewis bases are added to the system as additional components, not only to improve the activity of the catalyst, but also to enhance and control the stereoregularity that primarily affects the crystallinity of the polymer. ...
... The kinetic rate constants for each reaction rate is dened as a function of temperature as Arrhenius' law, with frequency factors and activation energy in terms of a one-site kinetic model, as presented in Table 1. [26][27][28] The propagation and deactivation steps are essential steps to dene activity of catalysts and productivity. Previously, Zacca and coworkers 27 have used a one-site model in good agreement with the experimental data of Drusco and Rinaldi. ...
... The rate constants for this polymerization at 69 C are obtained from literatures, 27,28 and the activation energy is obtained from Boor. 26 The frequency factor and activation energy for this polymerization are shown in Table 1. The reaction rate expressions can be written as shown in eqn (7)- (13) in Table 2.where [C M ] is the concentration of monomer (kmol m À3 ), [C s,C* ] the molar concentration of active catalyst (kmol m À3 ), ½C P * i the molar concentration of active polymer of length i (kmol m À3 ), [C H 2 ]the concentration of hydrogen (kmol m À3 ), i the degree of polymerization, ½C P * 1 the molar concentration of active polymer of length 1 or active monomer (kmol m À3 ), and [C P i ] the molar concentration of dead polymer of length i (kmol m À3 ). ...
The effects of operating conditions and scaling-up on reactor temperature control and performance in propylene polymerization fluidized bed reactors were studied by phenomenological and CFD models. A phenomenological model with CFD hydrodynamics parameters predicts average information, while a CFD-based reactor model provides local information. Results suggest improved productivity and reactor temperature control by cautiously increasing catalyst feed rate, operating temperature, reactor size and superficial velocity, with consideration of hot spots and catalyst deactivation. High catalyst loading increases productivity but involves risk with regards to the control of oscillating temperature and hot spots. The model identifies an operating window to improve productivity and temperature control and to study operation details. Mixing effect is important to heat transfer but not to propylene conversion. Scaling-up cannot provide similarity of heat transfer. Keeping the same temperature when scaling up from 0.2 to 4 m in diameter requires heat transfer area multiplying factors of 2.43 to 5.26 or lowering the wall temperature by 7 to 18 K. Hot spots are detected with a temperature variation of 10 to 14 K. The results are useful for analyses of laboratory and industrial scale reactors and provide information on scale up.
... According to the definition proposed by Boor, a Ziegler-Natta catalyst is a combination of a transition metal compound and a main group metal-alkyl compound (11). Later studies proved that the main group metal-alkyl compound acts as a cocatalyst to assist in the formation of the catalytic active species comprising the transition metal. ...
... At low Al/Ti ratios, this reaction yields titanium trichloride as a solid precipitate. TiCl 3 exists in four crystalline modifications, the , , , and forms, of which the -modification has a linear (chain-like) structure and the , , and forms have a layered structure (11,12). The reaction product of TiCl 4 and AlR 3 is -TiCl 3 , which can be converted to the form by heating. ...
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.
... The mechanism of this reaction includes the connection of hydroxyl groups' oxygen on the surface of alumina supporter to metal in the complex. [59][60][61][62][63][64] The possible mechanism of the adsorption of Co(acac) 2 catalyst on the surface of alumina support is shown in Scheme 2. As shown in this scheme, there is a possibility of connectivity of oxygen atom in two types of hydroxyl on the surface of alumina to cobalt and also coordination of Co(acac) 2 complex. In the adsorption process, bonding of AlAOACo leads to thermodynamically an endothermic reaction, but it has been suggested that the reaction due to higher stability of Co(acac) 2 complex (lower energy level) by bonding at ambient temperature (298 K) or higher temperatures, occurs spontaneously (DG < 0). ...
... As mentioned in section "Adsorption Mechanism," alumina particles with various hydroxyl groups on their surface act as an electron donor ligand and a Lewis base is capable of coordinating with the catalyst complex. 31,59,60 The probable mechanism of progress in CMRP reaction using either unsupported Co(acac) 2 catalyst (absence of alumina) or [alumina-Co(acac) 2 ] catalyst (presence of alumina) is shown in Scheme 3. ...
An alumina support system for cobalt(II) acetylacetonate (Co(acac)2) catalyst was studied for the cobalt‐mediated radical polymerization (CMRP) of vinyl acetate (VAc). We report a simple but efficient technique to produce this supported catalysts through the adsorption of Co(acac)2 on the surface of alumina particles. Moreover, kinetic and thermodynamic study of Co(acac)2 adsorption on the alumina support were conducted and the influence of effective parameters were investigated. It was found that using alumina‐supported Co(acac)2 for radical polymerization of VAc yields polymers with controlled molecular weight, narrow molecular weight distribution, and high purity. For the alumina‐supported CMRP, changing the polymerization mechanism and domination of termination pathway compared to degenerate transfer pathway resulted in a 2.5 times increase in polymerization rate (kap) and a drop in induction time while maintaining a good control of the VAc polymerization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46057.
... 为了解释在 α,ω-双烯烃的均聚过程中主链上脂肪 环的产生, Boor [6] 提出了"一步加成"的机理, 在这种机 理中, 1,5-己二烯的两个双键均与金属中心发生配位, 随后金属与两个双键发生插入反应得到甲基环戊烷结 构单元(图 4). 随着时间的推移, 这种机理越来越难解释 聚合过程中的一个核心问题, 那就是催化剂是如何控制 环本身的顺反构型的, 按照 Boor 的 "一步加成" 机理, 双 烯体上的两个双键同时配位到金属中心上, 得到的聚合 物环应当全为顺式构型, 但实验结果证明聚合物顺式或 反式环的比例是可以被催化剂本身的结构所控制的. 因 此, Marvel 和 Garrison [7] 随后提出的 "两步加成" 过程(图 5)越来越受到大家的认可. ...
