Isotacticity Index Research Articles

The Effect of Chain Tacticity on the Thermal Energy Parameters of Isotactic and Syndiotactic Polypropylene

The thermal energy properties in any material affect the substance’s capacity to store or transfer heat. This study investigated the effect of the polymeric chains’ tacticity on the thermal properties of polypropylene related directly to the thermal power, i.e., the heat capacity and thermal conductivity. The study selected different commercial polypropylene groups with two steric modes: isotactic and syndiotactic. The aim is to determine the parameters: isotacticity index, degree of crystallinity, glass-transition temperature, melting point, heat capacity, and thermal conductivity. The data were collected using gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC). The results showed that methyl groups randomly distributed within the homo-polypropylene changed the overall content of meso diads, i.e., less isotacticity index. The differences between isotactic and syndiotactic polypropylene groups were 20-40% the degree of the crystallinity, 5-10°C the glass-transition temperature, and 10-20°C the melting point. Using suitable mathematical models, these parameters can be related directly to specific heat capacity and thermal conductivity.

Ziegler-Natta catalyst particle size control in propylene/α-olefin (co)polymerizations

This study investigates the influence of particle size of Ziegler-Natta (ZN) catalysts on the micro-structure and properties of related polypropylenes. In this regard, three catalysts were synthesized with different particle sizes (PS) including PS < 25, 25 ≤ PS ≤ 45, and PS > 45 μm, but from the same ingredients. The catalyst characterization involved a wide range of methods including TGA, BET, SEM, EDS, XRD, LPS, and N2 adsorption-desorption techniques. Next, a series of propylene homopolymers and their copolymers with 1-hexene were prepared using the as-synthesized catalysts, in the presence or absence of H2 under similar reaction conditions. The synthesized (co)polymers were characterized with DSC, SSA, 13CNMR and TREF techniques. The activity was found to increase with decreasing catalyst particle size in both homo- and copolymerization experiments. Furthermore, a catalyst with a larger particle size provided a polymer with a lower isotacticity index, slightly longer meso sequence length, and higher 1-hexene content of about 10.57 %. This affirms the importance of catalyst/support particle size control during the preparation process in industrial polypropylene plants.

Influence of the Ethanol Content of Adduct on the Comonomer Incorporation of Related Ziegler-Natta Catalysts in Propylene (Co)polymerizations.

The aim of this work is to investigate the influence of the ethanol content of adducts on the catalytic behavior of related Ziegler-Natta (ZN) catalysts in propylene homo- and copolymerizations (with 1-hexene comonomer) in terms of activity, isotacticity, H2 response, and comonomer incorporation. For this purpose, three MgCl2.nEtOH adducts with n values of 0.7, 1.2, and 2.8 were synthesized and used in the synthesis of related ZN catalysts. The catalysts were thoroughly characterized using XRD, BET, SEM, EDX, N2 adsorption-desorption, and DFT techniques. Additionally, the microstructure of the synthesized (co)polymers was distinguished via DSC, SSA, and TREF techniques. Their activity was found to enhance with the adduct's ethanol content in both homo- and copolymerization experiments, and the increase was more pronounced in homopolymerization reactions in the absence of H2. Furthermore, the catalyst with the highest ethanol content provided a copolymer with a lower isotacticity index, a shorter meso sequence length, and a more uniform distribution of comonomer within the chains. These results were attributed to the higher total surface area and Ti content of the corresponding catalyst, as well as its lower average pore diameter, a larger proportion of large pores compared to the other two catalysts, and its spherical open bud morphology. It affirms the importance of catalyst/support ethanol-content control during the preparation process. Then, molecular simulation was employed to shed light on the iso-specificity of the polypropylene produced via synthesized catalysts.

Porous Organic Polymers-Supported Zeigler-Natta Catalysts for Preparing Highly Isotactic Polypropylene with Broad Molecular Weight Distribution.

