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     

Ethylene polymerization using a novel MgCl2/SiO2‐supported Ziegler–Natta catalyst

A novel MgCl₂/SiO₂‐supported Ziegler–Natta catalyst was prepared using a new one‐pot ball milling method. Using this catalyst, polyethylenes with different molecular weight distributions were synthesized. The effects of the [Si]/[Mg] ratio, polymerization temperature and [Al]/[Ti] ratio on the catalytic activity, the kinetic behaviour and the molecular weight and the polydispersity of the resultant polymer were studied. It was found that the polydispersity index of the polymer could be adjusted over a wide range of 5–30 through regulating the [Si]/[Mg] ratio and polymerization temperature, and especially when the [Si]/[Mg] ratio was 1.70, the polydispersity index could reach over 25. This novel bi‐supported Ziegler–Natta catalyst is thus useful for preparing polyethylene with a required molecular weight distribution using current equipment and technological processes. Copyright © 2005 Society of Chemical Industry     

An approach for complete molecular weight distribution calculation: Application in ethylene coordination polymerization

The objective of this article is to present an approach to ascertain the molecular weight distribution (MWD) of polymeric systems and its application to an industrial polyethylene reactor. Ascertaining the complete MWD can provide more reliable predictions of polymer end‐use properties, as some of them may depend on specific molecular weight ranges, instead of solely on the averages of the distribution. The proposed method is based on differentiation of the cumulative MWD, where the accumulated concentrations, evaluated at a finite number of chain lengths, are considered components in a reaction medium. Therefore, the dimension of the mathematical model may be suited to the desired level of detail on the MWD. The ethylene polymerization in solution with Ziegler–Natta catalyst is taken as a case study because of the lack of studies in this field. The reaction takes place in continuously stirred and tubular reactors. The results show the potential of the proposed approach and its usefulness in ascertaining the whole MWD, which in turn can be used to predict the polymer end‐use properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study of the kinetics,mass transfer,and particle morphology in the production of high‐impact polypropylene

A sequence of experimental steps was perfected to produce high‐impact modified polypropylene (PP), and to study the influence of particle morphology and rubber content on the reaction kinetics, especially in terms of mass transfer limitations. It was found that after a critical copolymer content at approximately 40% (with respect to total weight), it was impossible to obtain high reaction rates. This is thought to be the result of a fundamental change in particle morphology attributed to the presence of a soft EPR copolymer phase in the micropores. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1047–1060, 2001     

MgCl2‐supported TiCl4 catalysts containing diethyl norbornene‐2,3‐dicarboxylate internal electron donor for 1‐butene polymerization: Effects of internal electron donor configuration

Three isomeric 5‐norbornene‐2,3‐dicarboxylic acid diethyl ester (NDDE) with endo‐, exo‐, and trans‐configuration have been synthesized and employed as internal electron donors (IED) in 1‐butene polymerization over magnesium chloride supported Ziegler–Natta catalysts. It was found that the configuration of NDDE plays a key role in tuning the catalyst activity, stereospecificity, molecular weight (MW), and polydispersity index (PDI) of resulting poly(1‐butene). The type of catalyst with cis‐5‐norbornene‐endo‐2,3‐dicarboxylic acid diethyl ester as IED shows the highest catalyst activity, while catalyst with trans‐NDDE as IED yields the poly(1‐butene) with the highest MW and the most broad PDI. IR results showed that the NDDE with endo‐, exo‐, and trans‐configuration have different coordination way to MgCl₂, subsequently affecting the catalysts performance. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40758.     

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     

Sorption studies of propylene in polypropylene. Diffusivity in polymer particles formed by different polymerization processes

Propylene was polymerized in gas phase and liquid phase by using a novel nonporous Ziegler–Natta‐catalyst system. The polymer particles formed at different polymerization times were used for sorption measurements. In both cases it was found that the effective diffusion coefficient is increasing with increasing size of polymer particles and the effective diffusion coefficients of polymer particles formed by liquid‐phase polymerization are larger than those of polymer particles produced by gas‐phase polymerization. The effective diffusion coefficients of polymer particles are in the range of 2 × 10^?11 to 1.6 × 10^?10 m²/s with activation energies from 34 to 22 kJ/mol. The analyzed polymer particles have average diameters between 250 and 875 μm. The solubility of propylene in polypropylene particles can be described by the law of Henry at conditions studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2642–2648, 2006     