... 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.
... For ID/Mg mol ratio from 0.15 to 0.25, the activity of the catalyst decreased with increase in the DIBP amount. This can be explained by the fact that excess of internal donor prevents TiCl4 coordination on MgCl2 crystal faces by occupying some of the active sites on MgCl2 support and hence decreases the activity of catalyst [40]. Therefore, the ratio of 0.15 for ID/Mg resulted in catalyst (ZN#635) has high activity with regular morphology of the polymer. ...
... [25] Regarding cyclic olefin metathesis, six-membered rings do not undergo ROMP due to their low strain energy. [26][27][28][29][30][31] Both reactions cyclo-octane metathesis and cyclo-octene metathesis have in common that reducing the ring size of the substrate is affecting the reaction rate. For cyclic alkane metathesis it is due to the large MÀ CÀ CÀ H angle of the beta-H elimination step, too high to allow beta-H elimination. ...
Metallo‐carbynes grafted on mesoporous fibrous silica are active towards alkane metathesis. We are comparing the activity of well‐defined grafted pre‐catalysts (≡Si−O−)W(≡CCMe3)(i−CH2CMe3)2, (≡Sii−Oi−)W(≡CH)(i−CH3)2 and (≡Sii−Oi−)Mo(≡CCMe3)(i−CH2CMe3)2 for Ring Opening Metathesis Polymerization of cyclo‐octene and metathesis of cyclo‐octane. This comparison is because olefins are assumed to be intermediate products in alkane metathesis. The three pre‐catalysts are active in cyclo‐octane metathesis, and give the higher, and lower cyclic homologues. However, with cyclo‐octene the three catalysts give polyoctenamer by classical ROMP. It is assumed that the metallo‐carbynes react differently towards cyclo‐alkanes and cyclo‐olefins. In one case, with cyclo‐alkanes they give a metallo‐carbene alkyl and in the other case with cyclo‐olefins they give a bis‐carbene.
... In 1930, it was developed and industrially produced on a large-scale by the BASF Company in Germany and Dow in USA. 1 Aer a few years, and because of the achievements made using Ziegler-Natta catalysts in the eld of polymer synthesis, both isotactic and syndiotactic polystyrene were also successfully prepared and then aer characterization were found to be semi-crystalline materials. [2][3][4][5] Thus, PS has become one of the most promising thermoplastics in a variety of engineering applications because of its excellent properties compared with other petroleum-based plastics. ...
Natural fibre-polymer adhesion can be improved by treating the fibre surface or polymer. In this study, resorcinol-hexamethylenetetramine mixture (R-HMT) is used as a chemical treatment for kenaf fibre waste to extend the interfacial adhesion between the fibre-polystyrene matrices. The effect of the untreated and treated kenaf fibre (designated as UK and TK fibre) on the thermal (DSC), viscoelastic, mechanical, hydrophobicity, and barrier properties of polystyrene (PS) was studied. Four different percentages of each type of fibre (10, 20, 30, and 40 wt%) were used. The chemical structure of the TK fibre was confirmed by Fourier-transform infrared spectroscopy (FT-IR) analysis. The compatibility of the fibre-polymer was investigated by scanning electron microscopy (SEM). The results showed that the use of the treated fibre at 30 wt%, enhanced the tensile strength by 148% and 212% compared to neat PS and PS/UK-30, respectively, indicating a good fibre bond adhesion. The DMA data demonstrated that the storage modulus increased significantly, especially for the PS/TK-30 composite. Meanwhile, the glass transition temperature (Tg) shifted to a lower temperature for both types of fibre. Also, the hydrophobicity of the PS composites, which was determined by thickness swelling measurements, was improved when the TK fibre was inserted. Furthermore, water vapor and oxygen transmission rates were determined. A good correlation between most of the properties for the PS composite-based treated fibre was observed, which revealed the possibility of using these materials for sustainable automotive components and gas sensitive packaging applications.
... The particle morphology of polyolefins has been generally influenced by the morphologies of catalyst particles, polymerization condition and the effect of molecular organization such as polymer crystallization [4,7]. In olefin polymerization, the catalyst particle morphology such as shape, pore and particle size distribution [8][9][10][11][12][13] has an important impact on the rate of mass transport of reactants and the diffusion of diluents inside the growing particle, and thus it affects the rate of polymerization and molecular architecture of final polymer including chain length distribution, comonomer content and so on [14,15]. In addition, polymerization conditions, especially in the initial stages of polymerization, also play a key role in controlling the particle morphology. ...
The effects of particle morphology on the structure and swelling/dissolution and rheological properties of nascent ultra-high molecular weight polyethylene (UHMWPE) in liquid paraffin (LP) were elaborately explored in this article. Nascent UHMWPE with different particle morphologies was prepared via pre-polymerization technique and direct polymerization. The melting temperature and crystallinity of UHMWPE resins with different particle morphologies were compared, and a schematic diagram was proposed to illustrate the mechanism of UHMWPE particle growth synthesized by pre-polymerization method and direct polymerization. The polymer globules in the nascent UHMWPE prepared by using pre-polymerization technique are densely packed and a positive correlation between the particle size and the viscosity-averaged molecular weight can be observed. The split phenomenon of particles and the fluctuation in the viscosity of UHMWPE/LP system prepared by direct polymerization can be observed at a low heating rate and there is no correlation between particle size and viscosity-averaged molecular weight.
