Propylene polymerization with δ-TiCl3/AlClEt2 and δ-TiCl3/AlEt3 catalyst systems

Summary Some parameters of propylene polymerization using -TiCl₃/AlClEt₂ and -TiCl₃/AlEt₃ catalyst systems were evaluated. The catalyst was prepared through the reduction of TiCl₄ complexed with di-n-butyl ether (DBE) (mole ratio DBE/TiCl₄=0.67) by AlClEt₂. Propylene polymerizations were carried out at different Al/Ti ratios, using AlEt₃ or AlClEt₂ as cocatalysts and different polymerization temperatures. The effects of these parameters on catalyst activity, stereo-specificity and polymer molecular weight were investigated. The results indicate that these parameters strongly affect catalyst performance.     

A comparative study of ethylene and propylene polymerization over titanium–magnesium catalysts of different composition

New data on the molecular weight characteristics of polypropylene (PP) and polyethylene (PE) were obtained from the polymerization over supported titanium–magnesium catalysts differing in their compositions (presence and absence of internal and external donors). Internal and external donors were found to affect the molecular weight of polymers in a different manner for ethylene and propylene polymerization. The introduction of the internal donor increases the molecular weight of PP and does not affect the molecular weight of PE. The effect of external donor introduced to catalytic system on the polymer molecular weight depends on catalyst composition: for a catalyst without internal donor, the introduction of the external donor increases the molecular weight of PP and does not affect that of PE. In the case of catalyst with the internal donor, the introduction of the external donor increases the molecular weight of PP and substantially decreases that of PE. The data on polymerization degree of the polymers produced under conditions when chain transfer with hydrogen was the dominant reaction were used to calculate the values for ethylene polymerization over the catalysts of different composition. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40658.     

The influence of some synthesis parameters on Ziegler-Natta catalyst performance

Catalysts based on TiCl₃ modified by di-n-butyl ether (DBE) as internal base were synthesized with the aim to obtain polypropylene particles of controlled morphology. Two routes were used to synthesize the catalysts (System A and System B). In System A, DBE employed as internal base was complexed with TiCl₄ and diethylaluminum chloride (DEAC) in iso-octane solution and in System B, DBE was complexed with triethylaluminum (TEA) and TiCl₄ in toluene solution. The catalysts were evaluated in propylene polymerization and the polymer morphology was characterized by optical and scanning electron microscopies, bulk density and particle size distribution.     

Kinetics study of Ziegler-Natta catalyst based on TiCl3 modified by Lewis bases

Summary The kinetic in propylene polymerization of catalysts containing di-n-butyl ether (DBE) - Cat.A or di-n-butyl ether and ethyl benzoate (EB) - Cat. B used as internal electron-donor compounds was investigated. Comparing catalyst compositions with performances, one could conclude that the different kinetics observed were due to the different Lewis bases employed during catalyst synthesis. It seems that the electron-donors have modified the catalyst sites. It has found that added ethyl benzoate modified the structure of the active sites and increased the polymerization rate constant.     

The role of hindered Lewis bases on the catalyst performance of TiCl3 for propylene polymerization

Summary The effect of AlEt₃ modified by tributylamine (TBA), 1,4-diazabicyclo [2.2.2]octan (DO), 2,2,6,6-tetramethylpiperidine (TMPip), 2,6-dibutyl-4-methylphenol (BHT) and 2-tert-butyl-4-metoxyphenol (TBMP) on the propylene polymerization was studied using a catalyst based on TiCl₃ modified with di-n-butyl ether as internal base. The influence of these hindered Lewis bases on the isotacticity, catalyst activity, molecular weight ( n) and molecular weight distribution (MWD) was investigated. It was verified that the Lewis bases modified the percentage of mm triad whereas no significant effect on I.I. was found.     