Porous organic polymers (POPs) have attracted much attention in numerous areas, including catalysis, adsorption and separation. Herein, POP supported Ziegler-Natta catalysts were designed for preparation of isotactic polypropylene (iPP). The POPs-based Ziegler-Natta catalysts exhibited the characteristic of broad molecular weight distribution (MWD > 11) with or without adding an extra internal electron donor. The added internal electron donor 3-methyl-5-tert-butyl-1,2-phenylene dibenzoate (ID-2) used in cat-2 showed good propylene polymerization activity of 15.3 × 106 g·PP/mol·Ti·h, high stereoregularity with 98.2% of isotacticity index and broad molecular weight distribution (MWD) of 12.3. Compared to the MgCl2-supported Ziegler-Natta catalysts (cat-4) with the same ID-2, cat-2 showed higher chain stereoregularity for propylene polymerization. As seen in the TREF results, the elution peak of PP-2 (124.0 °C, 91.7%) is 1.5 °C higher than the isotactic fraction from PP-4 (122.5 °C, 87.2%), and even 1.2 °C higher than PP-5 prepared from ID-3 with the characteristics of high stereoregularity. Moreover, the pentad methyl sequence mmmm of PP-2 (93.0%) from cat-2 is 0.5% higher than that of PP-4 from cat-4. XPS analysis revealed that the minute difference in binding energy of Ti, Mg, C and O atoms exist between the inorganic MgCl2 and the organic polymer based Z-N catalysts. The plausible interaction mechanism of active sites of Mg and Ti with the functional groups in the POP support and the added ID was proposed, which could be explained by their high stereoregularity and the broad molecular weight distribution of the POP-based Z-N catalysts.

Effects of Prepolymerization, Temperature, and Hydrogen Concentration on Kinetics of Propylene Bulk Polymerization Using a Commercial Ziegler-Natta Catalyst

The effects of prepolymerization, temperature, and hydrogen concentration on propylene bulk polymerization with a commercial Ziegler-Natta catalyst were investigated, and the apparent polymerization rate constants were estimated by varying reaction temperatures, hydrogen partial pressures, and polymerization methods. It was shown that prepolymerization has different effects on the polymerization rate and isotacticity of the polymer; without prepolymerization, the polymerization rate and isotacticity reach their maximum at 70°C and 80°C, respectively, whereas the polymerization rate and isotacticity with prepolymerization increase with the polymerization temperature in the range of 50-80°C. Moderate prepolymerization time reduced the fine fraction while increasing polymerization rate and isotacticity. Appropriate prepolymerization technique can increase mass transfer performance and fragmentation, which is a promising way to improve polymerization rate, isotacticity index, and fine fraction. Otherwise, insufficient prepolymerization or excessive prepolymerization causes prepolymer particle fragmentation.

Sulfonated porous organic polymer supported Zeigler-Natta polypropylene catalysts with high stereoregularity and broad molecular weight distribution

Porous organic polymers (POPs) have received increasing attentions in a wide range of areas including adsorption, separation and catalysis. In this paper, a kind of sulfonated POP was designed, synthesized and used as Zeigler-Natta catalyst support for propylene polymerization. The prepared s-POP obtained highly porous structure with specific surface area of 542 m2/g (BET) and pore volume of 0.433 g/ml. The prepared s-POP based Zeigler-Natta catalysts with diisobutyl phthalate (ID-1) and 3-methyl-5-tert-butyl-1,2-phenylene dibenzoate (ID-2) exhibit good propylene polymerization activity, high stereoregularity and broad molecular weight distribution. The polymerization activity of Cat-2 with (ID-2) is 32.6 × 106 g.PP/mol.Ti. h with Mw/Mn of 13.8 and isotacticity index of 98.3%. The stereoregularity or isotactic sequence distribution of the prepared polypropylene (PP) was characterized by DSC、13CNMR and TREF techniques, and the results showed that the s-POP based catalyst (cat-2) with ID-2 obtained particularly higher isotatic sequence than the MgCl2-based Ziegler-Natta catalyst (cat-4) with the same internal donor. Pentad methyl sequence mmmm of PP-2 (94.1%) from cat-2 is 1.6% higher than that of PP-4 from cat-4, and the elution temperature of PP-2 (123.5 °C, 91%) is 1 °C higher than the isotactic fraction from PP-4 (122.5 °C, 87.2%). This characteristics of broad molecular weight and peculiar high stereoregularity of s-POP based catalyst could be attributed the modulation of chemical environment around Ti and Mg elements, and XPS analysis exhibited the minute difference of binding energy of Ti、Mg、C and O atoms. Furthermore, the plausible formation mechanism of active sites for the s-POP based Z-N catalyst was proposed.