... Countless are the examples in which chemists have left their marks on the history of technical and technological evolution. Since the manipulation of radioactive elements by the Curie couple (Curie, 1903) till the development of rubber formulations by Goodyear (Korman, 2002) -which would later be used for tire manufacturing -through the development of catalysts used in polymerization by professors Ziegler and Natta (Boor, 1979), Chemistry has always been present. And, in all those examples, it has left its mark: that of a Science capable of transforming the world. ...
As consumption and use increased, the accumulation of urban waste of polymeric origin drew the attention of several sectors, especially that of the organized civil society. Through mobilizations and activism, environmental became more restricted regarding the use and disposal of polymer materials. Plastic bags, tires, disposable cups, plastic straws, PET bottles are some examples of how polymers have had a negative impact to the environment generating pressures around the world to rethink their uses. However, the pandemic crisis that emerged in January, 2020 has reinforced the importance of polymers for contemporary society. If, in the past, consumerism was the driving force behind the application of polymers, nowadays health and medical emergencies are the new forces. The reduction in stocks of medical-hospital supplies and personal protective equipment for health professionals and for the general public caused by the pandemic led to the emergence of alternative production movements based on polymers. Because of those alternatives, which have helped a lot to save and preserve lives, the present work aims to highlight the types of polymers most used during this pandemic period. For this purpose, scientific articles related to the production of masks and other devices having some type of polymer as raw material were analyzed. The present research was based on the first half of 2020, highlighting the countries, the polymer used, and the final product it is intended to.
... 会发生向分子链内的β-H转移而自身终止. 水、醇、 酸、胺等含活性氢的化合物是配位聚合常用的终止 剂 [77] . ...
... [20,21] Whilst the reactivity of Group 14 [22] and boron multiple bonds [23] is rather well-established, aluminum multiple-bond chemistry is still in its infancy. [24] Even though aluminum is the most abundant metal found within the Earthscrust, and the high industrial use of Al III related catalysts, [25,26] research into low oxidation state and/or low coordinate Al I complexes is somewhat often overlooked owing to the synthetic challenges in isolating such reactive species.D espite this,r ecent advances in Al I chemistry have shown that not only can Al react as an electrophile and undergo oxidative addition reactions [27] but also as an ucleophile and thus challenging traditional conceptions of the chemical behavior of aluminum. [28,29] Recently our group succeeded in isolating the first neutral dialumene (1)s pecies,acompound with af ormal Al = Al double bond. ...
CO2 fixation and reduction to value‐added products is of utmost importance in the battle against rising CO2 levels in the Earth's atmosphere. An organoaluminum complex containing a formal aluminum double bond (dialumene), and thus an alkene equivalent, was used for the fixation and reduction of CO2. The CO2 fixation complex undergoes further reactivity in either the absence or presence of additional CO2, resulting in the first dialuminum carbonyl and carbonate complexes, respectively. Dialumene (1) can also be used in the catalytic reduction of CO2, providing selective formation of a formic acid equivalent via the dialuminum carbonate complex rather than a conventional aluminum–hydride‐based cycle. Not only are the CO2 reduction products of interest for C1 added value products, but the organoaluminum complexes isolated represent a significant step forward in the isolation of reactive intermediates proposed in many industrially relevant catalytic processes.
... Aluminum alkyls, including trialkylaluminum and alkylaluminum chlorides, are important components in classical heterogeneous Ziegler-Natta coordination polymerization catalysis. 64 olefins. 66,67 Although as the temperature of the polymerization increases, the polymerization becomes nonstereospecific in these systems, they can be used to prepare a variety of homo, block, random, and alternating polyolefins. ...
New methods for the preparations of oxygen-bridged heterobi and heterotrimetallic
complexes of early transition metals and main group metals which are difficult to achieve by
other methods, have been developed during the present work.
... The history of polyolefin polymerization catalysts commenced with Ziegler and Natta's discovery of heterogeneous catalysts [6][7][8], which have been found to be a workhorse of the polymer industries. Despite the many advantages of these catalysts, the uncertainty as to the nature of the multi-active sites has hindered better understanding of their polymerization mechanism. ...
The physical properties and end applications of polyolefin materials are defined by their chain architectures and topologies. These properties can, in part, be controlled by a judicious choice of the steric and electronic properties of the catalyst and, in particular, the ligand framework. One major achievement in this field is the discovery of thermoplastic polyolefin elastomers that combine the processing and recyclable characteristics of thermoplastics with the flexibility and ductility of elastomers. These polymers are highly sought after as alternative materials to thermoset elastomers. In this perspective, works in the literature related to the development of nickel catalysts as well as their implementations for the synthesis of polyolefin elastomers are summarized in detail. Throughout the perspective, attention has been focused on developing the relationship between catalyst structure and performance, on strategies for the synthesis of polyolefin elastomer using nickel catalysts, on properties of the resultant polyolefin, such as degree of branching and crystallinity, as well as on their effects on mechanical properties. The future perspective regarding the most recent developments in single-step production of polyethylene elastomers will also be presented.