Effects of external Lewis base on the performance of MgCl2 supported catalysts in propylene polymerization

Summary The effects of four different external Lewis bases on propylene polymerization using the MgCl₂-supported TiCl₄ catalyst were studied in the context of the variation of the chemical complexes formed between catalyst, catalyst support and internal Lewis base, and the interactions between complexes and external Lewis base, The internal Lewis base used in this study was dioctyl phthalate. With ethyl benzoate as the external donor no change in activity was observed, but the interaction between ethyl benzoate and MgCl₂·phthaloyl chloride complex resulted in a decrease of isotacticity. Increasing the bulkiness of the external Lewis base hindered the monomer coordination. It was found that the relative amount of the phthaloyl chloride complex to other complexes played an important role in the formation of active sites.     

The influence of some synthesis parameters on Ziegler-Natta catalyst performance

The role of di-n-butyl ether (DBE) in the synthesis of highly active and stereospecific catalyst for propylene polymerization has been investigated. The ether was used as internal base (IB) or complexed with TiCl₄ and diethylaluminium chloride (DEAC) in iso-octane solution (System A) or complexed with triethylaluminium (TEA) in toluene solution (System B). Many differences were observed in the catalyst performance. The activity, the catalyst stereospecificity and the polymer bulk density were evaluated.     

Control of molecular weight distribution for polypropylene obtained by a commercial Ziegler–Natta catalyst: Effect of a cocatalyst and hydrogen

The polymerization of propylene was carried out with an MgCl₂‐supported TiCl₄ catalyst (with diisobutyl phthalate as an internal donor) in the absence and presence of hydrogen (H₂) as a chain‐transfer agent. Different structures of alkylaluminum were used as cocatalysts. The effects of the alkyl group size of the cocatalyst, H₂ feed, and feed time on the propylene polymerization behaviors were investigated. The catalyst activity significantly decreased with increasing alkyl group size in the cocatalyst. The molecular weight and polydispersity index (PDI) increased with increasing alkyl group size. With the introduction of H₂, the catalyst activity increased significantly, whereas the molecular weight and PDI of polypropylene (PP) decreased. Additionally, the effect of the polymerization time in the presence of H₂ on the propylene polymerization was studied. The molecular weight distribution curve was bimodal at short polymerization times in the presence of H₂, and we could control the molecular weight distribution of PP by changing the polymerization time in the presence of H₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Acyclic diene metathesis (ADMET) oligomerization of divinyltetramethyldisiloxane in the presence of rhodium and ruthenium complexes

Acyclic diene metathesis (ADMET) polymerization of divinyltetramethyldisiloxane in the presence of rhodium [RhCl(COD)]₂ and ruthenium RuCl₂(PPh₃)₃ catalysts led predominantly to linear oligomers [M _n=1815,M _w/M _n=1.16] if the rhodium catalyst was used or to mixtures of dimeric and trimeric oligomers if the ruthenium complex was applied. The rhodium complex appeared to be the first effective catalyst for ADMET polymerization of divinyldisubstituted organosilicon compounds.Part 14 in the series Metathesis of Silicon-Containing Olefins: for Part 13, see Ref. 8.     

Novel MgCl2-supported catalyst containing diol dibenzoate donor for propylene polymerization

A novel MgCl₂-supported Ziegler-Natta catalyst containing 2-isoamyl-2-isopropyl-1,3-propandiol dibenzoate donor for propylene polymerization was studied, and compared with catalysts with different internal donors, such as benzoate, phthalate and diether, in polymerization dynamic behavior, activity, hydrogen response and stereospecificity. It was found that there are two highly isospecific active sites in the catalyst with dibenzoate internal donor system and the effections of temperature are different on the performances of the two highly isospecific sites.     

Polymerization of olefins through heterogeneous catalysis XI: Gas phase sequential polymerization kinetics

A unique series of ethylene and propylene sequential polymerization experiments have been carried out in a stirred bed gas phase reactor using unsupported Stauffer AA catalyst (TiCl₃· $\frac{1}{3}$AlCl₃). Several interesting kinetic results were observed. It was found that propylene causes rate enhancement for a subsequent ethylene polymerization but that ethylene causes a rate reduction for a subsequent propylene polymerization. Furthermore, the rate enhancement/reduction effect increases with the duration of the preceding polymerization. Chemical/kinetic effects were found to be the likely causes of both the rate enhancements and the rate reductions observed during sequential polymerization. It was also shown that enhanced monomer sorption caused by the presence of a more soluble component, such as a heavier comonomer, does contribute to rate enhancement during simultaneous copolymerizations, but is not a factor for sequential polymerizations. © 1993 John Wiley & Sons, Inc.     