Performance Evaluation of Polypropylene Resin for Capacitor Film

The molecular structure and mechanical properties of 3 kinds of imported polypropylene particles for capacitor film were analyzed by Gel Permeation Chromatograph (GPC), differential scanning calorimeter (DSC) and electronic tensile machine. The results showed that the melt index of imported polypropylene for capacitor film was about 3.0g/10min, the ash content was about 20ppm, the isotacticity index was higher than 98.5%, the crystallinity was higher than 45%, and the molecular weight distribution was wider than 6.0. The data showed these three kinds of imported polypropylene for capacitor film were all low-ash and higher isotactic polypropylene with high crystallinity and good mechanical tensile properties.

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

ABSTRACTThe 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.

POLYMERIZATION OF STYRENE USING ZIEGLER – NATTA CATALYST TYPE TICL4/MGCL2 – EB /ALET3

In this study Ziegler – Natta catalyst was prepared which is a multi component catalytic system composed of, titaniumtetrachloride (TiCl4) as a active material, anhydrous magnesium chloride MgCl2 as support (carrier) which distribute the active material, ethyl benzoate EB as electron donor compound, and triethylaluminum (AlEt3) as co-catalyst ( promoter ). This catalyst used to product stereoregular polystyrene with high percent of isotactic isomer. The effect of triethylaluminum concentration on polymer yield was also studied and found that optimum concentration of AlEt3 in the polymerization mixture is 0.257 M, The kinetic study showed that the rate of polymerization decay with time because of decrease in catalyst activity. The values of isotacticity index showed that the isotacticity decrease with increase triethylaluminum concentration

Functionalized multi-walled carbon nanotubes with stereospecific Ziegler-Natta catalyst species: Towards facile in situ preparation of polypropylene nanocomposites

Multi-walled carbon nanotubes (MWCNTs) were functionalized with a stereospecific Ziegler-Natta catalyst species for in situ preparation of polypropylene (PP)/MWCNT nanocomposites. The functionalization process involved initially treating MWCNTs containing a few (∼3.0% w/w) surface hydroxyl groups (MWCNT-OH) with an excess amount of Grignard reagent followed by further reaction with TiCl4. Triethylaluminum (TEA) and dimethoxydiphenylsilane (DDS) were used as co-catalyst and external electron donor, respectively. The resulting MWCNTs (MWCNT/Mg/Ti) only behaved as a fair isospecific Ziegler-Natta catalyst, promoting propylene polymerization at a moderate rate and resulting in PP with moderate isotacticity indices (76.4–91.0%). To improve the catalytic performance, the electron-donating reagent 9,9-bis(methoxymethyl)fluorine (BMMF) was added into the MWCNT functionalization process, incorporating BMMF into the catalytic material and simultaneously reducing the quantity of TiCl4 immobilization. The BMMF-incorporated functionalized MWCNTs (MWCNT/Mg/BMMF/Ti) produced PP with a high isotacticity index (92.0%) without the use of an external electron donor. PP with an isotacticity index greater than 98% was achieved when DDS was used as external electron donor during the polymerization process.

Fourier transform infrared spectroscopy and wide‐angle X‐ray scattering: Investigations on polypropylene–vapor‐grown carbon nanofiber composites

AbstractFourier transform infrared (FTIR) spectroscopy and wide‐angle X‐ray scattering (WAXS) investigations of isotactic polypropylene (iPP)–vapor‐grown carbon nanofiber (VGCNF) composites containing various amounts of VGCNFs ranging between 0 and 20 wt %. are reported. The FTIR investigations were focused on the regularity bands of iPP. The FTIR data indicated a drop in the isotacticity index as the concentration of nanofibers was increased; this suggested a decrease in the crystallinity. WAXS measurements revealed a dominating α1 phase, with a small admixture of γ phase or mesophase. The loading of the polymeric matrix with carbon nanofibers (CNFs) did not induce significant changes in the morphology of the polymeric matrix. A weak decrease in the size of α crystallites upon loading of CNFs was noticed. The experimental data obtained by FTIR spectroscopy supported the WAXS data. Spectroscopic data (a drop in the isotacticity index as estimated by FTIR spectroscopy and the ratio between the crystalline and total areas of WAXS lines assigned to iPP) failed to confirm the enhancement of the degree of crystallinity of polypropylene upon loading by nanofibers. However, whereas both techniques can identify with a high accuracy vibrations in ordered domains (FTIR spectroscopy) and the crystalline structure, including the lattice parameters and the size of crystallites (WAXS), difficulties in the correct assessment of the baseline and of amorphous components may result in important errors (typically &gt;5%) in the estimation of the degree of crystallinity of the polymeric component. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Influences of silane/ether composite external donors on propylene polymerization with MgCl2-supported Ziegler-Natta catalyst in the presence of hydrogen