... OCP VMs are primarily made of ethylene and propylene monomer units and are synthesized via Ziegler-Natta vanadium-based [31] or metallocene catalysis [32,33]. Variations in OCP chemistry are also commercially available, i.e., ethylene-propylene-diene monomer (EPDM) that include additional diene monomers. ...
This article reviews viscosity modifiers, additives that increase the viscosity of lubricating oils. Viscosity modifiers are high molecular weight polymers whose functionality is derived from their thickening efficiency, viscosity–temperature relationship, and shear stability. There are now many different additive chemistries and architectures available, all of which have advantages and disadvantages, and affect solution viscosity through different mechanisms. Understanding these mechanisms and how they impart additive function is critical to the development of new viscosity modifiers that enable lubricants to function more efficiently over a wide range of temperatures.
... Cation-π interactions involving transition metals are important throughout organometallic chemistry [1][2][3][4][5], and they play critical roles in catalytic processes [6][7][8] and supramolecular interactions in biology [9,10]. Transition metalolefin complexes are present as key intermediates in several chemical processes of industrial significance. ...
Au(C2H2)n⁺ (n = 1–6) ion–molecule complexes are produced in the gas phase via pulsed laser vaporization in a supersonic expansion of acetylene and argon. Cations are size selected and studied with infrared photodissociation spectroscopy in the C–H stretching region (3000–3500 cm⁻¹). Insight into the structure and bonding of these species is obtained from the number of infrared active bands, their relative intensities and their frequency positions. Density functional theory calculations provide structures for these complexes and predicted spectra are compared to the experiment. The combined data indicate that gold cation has a primary coordination number of two with respect to acetylene binding, and a secondary coordination sphere that is completed with a third ligand. Larger complexes (n = 4–6) are formed by solvation of the Au(C2H2)3⁺ core ion with acetylene, in a pattern like that seen previously for Cu(C2H2)n⁺ complexes. Small differences in the spectra between corresponding copper and gold cation complexes are explained by theory, but only when relativistic corrections are included for the gold complexes.
... When the ethylene-propylene ratio is decreased resulting in an amorphous OCP, thickening is reduced to some extent and low-temperature properties are improved [56][57][58]. OCPs are generally manufactured by solution Ziegler-Natta polymerization [59]. Metallocene polymerization is also used where a higher level of control over stereoregularity, molecular weight distribution, and composition is required [60][61][62]. ...
In this contribution, we report the synthesis of two naphthoxy imine ligands, 2-(((2,6-dibenzhydryl-4-methoxyphenyl)imino) methyl) naphthalen-1-ol (L1), and 2-(((2,6-diisopropylphenyl)imino) methyl) naphthalen-1-ol (L2) with different steric and electronic features. L1 and L2...
The authors have assessed the possibility of electrochemical synthesis of a wide range of reagents based on titanium trichloride as part of the work. Despite the growing demand for titanium trichloride and its derivatives, the production technology of this reagent has not been improved for a long period. Traditional technologies feature high environmental and industrial hazards, and the process itself has high energy consumption and a complex hardware scheme. As part of preliminary work, the possibility of obtaining titanium trichloride from aqueous solutions of titanium tetrachloride is established, while the proposed technology is distinguished by reduced energy consumption and safety. At the first stage of experiments in the anodic dissolution of aluminum, binary solutions of titanium trichloride and aluminum chloride are obtained. The degree of conversion TiCl4 → -TiCl3 is 65%–35% for a current density of 10–30 A/dm2, respectively. In the process of reducing an aqueous solution of titanium tetrachloride with iron electrodes, the yield of titanium trichloride is approximately 76%–66% for a current density of 10–30 A/dm2, respectively. The resulting solution is heavily contaminated with iron (II) compounds. The results of the experiments show the high efficiency of this solution in the processes of purification of wastewater from galvanic production from chromium (VI) compounds. For the production of high-purity titanium trichloride, titanium electrodes are used, while the yield of titanium trichloride is 59%–3% for a current density of 10–30 A/dm2, respectively. Depending on the production technology and electrode material, solutions are obtained that can be used to produce high-purity titanium dioxide for the production of dye-sensitized solar cells, reagents for water purification, and a Ziegler-Natta catalyst and a reagent for organic synthesis.
This paper considered the performance of water condenser and coolers in the bulk section of polypropylene plants using the Spheripol Process. The condenser and coolers were installed to capture condensable from recycle steams. The efficiency of polypropylene condenser was least in all the coolers and condenser under the scope of this study. A model was developed to demonstrate how the catalyst activity or mileage could be enhanced. A computer simulation was carried out and the result obtained shows the effects of reactor density and residence time on catalyst mileage.
Establishing a relationship between structural characteristics of a catalyst system and morphology of polymer particles, on the one hand, and the kinetic characteristics of the catalysts in relation to the molecular weight of the resulting polymer on the other hand, is an important scientific task and has considerable applications. In this paper, for the first time, data on the formation of polyethylene particles with different molecular weights and different morphologies on two samples of highly active supported titanium–magnesium catalysts (TMC) having different textural characteristics (pore structure and crystallite size) are obtained. It is shown that this effect persists with varying polymerization conditions (polymerization temperature, the presence and absence of hydrogen as a polymer chain transfer agent) and titanium content in the catalyst. The discussion of possible causes of the revealed differences in molecular weight of the produced polymers is based on the kinetic data and morphological analysis of the polymer particles formed on TMCs with different structural characteristics and titanium contents. The formation of PE with different molecular weights over these catalysts may be related to different concentrations of ethylene in the subsurface layer of polymer near active sites of the catalysts.Graphical abstract
The transition metal catalysts have evolved dynamically in last few years for propylene polymerization and copolymerization in homogeneous media. The trends in catalyst development have moved from modification of Group...
