Control of molecular weight distribution for polypropylene obtained by commercial Ziegler–Natta catalyst: effect of temperature

Polymerization of propylene was carried out by using MgCl₂-supported TiCl₄ catalyst in conjunction with triethylaluminium (TEA) as cocatalyst. The effect of polymerization temperature on polymerization of propylene was investigated. The catalyst activity was influenced by the polymerization temperature significantly and the maximum activity of the catalyst was obtained at 40 °C. With increasing the polymerization temperature, the molecular weight of polypropylene (PP) drastically decreased, while the polydispersity index (PDI) increased. The effect of the two-stepwise polymerization procedure on the molecular weight and molecular weight distribution of PP was studied and the broad PDI of PP was obtained. It was also found that the PDI of PP could be controlled for propylene polymerization through regulation of polymerization temperature. Among the whole experimental cases, the M _w of PP was controlled from 14.5 × 10⁴ to 75.2 × 10⁴ g/mol and the PDI could be controlled from 4.7 to 10.2.     

High temperature polymerization of propylene catalyzed by MgCl2‐supported Ziegler–Natta catalyst with various cocatalysts

Four cocatalysts, referred to as ethylaluminoxanes, were synthesized by the reaction between triethylaluminium (AIEt₃) and water under various molar ratios of H₂O/Al at ?78°C. Aluminoxanes were used as cocatalysts for a MgCl₂‐supported Ziegler–Natta catalyst for propylene polymerization at temperatures ranging from 70 to 100°C. When the polymerization was activated by AlEt₃, the activity as well as the molecular weight and isotacticity of the resulting polymer gradually dropped as the temperature varied from 70 to 100°C. When ethylaluminoxane was employed as the cocatalyst, good activity and high molecular weight and isotacticity were obtained at 100°C. Furthermore, when the cocatalyst varied from AlEt₃ to ethylaluminoxane, the atactic fraction and polymer fraction with moderate isotacticity decreased and the high isotactic fraction slightly increased, which indicated that the variation of the cocatalyst significantly affects the isospecificity of active sites. It was suggested that the reactivity of the Al‐Et group and the size of the cocatalyst were correlated to the performance of the Ziegler–Natta catalyst at different temperatures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1978–1982, 2006     

The influence of combined external donor and combined cocatalyst on propylene polymerization with a MgCl2‐supported Ziegler–Natta catalyst in the presence of hydrogen

The influence of combined external donor (ED) (diphenyldimethoxysilane/dicyclopentyldimethoxysilane) and combined cocatalyst (triethylaluminum/triisobutylaluminum) on propylene polymerization with MgCl₂‐supported Ziegler–Natta catalyst in the presence of hydrogen was investigated. By deconvolution analysis of the molecular weight distribution (MWD) into multiple Flory components, the influence of ED and cocatalyst on the active center distribution of the catalyst was demonstrated, and the mechanism was discussed. Using combined cocatalyst and combined donor, iPP with high molecular weight, high isotacticity index, and broad MWD can be obtained. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41689.     

Effect of polymerization conditions on the polymer properties of CO2-cyclohexene oxide copolymer prepared by double metal cyanide catalyst

The effect of polymerization parameters such as polymerization time, temperature, pressure and the amount of catalyst amount in CO₂-cyclohexene copolymerizations with double metal cyanide (DMC) catalyst were investigated in detail. Especially, the effect of polymerization conditions on the polydispersity index (PDI) and glass transition temperature (T_g) were deeply examined. Increases in polymerization time, pressure, temperature and the amount of catalyst in feed increased the activity of the DMC catalyst. The molecular weight (MW), PDI and glass transition temperature (T_g) were affected by the polymerization time, temperature, pressure and the amount of catalyst in the feed.     