Effects of Reducibility on Propane Oxidative Dehydrogenation over γ-Al2O3-Supported Chromium Oxide-Based Catalysts

Alumina-supported chromium oxide and binary mixed oxide catalysts of the form Cr–M oxide/-Al₂O₃ (where M is Ni, Co, Mo, W, Ho, La, Li, Cs or Bi) were found to catalyze the oxidative dehydrogenation of propane at 300-450 °C. The basic characters of the metals were found to determine partly the selectivity to propylene. Cr–Mo/-Al₂O₃ proved to be the most promising. It exhibited a propylene yield of 10.3% at 450 °C. The connections between the selectivity and reducibility of the catalyst were explored. TPR results showed that addition of molybdenum to chromium increased the temperature of reduction maxima. Thus the selectivity to propylene was improved by a decrease in the tendency of the catalyst to undergo a redox cycle. Further, an X-ray photoelectron spectroscopy study conducted on a sample of the catalysts showed that the basicity of the catalysts increased with increase in molybdenum. Catalysts with appropriate Cr/Mo ratios exhibited lower selectivity to over-oxidation product than those containing either chromium or molybdenum alone.     

Polymerization of propylene using the high‐activity Ziegler–Natta catalyst system SiO2/MgCl2 (ethoxide type)/TiCl4/Di‐n‐butyl phthalate/triethylaluminum/dimethoxy methyl cyclohexyl silane

The bisupported Ziegler–Natta catalyst system SiO₂/MgCl₂ (ethoxide type)/TiCl₄/di‐n‐butyl phthalate/triethylaluminum (TEA)/dimethoxy methyl cyclohexyl silane (DMMCHS) was prepared. TEA and di‐n‐butyl phthalate were used as a cocatalyst and an internal donor, respectively. DMMCHS was used as an external donor. The slurry polymerization of propylene was studied with the catalyst system in n‐heptane from 45 to 70°C. The effects of the TEA and H₂ concentrations, temperature, and monomer pressure on the polymerization were investigated. The optimum productivity was obtained at [Al]/[DMMCHS]/[Ti] = 61.7:6.2:1 (mol/mol/mol). The highest activity of the catalyst was obtained at 60°C. Increasing the H₂ concentration to 100 mL/L increased the productivity of the catalyst, but a further increase in H₂ reduced the activity of the catalyst. Increasing the propylene pressure from 1 to 7 bar significantly increased the polymer yield. The isotacticity index (II) decreased with increasing TEA, but the H₂ concentration, temperature, and monomer pressure did not have a significant effect on the II value. The viscosity‐average molecular weight decreased with increasing temperature and with the addition of H₂. Three catalysts with different Mg/Si molar ratios were studied under the optimum conditions. The catalyst with a Mg/Si molar ratio of approximately 0.93 showed the highest activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1177–1181, 2003     

Ethylene and Propylene Polymerization Using In Situ Supported Me2Si(Ind)2ZrCl2 Catalyst: Experimental and Theoretical Study