Slurry polymerization processes using Zeigler–Natta catalysts, are most widely used for the production of polyethylene due to their several advantages over other processes. Significant advancements have been made in the modeling of these processes to obtain high-quality final products. The modeling work in this field has a very wide scope due to the great diversity of the catalyst types, polymerization processes, polymerization conditions, product qualities and microstructures that exist at the commercial scale. In this article, we have reviewed and discussed the slurry polymerization processes for the production of polyethylene and the multiscale modeling and simulation framework in slurry reactors. The multiscale modeling framework mainly comprises of the kinetic model, single-particle diffusion models, multiphase hydrodynamics, phase equilibria, reactor residence time distribution and the overall mass and heat balances. Guidelines to implement the multiscale mathematical modeling and simulation in slurry-phase olefin polymerization processes are proposed. Special focus is given on the need to reduce the computational effort for the simulation of industrial reactors so that the models can be used as an effective tool-kit for optimization studies using state-of-art algorithms.
This Editorial discusses two seminal Macromolecules publications by Ishihara et al. concerning the synthesis of syndiotactic polystyrene. In a 1986 communication (Macromolecules1986, 19, 2464), the first preparation of this semicrystalline polymer was reported. A 1988 full paper (Macromolecules1988, 21, 3356) described the enabling polymerization catalyst system, based on methylaluminoxane-activated half-metallocene titanium complexes. These two highly cited publications inspired a large body of research concerning the synthesis, structure, properties, and applications of this new polymer.
When Ziegler–Natta catalysts synthesize “random” copolymers, they give multiblocks copolymers. Chains of butene–ethylene copolymers contain blocks with long and short butene sequences that crystallize in forms II and I of iPB, respectively.
CO2 fixation and reduction to value added products is of utmost importance in the battle against rising CO2 levels in the Earth’s atmosphere. Herein we present the use of an organoaluminium complex containing a formal aluminium double bond (dialumene), and thus an alkene equivalent, for the fixation and reduction of CO2. The CO2 fixation complex undergoes further reactivity in either the absence or presence of additional CO2, resulting in the first dialuminium carbonyl and carbonate complexes, respectively. Dialumene (1) can also be used in the catalytic reduction of CO2, providing selective formation of a formic acid equivalent via the dialuminium carbonate complex rather than a conventiona aluminium‐hydride based cycle. Not only are the CO2 reduction products of interest for C1 added value products, but the novel organoaluminium complexes isolated represent a significant step forward in the isolation of reactive intermediates proposed in many industrially relevant catalytic processes.
The paper considers a convolution model for polymerization of 1,3-dienes in the presence of organometallic catalysts. It is shown that initial steps of polymerization can be represented as a set of shifted parallel reactions of the chain propagation, in which shift value are governed by the kinetics of the initiation step. In this case, polymer accumulation curve is described by an equation containing convolution of functions which allow one to solve an inverse problem of restoring the function of active site accumulation. Based on the example of isoprene polymerization over neodymium catalyst, it was demonstrated that the results of the inverse problem solution are in good agreement with the experimental data on concentration of the active sites. These data were obtained by a method of controlled introduction of inhibitor in short-time polymerization.
Accurately measuring molecular kinetics of catalytic olefin polymerization has been a challenging objective. Many methods have been proposed in the literature but all of them have drawback(s). In this paper, we introduce a labeling method to count active sites employing methyl propargyl ether (MPE) as the quench-labeling agent. It is commercially available, does not react with Al-alkyl species and has a labeling efficiency close to 100%. The labeling reaction was evidenced by a mechanistic study on the reaction between the model system Cp2ZrMe2/MAO (Cp = cyclopentadienyl) and MPE that it may occur through a coordination-insertion mechanism without noticeable multiple insertions. The method was benchmarked by studying a MgCl2-supported Ziegler-Natta catalyst in 1-hexene polymerization. The fraction of the active transition metal χ* is found to be <1%. It rises in the very first few seconds and reaches a plateau within 10 s in the absence of precontact. With precontact χ* remains constant over polymer yield from 0.3 up to 5.3 g(PH) g(cat)⁻¹, demonstrating that χ* does not necessarily grow during polymerization. Longer precontact resulted in decreased χ* and decreased average rate constant of propagation which is in the order of 10² M⁻¹s⁻¹.
A silicon-aluminum heterocycle LAl(SiH2SiH2)2AlL (L = PhC(NtBu)2) (1) was prepared. Compound 1 exhibits a unique (N2Al)2(SiH2)4 centrosymmetric six-membered ring structure with chair conformation, which is comparable with that of cyclohexane. Furthermore, two intermediate analogues, silylene-alane adduct LSi(AlMe3)-Si(AlMe3)L (2) and silylene-alane oxidative product [LAlHSiH2Mes]2 (3) were obtained. Compound 3 has an interesting arrangement of an Al-H and a SiH2 unit, which are in close neighborhood to each other. 3 might be important to function as a catalyst, due to the already activated bridging Al-H bonds
Over the last 60 years the ability to reduce olefinic refinery gases or liquids into a metastable solid in a controlled manner has created the colossal business of polyolefin materials. Their continued success is thanks to a deep understanding of how to meet and predict a customer’s needs in terms of a price/performance package and translate that back through the chain of knowledge (Fig. 1.1). This demand has led to constant evolutions within all areas of the business, punctuated by more than its fair share of revolutionary breakthroughs in the areas of catalyst, polymerization process, and polymer processing technology.