Organometallics in ethylene polymerization with a catalyst system TiCl4/Al(C2H5)2Cl/Mg(C6H5)2: 2. Polymerization process in pseudo-solution

A study has been made of ethylene polymerization in pseudo-solution with a catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂ in the presence of hydrogen as a regulator of polyethylene molecular weight. The polymerization process in pseudo-solution by adjustment of hydrogen makes it possible to produce polyethylene having a wide range of molecular weights. For this purpose melt indices between 0°–50°C/min are desirable and these values are not reached with a suspension type of ethylene polymerization with a catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂. The effect of the molar ratio cocatalyst/catalyst (Al/Ti and Mg/Ti) on the catalyst activity and on the polyethylene molecular weight was studied, together with the content of hydrogen as a regulator of the molecular weight. The catalyst productivity increased to some limiting molar ratio Mg/Ti and Al/Ti and further increase of organometallics in the catalyst system did not influence the polymer molecular weight. In the case of ethylene polymerization with this catalyst combination in the presence of hydrogen, some activation of the catalyst was observed. Two mechanisms, which may account for the activation effect of the hydrogen are discussed.     

Improving microisotacticity of Ziegler–Natta catalyzed polypropylene by using triethylaluminum/triisobutylaluminum mixtures as cocatalyst

Propylene was polymerized with TiCl₄/Di/MgCl₂ catalyst and cocatalysts containing triethylaluminum (TEA) and triisobutylaluminum (TiBA) in the presence of Ph₂Si(OMe)₂ (external donor) and hydrogen. Chain structure of the formed polypropylene (PP) was characterized by temperature-rise elution fractionation (TREF) combined with DSC and ¹³C NMR analysis of the main fractions. Increasing the amount of TiBA in cocatalyst leads to decrease of isotactic index of PP, meanwhile the microisotacticity of the main TREF fractions of PP was enhanced. PP produced with the catalyst activated by a 50/50 TEA/TiBA mixture has the same content of highly isotactic chains as PP produced with the TEA activated catalyst, but main TREF fractions of the former has higher microisotacticity than the later. Fast alkyl exchanges in TEA/TiBA mixtures are found by ¹H NMR analysis of the mixtures. By analyzing alkanes released from hydrolyzed catalysts that have been treated with the cocatalyst, alkylation power of TEA/TiBA mixture was found to decrease with increasing its TiBA content. The effects of TEA/TiBA mixture in propylene polymerization is explained by the weaker alkylation power and lower Lewis acidity of the mixed alkylaluminums than pure TEA. Decrease in the alkylation power leads to reduction of active centers with the highest stereospecificity, meanwhile decrease in Lewis acidity intensified the role of De in enhancing stereospecificity of different active centers. When the amount of TiBA in TEA/TiBA mixture falls in a suitable range, the later effect becomes dominant, and evident improvement in microisotacticity of PP can be achieved.     

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     

Effect of the cocatalyst on the copolymerization of ethylene and propylene with high activity Ziegler-Natta catalyst

Summary Ethylene and propylene were copolymerized in n-heptane in the presence of high activity heterogeneous Ziegler-Natta catalyst to study the effect of the cocatalyst on the microstructure and molecular weight of the copolymer. Seven aluminium alkyls of structure Al((CH₂)_nCH₃)₃, where n = 0—3, 5, 7 or 11, and one of structure Al(C(CH₃)₃)₃, were used as cocatalysts. The effect of the Al/Ti mole ratio was also studied. Modern molecular modelling techniques were used to calculate the volume of the cocatalyst and the electron density around aluminium. The size of the cocatalyst molecule was found to have a marked effect on the activity of the catalyst: the smaller the cocatalyst the higher the activity. Higher electron density around aluminium increased the randomness of the copolymer.     