Summary: Me₂Si(Ind)₂ZrCl₂ was in situ immobilized onto SMAO and used for ethylene and propylene polymerization in the presence of TEA or TIBA as cocatalyst. The catalytic system Me₂Si(Ind)₂ZrCl₂/SMAO exhibited different behavior depending on the amount and nature of the alkylaluminum employed and on the monomer type. The catalyst activity was nearly 0.4 kg polymer · g cat^?1 · h^?1 with both cocatalysts for propylene polymerization. Similar activities were observed for ethylene polymerization in the presence of TIBA. When ethylene was polymerized using TEA at an Al/Zr molar ratio of 250, the activity was 10 times higher. Polyethylenes made by in situ supported or homogeneous catalyst systems had practically the same melting point (T_m). On the other hand, poly(propylenes) made using in situ supported catalyst systems had a slightly lower T_m than poly(propylenes) made using homogeneous catalyst systems. The nature and amount of the alkylaluminum also influenced the molar mass. The poly(propylene) molar mass was higher when TIBA was the cocatalyst. The opposite behavior was observed for the polyethylenes. Concerning the alkylaluminum concentration, the molar mass of the polymers decreased as the amount of TEA increased. In the presence of TIBA, the polyethylene's molar mass was almost the same, independent of the alkylaluminum concentration, and the poly(propylene) molar mass increased with increasing amounts of cocatalyst. The deconvolution of the GPC curves showed 2 peaks for the homogeneous system and 3 peaks for the heterogeneous in situ supported system. The only exception was observed when TEA was used at an Al/Zr molar ratio of 500, where the best fit was obtained with 2 peaks. Based on the GPC deconvolution results and on the theoretical modeling, a proposal for the active site structure was made.

Molar mass distribution deconvolution of polyethylene prepared with the system Me₂Si(Ind)₂ZrCl₂/SMAO/TIBA with 500 mol/mol of alkylaluminum as cocatalyst.     

Porous versus novel compact Ziegler–Natta catalyst particles and their fragmentation during the early stages of bulk propylene polymerization

The effect of the porosity of Ziegler–Natta catalyst particles on early fragmentation, nascent polymer morphology, and activity were studied. The bulk polymerization of propylene was carried out with three different heterogeneous Ziegler–Natta catalysts under industrial conditions at low temperatures, that is, with a novel self‐supported catalyst (A), a SiO₂‐supported catalyst (B), and a MgCl₂‐supported catalyst (C), with triethyl aluminum as a cocatalyst and dicyclopentyl dimethoxy silane as an external donor. The compact catalyst A exhibited no measurable porosity and a very low surface area (<5 m²/g) by Brunauer–Emmet–Teller analysis, whereas catalysts B and C showed surface areas of 63 and 250 m²/g, respectively. The surface and cross‐sectional morphologies of the resulting polymer particles at different stages of particle growth were analyzed by scanning electron microscopy and transmission electron microscopy. The compact catalyst A showed homogeneous and instantaneous fragmentation already in the very early stages of polymerization, which is typically observed for porous MgCl₂‐supported Ziegler–Natta catalysts. Moreover, the compact catalyst particles gave rise to almost perfectly spherical polymer particles with a smooth surface. In contrast, the silica‐supported catalyst B gave rise to particles having a cauliflower morphology, and the second reference catalyst C produced fairly spherical polymer particles with a rough surface. All of the three catalysts exhibited similar activities of 450 g of polypropylene/g of catalyst after 30 min of polymerization, and most interestingly, the comparative kinetic data presented indicated that the reaction rates were not influenced by the porosity of the catalyst. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

Polymers of propylene and higher 1-alkenes produced with post-metallocene complexes containing a saligenin-type ligand

Polymerization reactions of propylene and three higher linear 1-alkenes, 1-hexene, 1-octene and 1-decene, were carried out with post-metallocene catalysts derived from Ti complexes I and II with a bidentate phenol-alcohol (saligenin-type) ligand derived from 2,4-di-tert-butyl-6-(1,1,1,3,3,3-hexafluoro-2-hydroxy-propan-2-yl)phenol, in the presence of two cocatalysts, MAO and a combination of AlEt₂Cl and MgBu₂. All catalyst systems contain a large variety of active centers and produce both amorphous atactic polymers and partially crystalline isotactic material. The AlEt₂Cl-MgBu₂ cocatalyst produces significantly more active catalyst systems. Analysis of ¹³C NMR data for the propylene polymers shows that the mechanism of isotactic chain growth is principally different for the active centers formed in the presence of the two cocatalysts.     