AbstractIn this work, the effects of two silane type external donors, Ph2Si(OCH3)2 (DPDMS) and dicyclopentyldimethoxysilane (DCPDMS) on propylene slurry polymerization in the presence of hydrogen with a MgCl2/TiCl4/DIBP - Al(C2H5)3 catalyst system were investigated, and the tacticity distribution and molecular weight distribution (MWD) of polypropylene (PP) were further regulated by using silane/ether (ROCH3, R = n-Bu, i-C8H17) composite external donors. The tacticity distribution of PP, as revealed by successive self-nucleation and annealing (SSA) thermo analysis of the polymer, is markedly changed by the external donors. DCPDMS shows much stronger effects than DPDMS. Addition of the ether as an auxiliary external donor in MgCl2/TiCl4/DIBP-TEA/silane (DPDMS or DCPDMS) lead to further increase in catalytic activity and isotacticity of PP, and changes in tacticity distribution. By using the composite external donors, PP with both higher isotacticity index, lower molecular weight or narrower molecular weight distribution was prepared at high activity. Effects of the external donors on the active center distribution were discussed based on the results of deconvoluting the MWD curve with multiple Flory “most-probable” distributions, and possible mechanism of the external donor effects was proposed.

Polydentate phosphine oxides as external electron donors for titanium-magnesium catalysts for propylene polymerization

The possibility of using R n P(O)(CH2OR′)3—n (R = alkyl, R′ = methyl or acyl, n = 0–2) polydentate phosphine oxides as external electron donors for the titanium-magnesium catalysts for isotactic polypropylene synthesis is demonstrated for the first time. The kinetics of propylene polymerization in liquid monomer at 70°C and the isotacticity and molecular-weight characteristics of the resulting polypropylene are studied as functions of the nature of the substituents at the phosphorus atoms in the external donor and the molar ratio of the cocatalyst AlEt3 to the external electron donor. Among the compounds examined, isoamyldi(methoxymethyl)phosphine oxide (R = iso-Am, R′ = Me, n = 1) is the most efficient. The isotacticity index of the polypropylene (PP) synthesized on the titanium-magnesium catalyst with this external donor is as high as 94–95%, and the activity of the catalyst (Cat) in the absence of hydrogen is 5.0–6.5 (kg PP) (g Cat)−1 h−1. With the optimum combination, the activity of this catalyst is ≈5 (kg PP) (g Cat)−1 h−1 and the isotacticity index is 94%. These parameters are close to those obtained for propylene polymerization in the absence of hydrogen on the same titanium-magnesium catalyst with phenyltriethoxysilane (external donor used in the industrial synthesis of PP): the activity is 5.6 (kg PP) (g Cat)−1 h−1, and the isotacticity index is 95%. The introduction of hydrogen into the reaction zone makes it possible to efficiently control the molecular weight of PP, increases the catalyst activity by a factor of 1.5–2.5, and somewhat decreases the isotacticity index (from 94 to 91–92%).