This chapter aims to discuss some important technical aspects of the commercial support related to each catalyst technology toward the production of different polyolefin grades. It approaches several industrial factors that are defined by the fine tuning between support and catalyst preparation, such as the catalyst fragmentation, the control of the final particle morphology and the morphological replication phenomena, the heat and mass transfer limitations during the polymerization reaction, and the uses of prepolymerization stage. The understanding of these parameters and the limits of the polymerization processes are the first step for designing a suitable support for a heterogeneous catalyst. Aspects such as chemical composition of the support, its surface characteristics, morphology (surface area, particle size, particle size distribution, and porosity), mechanical strength, and other characteristics of relevance for the two most common supports in the polyolefin industry—MgCl2 and SiO2—are discussed as well.
Two MgCl2-supported Ziegler-Natta model catalysts were prepared by contacting activated MgCl2 with deficient or excess amount of TiCl4. Ethylene/1-hexene copolymerization with the catalysts was conducted under different 1-hexene feed, and active center concentration of the reaction system was determined by quench-labeling method using thiophene-2-carbonyl chloride as the quencher. The catalytic activity was only moderately enhanced (increment <50%) by adding 1-hexene in ethylene polymerization with the model catalyst (Cat-1) of 0.1 wt% Ti content, and the active center ratio ([C*]/[Ti]) was only slightly increased (from 64 to 72 mol%). The comonomer activation effect in Cat-1 catalyzed copolymerization was mainly attributed to increase of apparent propagation rate constant by the comonomer, which can be explained by reduction of mass transfer barrier in the polymer/catalyst particles because of larger monomer diffusion coefficients in the copolymer phase than in the more crystalline polyethylene phase. In contrast, the activity was nearly tripled by adding 1-hexene when the catalyst of 1.47% Ti content (Cat-2) was used, meanwhile its [C*]/[Ti] was also tripled (from 15 to 49 mol%). The strong comonomer activation effect in Cat-2 catalyzed copolymerization was caused by marked increase of active center concentration. In this case, fragmentation of the polymer/catalyst particles was intensified by adding the comonomer, and more active centers that were originally inaccessible to the cocatalyst and monomer were exposed through the particle fragmentation. According to the results of this work, the comonomer effect in conventional supported Ziegler-Natta catalysts can be explained by the combination of physical factor (increase in diffusion coefficient) and chemical factor (exposure of inaccessible active center precursors through particle fragmentation).
This chapter is devoted to the observation of general methods of polymer synthesis including radical, ionic, coordination, and metathesis polymerization. The main advantages, possibilities, and drawbacks of each method are discussed. A special emphasis was placed to the modern methods of controlled polymer synthesis leading to well-defined polymers with desired structure, composition and properties. Such methods are considered as a way to the novel polymer materials for various high-tech applications.
Synthesis and isolation of stable main group compounds featuring multiple bonds has been of keen interest for the last several decades. Multiply bonded complexes were obtained using sterically demanding substituents that provide kinetic and thermodynamic stability. Many of these compounds have unusual structural and electronic properties that challenges the classical concept of covalent multiple bonding. In contrast, analogous aluminium compounds are scarce in spite of its high natural abundance. The parent dialumene (Al2H2) has been calculated to be extremely weak, thus making Al multiple bonds a challenging synthetic target. This review provides an overview of these recent advances in the cutting edge synthetic approaches used to obtain aluminium homo‐ and heterodiatomic multiply bonded complexes. Additionally, the reactivity of these novel compounds towards various small molecules and reagents will be discussed herein. This review provides an overview on the current progress in aluminium multiple bond chemistry and the careful ligand design required to stabilise these reactive species.
The stereospecificity for α‐olefin polymerization catalyst is governed by the catalysts’ ability to discriminate between the two faces of the prochiral α‐olefin molecule for a given mode of insertion. This chapter concentrates on the ability to control the polymer properties with heterogeneous stereospecific catalysts, focusing on polypropylene (PP) catalysts in particular. Heterogeneous PP catalysts typically operate in particle forming processes, such as slurry, bulk, or gas‐phase polymerization technologies. The demonstration of stereoregular polymerization of an α‐olefin led to a rapid growth in new polymers and industrial applications as the potential of Ziegler–Natta catalysts was realized. The mechanism of polymerization for the catalyst system was controlled by the ligand and was termed site control. Over the past three decades, there have been a large number of industrial and academic publications in the field of single site polyolefin polymerizations.
The polymer particles in both morphology‐controlled and irregular forms were reported using similar method of preparing morphology‐controlled catalysts and similar polymerization procedures. This chapter describes procedures for the reproducible operations of the slurry and gas‐phase polymerization reactors. It discusses the prepolymerization and polymerization results with emphasis on the dependence of the prepolymerization/polymerization activity profiles and prepolymer/polymer properties on the particle sizes. Effects of catalyst and polymer particle sizes on activity profiles and polymer properties have frequently been examined only in the modeling studies of mass and heat transfer limitations in heterogeneous olefin polymerization, but not very often in experimental studies. Very little information on the preparation technique can be found on these morphology‐controlled MgCl2/TiCl4 catalysts; and the chapter explains detailed procedures for these two types of catalysts prepared in the laboratory. Mass and heat transfer limitations are unlikely in gas‐phase polymerization reactors with prepolymerized catalysts.