Novel stabilization system for polypropylene via the Ziegler–Natta catalyzed polymerization in the presence of aluminum aryloxide

The aluminum aryloxide was prepared via the reaction of phenolic antioxidant, 3‐(3,5‐di‐t‐butyl‐4‐hydroxyphenyl)‐N‐octadecylpropionamide, with triethyl aluminum. Propylene polymerization using supported Ziegler–Natta catalyst systems was carried out in the presence of the antioxidant or its aluminum aryloxide. Although the antioxidant gave rise to decrease in catalyst yield and change in hydrogen response, the aluminum aryloxide had no influence on the catalytic polymerization behavior, and thus the obtained polymer characteristics such as molecular weight, polydispersity, and meso pentad as a stereoregularity were comparable to that polymerized without the antioxidant and the aluminum aryloxide. Polypropylene obtained in the presence of the aluminum aryloxide was well stabilized for oxidation and its stability was over 1000 h at 100°C (estimated to be over 30 years at room temperature). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1350–1358, 2006     

Control of molecular weight distribution in propylene polymerization with Ziegler–Natta/metallocene catalyst mixtures

Propylene polymerization was investigated with a sequential addition of Ziegler–Natta and metallocene catalysts. From the fact that the molecular weights of polypropylene (PP) produced with Ziegler–Natta and with metallocene catalysts differ, it was possible to control the molecular weight distribution (MWD) of PP with a sequential addition of methylaluminoxane and rac-ethylenebis(indenyl)zirconium dichloride followed by triethylaluminum and magnesium dichloride-supported titanium tetrachloride catalyst. The obtained PP exhibited a wide MWD curve with shoulder peak. The position and height of each peak was controlled with the variation of polymerization time for each catalyst as well as the amount of each catalyst. The MWD of PP prepared with sequential addition of catalysts was much wider than that of PP obtained from each catalyst. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2213–2222, 1998     

Effect of electron donors on 1,3‐butadiene polymerization by a Ziegler–Natta catalyst based on neodymium

High‐cis polybutadiene produced by catalyst systems based on a rare earth is an elastomer used to produce green tires. This type of tire presents lower rolling resistance, which allows higher fuel economy, and thus fewer chemical compounds are discharged into the atmosphere. In this work, the influence of electron donors [tetrahydrofuran (THF) and tetramethylethylenediamine (TMEDA)] present in the polymerization solvent on the microstructure and molecular weight characteristics of the polybutadiene produced by neodymium catalysts was studied. The catalyst synthesis was carried out in glass bottles for 1 h at a temperature between 5 and 10°C. The catalyst components were diisobutylaluminum hydride, neodymium versatate, and tert‐butyl chloride. The polymerization reaction was carried out for 2 h. The reaction temperature was kept at 70± 3°C. The addition of TMEDA or THF above a determined concentration reduced the catalytic activity, molecular weight, and concentration of cis‐1,4 units (<96%), whereas the polydispersity increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2539–2543, 2005     

Preparation of ultra‐high‐molecular‐weight polyethylene and its morphological study with a heterogeneous Ziegler–Natta catalyst

Ultra‐high‐molecular‐weight polyethylene (PE) with viscosity‐average molecular weight (M_v) of 3.1 × 10⁶ to 5.2 × 10⁶ was prepared with a heterogeneous Ziegler–Natta MgCl₂ (ethoxide type)/TiCl₄/triethylaluminum catalyst system under controlled conditions. The optimum activity of the catalyst was obtained at a [Al]/[Ti] molar ratio of 61 : 1 and a polymerization temperature of 60°C, whereas the activity of the catalyst increased with monomer pressure and decreased with hydrogen concentration. The titanium content of the catalyst was 2.4 wt %. The rate/time profile of the catalyst was a decay type with a short acceleration period. M_v of the PE obtained decreased with increasing hydrogen concentration and polymerization temperature. The effect of stirrer speeds from 100 to 400 rpm did not so much affect the catalyst activity; however, dramatic effects were observed on the morphology of the polymer particles obtained. A stirrer speed of 200 rpm produced PE with a uniform globulelike morphological growth on the polymer particles. The particle size distributions of the polymer samples were determined and were between 14 and 67 μm. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Investigation of kinetics of 4‐methylpentene‐1 polymerization using Ziegler–Natta‐type catalysts