Modeling and Simulation of Olefin Polymerization at Microstructure level

A new model based on a combination of the polymeric multigrain and multilayer models has been developed to predict the polymerization rate, particle growth, morphology, effective parameters on broadening of the molecular weight distribution, number and weight average of the molecular weight, isotacticity index and bulk density of polymer. Mathematical correlations and the kinetics used in this model are based on the polymeric multigrain and the multilayer models, respectively. In the modeling, multiplicity of active site using different kinetics parameters as well as deactivation of catalyst during the polymerization have been considered,. Moreover, it considers mass transfer effects on polymerizatio n characteristic s. The Effects of physico-chemical aspects of catalyst associated with the polymerization in slurry phase are also considered in this model. In addition, the effects of more important model parameters including time step, number of layers and number of active sites on the produced polymer features are reviewed. The model predictions show that propagation rate constant, multiplicity of active site, concentration of any individual active site type, and the initial size of the catalyst particles have considerable effects on the properties of the final polymer. The results obtained from simulation with this new combined model confirm at least better qualitative prediction of the polymerization characteristics in comparison with simulation results of the multigrain model (MGM) and the two models mentioned above.

Comparative study of propylene polymerization using monosupported and bisupported titanium‐based Ziegler–Natta catalysts

AbstractHeterogeneous Ziegler–Natta systems—MgCl2 (ethoxide type)/TiCl4/di‐n‐butyl phthalate (DNBP)/triethylaluminum (TEA)/dimethoxymethylcyclohexylsilane (DMMCHS) and SiO2/MgCl2 (ethoxide type)/TiCl4/DNBP/TEA/DMMCHS—were studied for the polymerization of propylene. The slurry polymerization of propylene was carried out with the catalyst systems in n‐heptane. Both systems performed with optimum activity at a particular [Al]/[DMMCHS]/[Ti] molar ratio. The ratio to reach the highest activity was much lower for the bisupported catalyst system. The productivity of the bisupported catalyst was higher than that of the monosupported one. Polypropylene of a high isotacticity index (II; &gt;96%) was obtained with both systems and did not significantly change with an increasing [Al]/[DMMCHS]/[Ti] molar ratio. The addition of hydrogen as a chain‐transfer agent reduced II of the polymers obtained with both systems. The effect of the polymerization temperature (40–75°C) on the viscosity‐average molecular weight (Mv) and II showed a decrease in both cases. The bisupported catalyst system produced a polymer with higher Mv. The effect of temperature on II was similar for both the monosupported and bisupported systems. A monomer pressure of 2.02 × 105 to 0.8 × 106 Pa increased Mv of the obtained polymer. II of the polymer slightly decreased with increasing monomer pressure. The titanium content of the catalyst was 1.70 and 3.55% for the monosupported and bisupported systems, respectively. The surface area of the bisupported catalyst was higher than that of the monosupported catalyst. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2220–2226, 2006

Polymerization of propylene using MgCl2 (ethoxide type)/TiCl4/diether heterogeneous Ziegler–Natta catalyst

AbstractHeterogeneous Ziegler–Natta catalyst of MgCl2 (ethoxide type)/TiCl4/diether was prepared. 2,2‐Diisobutyl‐1,3‐dimethoxy propane (DiBDMP), diether, was used as internal donor. Slurry polymerization of propylene was carried out using the catalyst in dry heptane while triethylaluminium (TEA) was used as co‐catalyst. The co‐catalyst effects, such as catalyst molar ratio, polymerization temperature, H2 pressure, external donor, triisobutylaluminium (TiBA) and monomer pressure, on the activity of the catalyst and isotacticity index (II) of the polymers obtained were studied. Rate of polymerization versus polymerization time is of a decay type with no acceleration period. There are an optimum Al/Ti molar ratio and temperature to obtain the highest activity of the catalyst. The maximum activity was obtained at 60 °C. Increasing the monomer pressure to 1 010 000 Pa linearly increased the activity of the catalyst. Addition of hydrogen to 151 500 Pa pressure increased activity of the catalyst from 2.25 to 5.45 kg polypropylene (PP) (g cat)−1 h−1 using 505 000 Pa pressure of monomer. The II decreased with increasing Al/Ti ratio, monomer pressure, hydrogen pressure and increased with increasing temperature to 60 °C, following with decrease as the temperature increases. Productivity of 11.55 kg (PP) (g cat)−1 h−1 was obtained at 1 010 000 Pa pressure of monomer and temperature of 60 °C. Addition of methyl p‐toluate (MPT) and dimethoxymethyl cyclohexyl silane (DMMCHS) as external donors decreased the activity of the catalyst sharply, while the II slightly increased. Some studies of the catalyst structure and morphology of the polymer were carried out using FTIR, X‐ray fluorescence, scanning electron microscopy and Brunauer–Emmett–Teller techniques. Copyright © 2005 Society of Chemical Industry