On the role of catalyst components in the living metathesis polymerization of substituted acetylenes by MoOCl4-based systems

Summary The role of components in MoOCl₄-based living polymerization catalysts was studied. The MALDI TOF MS spectra of the poly(o-[(trifluoromethyl)phenyl]acetylene)s prepared with n-Bu₄Sn and Et₃Al as cocatalysts suggested a difference of 28(C₂H₄) in polymer molecular weight. This indicates that the formed polymer possesses an alkyl group of cocatalyst in the initiating chain end, which implies the transalkylation between MoOCl₄ and a cocatalyst and the subsequent formation of a Mo carbene. Sterically uncrowded aliphatic alcohols were useful as the third catalyst components. Addition of EtOH to the catalyst system led to the increase of activation enthalpy and the change of activation entropy from a negative to positive value in the propagation reaction, which suggests that EtOH coordinates to the propagating end competitively with the monomer. Received: 10 December 1999/Revised version: 3 February 2000/Accepted: 7 February 2000     

Temperature effect on ethylene polymerization with a catalyst prepared by mixing Mg(C2H5)(n-C4H9), Al(C2H5)1.5Cl1.5 and iron(II)bis (imino)pyridyl complex

Summary Ethylene polymerization was conducted with a catalyst prepared by mixing 2,6-bis{1-[2,6-(diisopropylphenyl)imino]ethyl}pyridine iron dichloride, Mg(C₂H₅)(n-C₄H₉) and Al(C₂H₅)_1.5Cl_1.5 in the presence of common alkylaluminium as cocatalyst. Both the activity and the molecular weight of polymers produced were markedly dependent upon the polymerization temperature. The end-group analysis of polymers showed that the molecular weight of polymers produced at higher temperature was reduced by chain transfer with Al(C₂H₅)₃ in addition to β-hydrogen elimination.     

POLYMERIZATION KINETICS AND MODELING OF SLURRY ETHYLENE POLYMERIZATION PROCESS WITH METALLOCENE/MAO CATALYSTS

Polymerization methods of ethylene include the slurry, solution, and gas-phase processes. This study investigates polymerization conditions and kinetics under slurry process. Typical metallocene catalyst/cocatalyst Cp₂ZrCl₂/MAO system was used for ethylene polymerization. Two kinds of polymerization kinetics were compared in this study, multiple active-site model and transfer-effect model. The kinetic studies used metallocene-type polymerization kinetics, including catalyst activation, initiation, chain propagation, chain transfer, and termination steps. In addition, kinetic constants of polymerization reaction model were calculated. Calculation results of catalyst activity and molecular weight were compared with experimental results, indicating their good correlation. Moreover, the conventional polymerization was modified to accurately predict the molecular weight behaviors under various reaction conditions with the proposed transfer-effect model. Exactly, how reaction time, pressure, catalyst concentration, and cocatalyst ratio affect catalyst activity and molecular weight of the polymer were also discussed.     

In situ synthesis of polybutene‐1/polypropylene spherical alloys within a reactor with an MgCl2‐supported Ziegler–Natta catalyst

A series of isotactic polybutene‐1/polypropylene (PB/PP) alloys with spherical morphology were prepared by MgCl₂‐supported Ziegler‐Natta catalyst with sequential two‐stage polymerization technology. The first formed PP particles were used as micro‐reactors to initiate the bulk precipitation polymerization of butene‐1 further. The porous PP particles as a hard framework may prevent the adhesion of PB particles during the bulk precipitation polymerization process. At the same time, the bulk precipitation polymerization process allows for maximization of the butene‐1 polymerization rate and simplifies the butene‐1 polymerization process considerably. Finally, spherical PB alloys with a super‐high molecular weight PB component and adjustable PP component were synthesized in situ within the reactor. The structures and properties of the PB/PP alloys were characterized by gel permeation chromatography, ¹³C nuclear magnetic resonance, Fourier transform IR, scanning electron microscopy, differential scanning calorimetry and X‐ray diffraction. The results showed that the MgCl₂‐supported Ziegler‐Natta catalyst showed relatively high stereospecificity and efficiency for both propylene and butene‐1 polymerization. The incorporation of propylene on the PB matrix affects the properties of the final products markedly. The PB/PP alloys are expected to have a broader range of applications as a new family of high performance materials. Copyright © 2012 Society of Chemical Industry     