The preparative-temperature rising elution fractionation method is used to obtain comparative data on contents of fractions with different microtacticities for polypropylene (PP) samples prepared using three catalytic systems: the traditional Ziegler–Natta (Z–N) catalyst δ-TiCl3 and two types of supported titanium–magnesium catalysts: the “donor-free” TiCl4/MgCl2 catalyst and TiCl4/MgCl2·nDBP catalyst (DBP – dibutylphthalate used as an internal donor) at polymerization with the same cocatalyst (AlEt3) in the absence and presence of an external donor (propyltrimetoxy silane). The separated individual PP fractions are also studied by gel permeation chromatography (molecular weight and molecular weight distribution) and differential scanning calorimetry. The results demonstrate general regularities and differences in the formation of active sites having different isospecificities for the traditional TiCl3-based Z–N catalyst and highly active supported titanium–magnesium catalysts.
Cobalt-mediated radical polymerization (CMRP) of vinyl acetate (VAc) has been suggested as one of the major methods to reduced some of the problems in the synthesis of Poly(vinyl acetate) (PVAc), but the color impurities have been the major disadvantage of this method. An easy and practical method to make a crystallized PVAc in a one step process is to use silica gel particles. The particles have been used as a catalyst support of cobalt(II) acetylacetonate (Co(acac)2). It was found that using silica gel supported-Co(acac)2 in VAc polymerization yields polymers with controlled molecular weight, narrow molecular weight distribution, and high purity. For the silica gel supported CMRP (SS-CMRP) changing the polymerization mechanism resulted in a 2.5 times increase in polymerization rate (kapp) and a drop in the induction time while maintaining the control of the VAc polymerization. In addition PVAc synthesized through SS-CMRP method compared to the one synthesized using unsupported-CMRP has a higher crystallinity. Graphical abstract ᅟ ᅟ
The polymerization of ethylene with Ziegler-Natta catalysts in the presence of carbon black has shown three characteristic features both with a heterogeneous catalyst, AlBu3TiCl4, and with a soluble catalyst, Cl2Ti(C5H5)2AlEt2Cl. They are, in order of increasing importance: reactivity of the organoaluminum derivatives with surface chemical groups of the carbon black, adsorption of a certain amount of organoaluminum compounds on the carbon black surface, and influence of the specific surface of carbon black, which controls the dispersion degree of the catalytic system. Furthermore, it was possible to obtain polyethylene by this procedure, containing different amounts and different types of carbon black.
Electron donors, especially trialkylamines and azulene, have been examined in aluminum alkyl-, CH3TiCl3- and hydrogen-activated TiCl3 catalysts for the polymerization of propylene to isotactic polymer. A comparison and an evaluation were made with findings which were established earlier with zinc alkyl-based TiCl3 catalysts. We find that the donor, when it is present in low concentrations in all of the above catalysts, can inactivate preferentially the less stereoregulating sites. In this way the isotactic content and the molecular weight of the polymer are increased, but only at the expense of a lower catalyst activity. The addition of hydrogen to the TiCl3–donor catalyst at −78°C produced a threefold effect: (1) the activity of the catalyst was increased about 5 to 15 times and higher, (2) the polypropylene formed with this more active catalyst was more isotactic (ca. 10–15%), and (3) the polymer had a lower molecular weight. It is proposed that the increase in catalyst activity was due to the generation of Ti-H bonds to which propylene molecules then added, the Ti-H bonds thus being transformed into active Ti-C centers.
Sodium sulfate increases the polymerization activity of the titanium(III) chloride (AA)–ethylaluminum sesquichloride system for the polymerization of propylene. The reaction of ethylaluminum sesquichloride with sodium sulfate at mild conditions isolates diethylaluminum chloride, which is responsible for the polymerization activity. The reaction of these components at severe conditions forms an organometallic compound containing sulfate, (C2H5)4Al2SO4, and this compound is a powerful activator for titanium(III) chloride.
The chemistry of the titanium(III) chloride(AA)–ethylaluminum dichloride–tetrakis-(dimethylamino)silane system for the polymerization of propylene was studied. A complex of ethylaluminum dichloride with tetrakis(dimethylamino)silane was isolated. It was shown that this complex contains ethylaluminum dichloride and tetrakis(dimethylamino)silane in the ratio of 2:1. This complex with titanium(III) chloride is responsible for the polymerization activity.
Aus Mischungen von Titantetrachlorid und Alkylaluminium-Verbindungen lassen sich Organotitanhalogenide RTiCl3 und R2TiCl2 isolieren. Die reinen aluminium-freien Verbindungen sind in Gegenwart ihrer Zersetzungsprodukte TiCl3 und TiCl2 wirksame Katalysatoren für die Polymerisation von α-Olefinen. - Beim Polymerisationsprozeß wird das Monomere zwischen die TiC-Bindung eingelagert, so daß Organotitan-Verbindungen mit hochmolekularem Organo-Rest entstehen. Daneben bilden sich ungesättigte Kohlenwasserstoffe durch Übertragungsreaktion mit dem Monomeren. Die reduzierten Viscositäten dieser Produkte liegen zwischen 0,4 und 1. - Die Polymerisation mit dem Katalysatorsystem RTiCl3TiCl3 tritt als wichtiger Teilprozeß bei der Verwendung von Mischkatalysatoren aus TiCl4 und Alkylaluminium-halogeniden auf.