C2- and Cs-symmetric diamidodichlorotitanium complexes: Syntheses, structures and 1-hexene polymerization catalysis

The complexes l-[CMe 2{CHMeN(2-Pr i -C 6H 4)} 2TiCl 2] ( 2) and u - [ CMe 2 { CHMeN ( 2 , 6 - Pr 2 i C 6 H 3 ) } 2 TiCl 2 ] ( 3), C 2- and C s -symmetric analogues, respectively, of McConville’s C 2 v hexene polymerization precatalyst [ ( CH 2 ) 3 { N ( 2 , 6 - Pr 2 i – C 6 H 3 ) } 2 TiCl 2 ] ( 1), were prepared by high-dilution salt-elimination from the lithium amides and characterized spectroscopically and crystallographically. Complex 2, though less active than 1, was a highly active catalyst of polymerization of 1-hexene when activated by MAO. Complex 3 was inactive under similar conditions. NMR analysis confirmed that there were more mmmm pentads in polymer produced by 2 than in the statistically atactic material produced by 1, though the isotacticity index was not high. The results are interpreted in terms of an isotactic/atactic block structure, caused by syn/ anti fluxion of the two 2-isopropylphenyl rings in 2. Kinetic profiles and polydispersities were consistent with a slow initiation step involving monomer, followed by rapid propagation, with some chain transfer to aluminium and only a small extent of β-hydride elimination. The rubber-like polymers were indistinguishable by thermal analysis from those prepared by Ziegler–Natta catalyst systems.

Badania kopolimeryzacji propylenu z etylenem

Propylene/ethylene copolymers (EPR) containing up to 4 molar % of ethylene were prepared in the presence of supported titanium-magnesium catalyst TiCl 4 /MgCl 2 activated with dibutyl phthalate as internal donor, AlEt 3 ascocatalyst and dicyclopentylodimethoxysilane as external donor. The process of one-stage suspension copolymerization has been carried out. The effects of copolymerization time, initial ethylene content in the reaction mixture (c E t ), temperature and pressure on the catalytic system activity and copolymerization rate (R p ) were studied (Figs. 1 and 2, Table 1). Ethylene content in EPR and its weight average molecular weight (M w ) as time functions were also analyzed (Figs. 3 and 4). The results show that using of highly active titanium catalyst let obtain higher yield of copolymers containing up to 4 molar % of ethylene, in comparison with the yield of propylene homopolymer. However, an increase in ethylene content in EPR causes increase in atactic propylene fraction content and decrease in isotacticity index (II) as well as in bulk density (Table 1). Tensile properties and freeze resistance (impact strength at low temperature) of selected EPR samples have been determined and compared with respective properties of propylene homopolymer and of copolymer prepared earlier in two-stage process (Table 2). Copolymers, especially those produced in two-stage process, show improved strength properties, particularly better freeze resistance.

Microstructural characteristics and thermal properties of ansa‐zirconocene catalyzed copolymers of propene with higher α‐olefins

AbstractCopolymers of propene and several higher α‐olefins, 1‐butene, 1‐pentene, 1‐hexene, 1‐heptene, 1‐octene, and 4‐methyl‐1‐pentene (4M1P), have been prepared with two different metallocene catalysts, rac‐Et(Ind)2ZrCl2 (EI) and rac‐Me2Si(2‐MeBenz‐[e]Ind)2ZrCl2 (MBI), and comprehensively characterized by 13C NMR spectroscopy. All copolymers produced with EI have comparable isotacticities as well as similar stereosequences. The copolymers produced with MBI significantly differ both from the reference propene homopolymer and among themselves: in fact, they are characterized by rather low isotacticities and the degree of tacticity is strongly influenced by comonomer type and concentration. A detailed 13C NMR analysis revealed that these copolymers are constituted by highly isotactic and atactic sequences of various lengths. The similar thermal behavior, in terms of transition temperatures, for the homologues of the series obtained with the two different catalysts show that the capability of crystallization of these systems is not directly connected to the overall microstructural properties (e.g. the isotacticity index) but can be accounted for by the details of the microstructure.

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

AbstractThe 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