N-(n-Alkyl)-2-pyridinemethanimine mediated atom transfer radical polymerization of lauryl methacrylate: Effect of length of alkyl group

The article describes the polymerization of lauryl methacrylate (LMA) using Cu(I)Br as catalyst for atom transfer radical polymerization in conjunction with N-(n-propyl) [PPMI]/(n-hexyl) [HPMI]/(n-octyl) [OPMI]-2-pyridinemethanimine as complex ligands. The polymerization of LMA was investigated in bulk and solution (toluene as solvent) using Cu(I)Br as catalyst, N-(n-alkyl)-2-pyridinemethanimine as ligands and ethyl-2-bromo isobutyrate (EBiB) as initiator. The ratio of LMA : CuBr : Ligand : EBiB was kept constant in all the polymerizations. In bulk polymerization, the solubility of the catalyst complex increased with increasing the length of alkyl chain on the ligand from propyl to octyl and also gave polymers with narrow molecular weight distribution. The PDI was further narrowed by using OPMI as ligand and toluene was used as solvent. The kinetics of polymerization was also analyzed and it clearly shows that % conversion increased with time. Increase in molecular weight with % conversion without affecting PDI clearly show that the system is living and living nature can be controlled by increasing the length of alkyl group. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Polymerization of propylene using a prepolymerized high-active Ziegler–Natta catalyst. I. Kinetic studies

The kinetics of propylene polymerization using a prepolymerized high-active TiCl₃ catalyst with an Et₂AICI cocatalyst are investigated. The effect of various parameters such as AI/Ti ratio, pressure, temperature, hydrogen, and polymerization time on the rate of polymerization and yield are examined. The dependency of these parameters on the polymerization rate are studied. It is found that the variation at the rate of polymerization with the Et₂AICI cocatalyst concentration complies with a Langmuir–Hinshelwood type of relationship. The overall activation energy of polymerization calculated from the Arrhenius plot was found to be 11.6 kcal/mol. © 1996 John Wiley & Sons, Inc.     

Propene polymerization with MgCl2-supported TiCl4/dioctylphthalate catalyst. III. Effects of polymerization conditions on molecular weights and molecular weight distribution

In propene polymerization over the MgCl₂-supported TiCl₄/dioctylphthalate (DOP) catalyst, the weight- and number-average molecular weights and the molecular weight distribution (MWD) of polypropene products and of the isotactic and atactic polymer portions were studied. The average molecular weights and MWD were found to be independent of time. The isotactic polymer had higher molecular weight and broader distribution than the atactic portion by almost an order of magnitude. An increase in temperature and cocatalyst/catalyst ratio resulted in lowering molecular weight due to increasing transfer reaction. Alkyl aluminum was used as a cocatalyst, and the molecular weight did not vary significantly with different alkyl groups. Of the three external bases studied, 2,2,6,6-tetramethyl piperidine (TMPIP), dimethoxydiphenyl silane (DMDPS), and t-butylmethyl ether (TBME), the addition of a small amount of one of the first two bases caused a substantial increase in both molecular weight and polydispersity of the isotactic polymer. Those increases leveled off quickly with increasing amounts of the external base. On the other hand, both average molecular weights and polydispersity of the atactic polymer decreased with a net increase in the molecular weight of the whole polymer. TBME, however, has no significant effect on either molecular weight or MWD. These effects are discussed in the context of the roles of the external base in propene polymerization. © 1995 John Wiley & Sons, Inc.     