Preparation of bimodal polypropylene in two‐step polymerization

Polymerization of propylene was carried out by using MgCl₂.EtOH.TiCl₄.DIBP.TEA.cHMDMS catalyst system in n‐heptane, where MgCl₂, EtOH, TiCl₄, DIBP (diisobutyl phthalate), TEA (triethyl aluminum), and cHMDMS (cyclohexyl methyl dimethoxy silane) were support, ethanol for alcoholation, catalyst, external donor, cocatalyst (activator), and internal donor, respectively. The catalyst activity and polymer isotacticity were studied by measuring the produced polymer and its solubility in boiling n‐heptane, respectively. The molecular weight and molecular weight distribution of the polymers were evaluated by gel permeation chromatography. Hydrogen was used for controlling the molecular weight. For producing the bimodal polypropylene, the polymerization was carried out in two steps (i.e., in the presence and absence of hydrogen). It was found that the catalyst showed high activity and stereoselectivity, on the other hand, bimodal polymer could simply be produced in two‐step polymerization by using MgCl₂.EtOH.TiCl₄.DIBP.TEA.cHMDMS catalyst system. Meanwhile, the effect of the step of the hydrogen adding on propylene polymerization was investigated. It was shown that the addition of hydrogen in the second step was more suitable. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1456–1462, 2006     

Evaluation of the effect of reaction and mass transfer on the growth of polymer particles in olefin polymerization

The process of the growth of polymer particles in olefin polymerization is studied. The regions of the possible overheating of particles due to the polymerization reaction in the gas and liquid phases of a monomer and in a solvent are estimated. It is shown how the rates of external mass transfer, internal diffusion, and reaction in the polymer particle vary with its growth. The cause of unusual transition of the reaction from the diffusion region to the kinetic one with the growth of particles is clearly explained. A model for the dynamics of the polymerization process is proposed that takes into account the diffusion of active component ions of a catalyst (chlorine in Ti _x Cl _y and oxygen in Cr _x O _y ). The results of the study are used in the application of high-activity catalysts to the slurry process of propylene polymerization.     

Selective synthesis of isobutene trimers and hexamers with oxo acid catalysts

The reaction of isobutene (IB) with its dimers (IB₂) catalyzed by CF₃SO₃H yielded isobutene trimers (IB₃) in high yield in nonpolar solvents at 0°C. The initial feed of isobutene, in the presence of equimolar IB₂ or more, was selectively converted into IB₃ without loss or accumulation of IB₂. After complete consumption of the isobutene, however, the remaining IB₂ rapidly dimerized to isobutene tetramers (IB₄). ¹³C-NMR analysis of the products showed that the IB₃ was formed via addition of the t-butyl cation (protonated isobutene to 2,4,4-trimethyl-1-pentene (an IB₂ isomer); the trimer fraction was free from isomers arising from addition of the t-butyl cation to 2,4,4-trimethyl-2-pentene (another IB₂ isomer) or addition of the IB₂ cation to isobutene. The IB₃ thus obtained was further oligomerized with CF₃SO₃H catalyst in nonpolar media in the range of 0 to ?25°C to give a mixture of IB₅, IB₆, and IB₇ in high yield. With EtAlCl₂ as catalyst, reaction of isobutene with IB₂ and oligomerization of IB₃ both resulted in products with a broad molecular weight distribution containing higher oligomers and complex hydrocarbons formed via cracking of the intermediate carbocations.     

The activity of molybdenum and molybdenum oxide model catalysts for olefin metathesis

The activity of various molybdenum oxides supported on a molybdenum foil substrate for the catalysis of propylene metathesis is measured using an isolatable, high-pressure reactor incorporated in an ultra-high vacuum (UHV) chamber which allows samples to be transferred directly from vacuum into the catalytic test chamber. MoO _x samples are prepared both by oxidation of metallic molybdenum and reduction of molybdenum trioxide. The results suggest that the presence of an oxygen overlayer on the catalyst inhibits reaction and that the ranking of activity for metathesis at 870 K using 450 Torr of propylene for oxide samples is MoO₂>MoO₃>Mo where MoO₂ is 30 times more active than molybdenum metal under these conditions.