The kinetics of 4‐methylpentene‐1 (4MP1) polymerization by use of Ziegler–Natta‐type catalyst systems, M(acac)₃‐AlEt₃ (M = Cr, Mn, Fe, and Co), are investigated in benzene medium at 40°C. The effect of various parameters such as Al/M ratio, reaction time, aging time, temperature, catalyst, and monomer concentrations on the rate of polymerization and yield are examined. The rate of polymerization increased linearly with increasing monomer concentration with first‐order dependence, whereas the rate of polymerization with respect to catalyst concentration is found to be 0.5. For all cases, the polymer yield is maximum at an Al/M ratio of 2. The activation energies obtained from linear Arrhenius plots are in the range of 25.27–33.51 kJ mol^?1. It is found that the aging time to give maximum percentage yield of the polymer varies with the catalyst systems. Based on the experimental results, a plausible mechanism is proposed that envisages a free‐radical mechanism. Characterization of the resulting polymer product, for all the cases, through FTIR, ¹H‐NMR, and ¹³C‐NMR studies, showed isomerized polymeric structures with 1,4‐structure as dominant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2468–2477, 2003     

Study on morphology of high impact polypropylene prepared by in situ blending

High impact polypropylene (HIPP) was prepared by in situ blending of isotactic polypropylene and ethylene–propylene rubber (EPR) with spherical Ziegler–Natta catalyst. Morphology and pore characteristics of such HIPP were investigated by scanning electron microscope, atomic force microscopy, and mercury intrusion. Amorphous phase was removed from polypropylene matrix and characterized by ¹³C NMR spectrum. It was found that the EPR prepared in this manner contained variable composition polymer chains with a distribution of ethylene and propylene sequence lengths. Final products of HIPP were free flowing, spherical granules. There were small pores in HIPP, which seemed not to be filled up, and could be determined by mercury intrusion even when the content of rubber was up to 24 wt %. Homopolypropylene with pore diameter between 100 and 10,000 nm was suitable for EPR to fill in during ethylene–propylene copolymerization. The block copolymer fractions act as a compatilizer between matrix and EPR. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1386–1390, 2006     

Fractal approach for modeling the morphology evolution of olefin polymerization with heterogeneous catalysts

Fractal theory and methodology were used to investigate the morphology of titanium–magnesium‐supported polyethylene catalysts and their relevant polymer particles. Through an analysis of the submicrostructures using scanning electron microscopy images, the surface fractal dimensions of the related particles were estimated with the box‐counting method. With consideration given to the fact that the growth process of a polymer is an evolving fractal process, which is controlled on the one hand by the initial conditions, including the initial fractal dimensions of the catalysts and the initial reaction conditions, and on the other hand by the previous morphology characteristics of the system, a novel polymerization fractal growth model was constructed. The simulation results showed good agreement with the experiment data. Moreover, the morphology evolution with the prepolymerization technique was predicted, and it was suggested that the duration of polymerization was 10–30 min. It was proven that the use of the surface fractal dimension as an important parameter describing the surface morphologies of the particles, either of catalysts or polymers, was real and effective. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1463–1470, 2003     

Effect of fatty amine and perfluorocarbon as anti‐fouling agent on the catalyst activity and titanium oxidation state in slurry polymerization of ethylene

In this work, the effect of two antifouling materials on the activity of catalyst used to produce polyethylene in a 1‐L slurry reactor and on the titanium oxidation state of the catalyst was investigated. Armostat 300 with the formula alkyl C₁₄‐C₁₈ bis(2‐hydroxyethyl)amine is an antistatic agent that reduces static electricity of the polymer particles. It was found that within the concentration of 0.16–1.32 g/mmol Ti, Armostat 300 helps to increase the catalyst activity to 1.3–2 times. The variation of the titanium oxidation state of the catalyst in the presence of Armostat 300 at 80°C with Al/Ti molar ratio of 100 showed that Ti (III) species increased. The effect of Armostat 300 on T_m, % X_c, density, bulk density, and MFI of polymer was insignificant. In this work, Zonyl FSN‐100 with the formula R_f(CH₂CH₂O)_xH, R_f = F(CF₂CF₂)_y, y = 1–9, x = 1–26 was used as antifouling agent in copolymerization of ethylene with 1‐butene. It was found that Zonyl FSN‐100 at the concentration range of 5–20 ppm reduces the catalyst activity to 1.11–1.9 times. It was also shown that Ti (III) species in the presence of Zonyl FSN 100 decreased. This antifouling agent slightly decreased the properties of polymer including % X_c, density, and M_w. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 257–260, 2006     