钒化合物催化活化体系乙丙三元共聚合研究

采用自制的钒化合物为主催化剂,倍半烷基铝为助催化剂,三氯乙酸乙酯为活化剂,对乙烯、丙烯、乙叉降冰片烯三元共聚合进行了研究,结果表明,当活化剂采用三氯乙酸乙酯时乙丙三元共聚合活性要高于其它活化剂,在活化剂存在条件下,当活化剂与钒催化剂的物质的量比为12、催化剂用量为0.06mmol/(100 mL己烷)、铝比n(Al)/n(V)=40、聚合温度为常温时,乙丙三元聚合活性可提高3.1倍左右。     

Preparation of ultra high molecular weight polyethylene with MgCl<Subscript>2</Subscript>/TiCl<Subscript>4</Subscript> catalyst: effect of internal and external donor on molecular weight and molecular weight distribution

Ultra high molecular weight polyethylene (UHMWPE) was prepared by using MgCl₂-supported TiCl₄ catalyst in conjunction with triethylaluminium (TEA) cocatalyst. The effects of internal and external donor on polydispersity index (PDI) of UHMWPE were investigated. The catalyst activity with various kinds of internal donor decreased in the following order: none > succinate > phthalate > diether, while the catalyst activity was less influenced by the structure of external donor. The PDI of UHMWPE was examined by using gel permeation chromatography (GPC) analysis and/or rheometry measurements. The PDI obtained by rheometer was matched with the results obtained by GPC within an error of max. 20%. The highest molecular weight and PDI of UHMWPE were obtained by the catalyst of succinate as internal donor. It was also observed that the molecular weight and PDI of UHMWPE were less affected by the introduction of external donor.     

Polymerization of propylene with TiCl3–AlEt2Cl–trilauryltrithiophosphite catalyst

AlEt₃Cl was modified with TLTTP (trilauryltrithiophosphite) in the catalyst system consisting of TiCl₃ and AlEt₂Cl. The effects of TLTTP on the polymerization of propylene were studied in comparison with those of alkyl homologues of TLTTP. The catalytic behavior of the TiCl₃–AlEt₂Cl-TLTTP catalyst system in the polymerization of propylene was also studied in comparison with that of the TiCl₃–AlEt₂Cl catalyst system. In the study of the effect of various alkylthiophosphites added, it is found that the bulkiness of the alkyl group affects the rate of propylene polymerization and the stereoregularity of the resultant polymers. The TiCl₃–AlEt₂Cl–TLTTP catalyst system gave different catalytic behavior in the propylene polymerization from that of the unmodified conventional catalyst system (TiCl₃–AlEt₂Cl). These effects of TLTTP were considered to be due to the bulkiness of the alkyl groups attached to the phosphorous atom and the higher reactivity to TiCl₃ of the modified AlEt₂Cl than of the unmodified AlEt₂Cl.     

Polymerization of vinyl ethers using titanium catalysts containing tridentate triamine ligand of the type N[CH2CH(Ph)(Ts)N]2

Titanium complexes having tridentate triamine of the type N[CH₂CH(Ph)(Ts)N]₂²⁻ in combination with methylaluminoxane (MAO) was able to polymerize ethyl vinyl ether in good yields. The polymers obtained in general were having molecular weight in the order of 10⁵ with narrow molecular weight distributions. Polymerization conditions had an impact on the molecular weight and the polydispersity index (PDI). Using chlorobenzene as the solvent the polymer had an M_n of 350?000 and PDI of 1.21, where as under neat conditions the M_n was 255?000 with PDI of 1.21. The type of solvent and the temperature dictated the polymerization rate and the polymer stereo regularity. The molecular weight of the polymer is distinctly governed by the polymerization temperature. Temperature ranging between −50 and ambient (30 °C) resulted in high molecular weight polymers and vice versa at a temperature of 60-70 °C resulted in low molecular weight polymers in moderate yields. The polymers obtained below 30 °C are highly stereo-regular compared to that of the ones produced at and above ambient temperature. The polymerization of iso-butyl vinyl ether (IBVE) was faster than that of linearly substituted n-butyl vinyl ether (BVE) and less bulky ethyl vinyl ether (EVE). The order of isotacticities of the polymers obtained are polyIBVE > polyBVE > polyEVE. The use of borate cocatalyst for activation generated narrow molecular weight polymers with a linear increase in the yield and molecular weight over time suggesting the living nature of the catalyst system.