Die Polymerisation des Butadiens mit dem Katalysatorsystem Kobalt‐Verbindung/Äthyl‐Al‐sequichlorid in Benzol als Lösungsmittel wurde untersucht. Der polymerisationsaktive Katalysator ist ein π‐Komplex des Kobalts mit dem Butadien, bei dessen Bildung eine geringe Menge bestimmt LEWIS‐Basen anwesend sein muß (Wasser, Äther, Phosphin usw.). Im Komplex hat das Kobalt die Wertigkeit +1, die durch die LEWIS‐Base stabilisiert wird.
Mit Hilfe der adiabatischen Kalorimetrie wurde die Butadienpolymerisation mit dem Katalysatorsystem Kobalt‐III‐acetylacetonat/Äthyl‐Al‐sesquichlorid kinetisch untersucht. Die Geschwindigkeitsgleichung für die Polymerisation lautet: equation image
Die Konzentration an Äthyl‐Al‐sesquichlorid geht in die Geschwindigkeitsgleichung nicht ein. Durch den Quotienten wird eine teilweise reversible Inaktivierung des Katalysators durch das Lösungsmittel Benzol und andere Zusätze rechnerisch berücksichtigt. K D ist eine Konstante, die Donatorstärke, durch welche die Tendenz des Benzols oder anderer Zusätze, einen π‐Komplex mit dem Kobalt zu bilden, zahlenmäßig ausgedrückt wird. Durch Zusatz geringer Mengen substituierter Aromaten zum Polymerisationsansatz kann aus der Abnahme der Polymerisationsgeschwindigkeit die Donator‐Stärke derselben bestimmt werden. Die gefundenen Werte stimmen gut mit Literaturwerten überein.
In die Geschwindigkeitsgleichung für die Katalysatorbildung gehen die Konzentrationen an noch nicht komplex gebundenem Kobalt und an Äthyl‐Al‐sesquichlorid ein, aber nicht die Butadien‐Konzentration. Geschwindigkeitsbestimmend ist die Reduktion des Kobalts von der Wertigkeit +2 zu +1.
Polyethylene was prepared in a homogeneous system at 120°C. Several catalytic systems were employed, all using a soluble vanadium compound. The first consisted of an alkylaluminum compound in conjunction with the vanadium compound and a “promoter.” This promoter, which is believed to act as an oxidizing agent to reactivate dead catalyst sites, was a polyhalo compound with esters of trichloroacetic acid preferred. The promoter was added continuously throughout the polymerization. Polyethylene so produced had a narrow M̄w/M̄n ratio close to the theoretical ratio of 2.0 for a single catalyst site. Up to 266 polymer chains were produced per vanadium atom. In the second system, the cocatalyst was an AlBr3(AlCl3)–(C6H5)4Sn[(C6H5)3Bi] combination. The continuous addition of a promoter such as methyl trichloroacetate was necessary, presumably to reactivate dead catalytic sites. By this procedure, yields up to 6.6 kg of polymer per millimole of vanadium and 30–60 chains per vanadium atom were achieved. The product had a narrow M̄w/M̄n ratio of 2.4 by gel-permeation chromatography (GPC). A study of the interactions of the catalyst compounds indicated that CCl3COOR does oxidize di- and trivalent vanadium.
Ethylene polymerizations with the aged AlBr3–VXn–Sn(C6H5)4 catalyst required the presence of about 0.02% oxygen in the ethylene feed. When the catalyst components were combined in the presence of ethylene, polymerization ceased in less than 1 min. with the production of about one polymer molecule per vanadium atom. The reaction was repeatedly reactivated by the addition of milligram amounts of oxygen, ultimately resulting in a higher yield of polyethylene with a molecular weight of 230,000. In the concentration range from 0.003 to 6% oxygen in the ethylene, there was a sharp maximum in the amount of polymer produced, before polymerization ceased, at about 0.05–0.1% oxygen. However, the molecular weight of the polyethylene decreased mono-tonically with increasing oxygen concentration from 230,000 at 0.003% to 12,500 at 6.1% oxygen. It was demonstrated that oxygen enters into an oxidation-reduction cycle with the vanadium species and that this reaction induces molecular termination and reactivates the vanadium center. In the absence of oxygen, the polyethylene was found to contain one phenyl and one vinyl endgroup per polymer molecule. These data are interpreted in light of a previously proposed propagation mechanism. Polymer end group analyses suggest that termination occurs by transfer of the polymer from the active vanadium center to an inactive aluminum center when oxygen is absent and by oxidation of the vanadium active site to a catalytically inactive compound when oxygen is added.
The effect of CS2 on isoprene polymerization with triisobutylaluminum-titanium tetrachloride catalysts was studied at Al/Ti ratios of optimum (0.9) and higher values. In the absence of CS2, appreciable amounts of low molecular weight oils (“extractables”) were formed at the expense of cis-1,4-polyisoprene with higher than optimum Al/Ti ratios. Small amounts of CS2 were found to prevent extractables formation and allow attainment of higher yields of cis-1,4-polyisoprene. The optimum CS2/Ti chloride molar ratio (0.1) was independent of the Al/Ti ratio of the catalyst. Polymer microstructure and dilute solution viscosity were unaffected by CS2. The results support the theory that the catalyst surfaces hold two types of active sites: p-sites, which initiate polymerization, and o-sites, which lead to oligomerization. CS2 appears to enhance polymerization by coordinating selectively at the o-sites. The predominance of oligomerization at the higher Al/Ti ratios was attributed to a destruction of p-sites by excess trialkyl-aluminum.