Structure,processing, morphology,and property relationships of biaxially drawn Ziegler–Natta/metallocene isotactic polypropylene film

The structure, processing, morphology, and property relationships of biaxially drawn isotactic polypropylene (BOPP) film of mixed metallocene isotactic PP (m‐iPP) and Ziegler–Natta iPP (ZN‐iPP) homopolymer compositions are developed. The DSC and film drawing behavior show cocrystallization of the ZN‐iPP and m‐iPP components. The structure, processing, morphology, and property relations of ZN‐iPP/m‐iPP blends are compared with ZN‐iPP of varying isotacticities. The ZN‐iPP/m‐iPP blends exhibit reduced biaxial yield stress [σ_y(T)]. A fractional crystallinity model collapses the σ_y(T) data into a common normalized form over a range of draw temperatures, ZN‐iPP tacticities, and blend compositions. The simplified model is extended to define the interrelationships of yield activation and strain hardening behavior into regimes differentiated by characteristic draw stress (crystallinity) levels. Structure–property models are developed to explain the effect of draw temperature and resin–blend microstructure on the draw behavior, film stiffness, barrier, elongation, and synergies of the BOPP film processing–property balance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2400–2415, 2001     

Copolymerization of ethylene and propylene catalyzed by novel magnesium chloride supported,vanadium‐based catalysts

Two novel magnesium chloride supported, vanadium‐based Ziegler–Natta catalysts with 9,9‐bis(methoxymethyl)fluorene and di‐i‐butyl phthalate as internal donors were prepared and used in the copolymerization of ethylene and propylene. The catalytic behaviors of these catalysts were investigated and compared with those of traditional magnesium chloride supported, vanadium‐based catalysts without internal donors. Differential scanning calorimetry, gel permeation chromatography, and ¹³C‐NMR spectroscopy analysis were performed to characterize the melting temperatures, molecular weights, and molecular weight distributions as well as structures and compositions of the products. The copolymerization kinetic results indicated that the novel catalyst with 9,9‐bis(methoxymethyl)fluorene as an internal donor had the highest catalytic activity and optimal kinetic behavior in ethylene–propylene copolymerization with an ethylene/propylene molar ratio of 44/56. Low‐crystallinity and high‐molecular‐weight copolymers were obtained with these novel magnesium chloride supported, vanadium‐based catalysts. The reactivity ratio data indicated that the catalytic systems had a tendency to produce random ethylene–propylene copolymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

Study of propylene polymerization catalyzed by a spherical MgCl2‐supported Ziegler–Natta catalyst system: The effects of external donors

Spherical MgCl₂‐supported Ziegler–Natta catalysts containing internal donors, such as diethyl phthalate, diisobutyl phthalate, and di‐n‐octyl phthalate, have been prepared. The effects of external donors, phenyltrimethoxysilane, phenyltriethoxysilane, and diphenyldimethoxylsilane, on the propylene polymerization catalyzed by these catalysts were studied. The results indicate that the external donors not only led to an increase in the isotactic index, but also affected the morphology of resultant polymer particles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 738–742, 2005     

Preparation of novel MgCl2‐adduct supported spherical Ziegler–Natta catalyst for α‐olefin polymerization

In this article, preparation of novel MgCl₂‐adduct supported spherical Ziegler–Natta catalyst for α‐olefin polymerization is reported. The factors affecting the particle size (PS) and particle size distribution (PSD) of the prepared support were investigated. In this method, the internal donor added while preparing MgCl₂‐adduct support was supposed to act as a crosslinking agent. Therefore it provided a reasonable way to enhance the morphology and control the PS of the resultant polymer particles. The possible mechanism is discussed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 945–948, 2006