Though preparation procedures of heterogeneous Ziegler‐Natta catalysts for propylene polymerization are sophisticated, it is uncertain whether the nature of the active sites is similar or different for different preparation procedures. In this study, the effects of preparation procedures on the nature of the active sites were investigated by stopped‐flow polymerization in combination with microstructure analysis of polymers. Both basic and advanced types of catalysts showed the same two kinds of isospecific active site, which indicated little influence of the preparation method on the active site structure. On the contrary, the ratios of the two kinds of isospecific sites were not the same, resulting in variation of average polymer properties.
Results of propene polymerization in the presence of two known octahedral C2‐symmetric Zr complexes bearing tetradentate [ONNO]‐type ligands are reported for the first time. Depending on the steric hindrance at the active metal, isotactic site‐controlled or weakly syndiotactic chain‐end‐controlled polymers were obtained, in both cases via highly regioselective 1,2 (primary) monomer insertion. In this respect, the complexes mimic the behavior of the active Ti species on the surface of the heterogeneous Ziegler‐Natta catalysts of which they might represent good structural models. 相似文献
In this study, novel carrier materials were synthesized by addition of metal dihalide compounds in the synthesis reaction of magnesium diethoxide using metallic magnesium, ethanol and iodine. Poly(propylene) polymerizations were then investigated with the MgCl2‐supported TiCl4 catalysts using these carrier materials. As results, magnesium diethoxide with extremely large particle sizes and spherical shapes were obtained and the angles of repose of PP particles obtained by using their catalysts as a flowability index showed high values. Furthermore, in order to confirm key points for excellent catalyst performance from detailed characterizations, SEM images, compositions and WAXS were measured.
Experiments designed to prepare Ziegler‐Natta catalysts with controlled particle morphology are reported. Different dealcoholation processes are used on the adduct MgCl2 · nEtOH to prepare the catalysts: either thermal treatment or chemical dealcoholation employing different substances such as titanium tetrachloride, triethylaluminium, dichlorodimethylsilane, and chlorotrimethylsilane. In addition, dichlorodimethylsilane dealcoholation is also performed after thermal treatment. SEM analysis of adducts, supports, and catalysts is carried out. The obtained catalysts are characterized through impregnated titanium content evaluation. The polyethylenes and poly(propylene)s obtained employing the so prepared catalysts show spherical morphology when examined by optical microscopy.
A Ziegler‐Natta/metallocene hybrid catalyst was produced and utilized in the polymerization of ethylene with the aim of producing bimodal polyethylene. The MgCl2 adduct was prepared by a melt quenching method and Cp2ZrCl2 and TiCl4 catalysts were loaded, respectively, after treating the surface with TiBAl. The polymerization kinetics involved an induction period, followed by fragmentation and expansion of particles. SEM micrographs revealed that the spherical morphology was retained through the initial mild reaction conditions of induction period. The polymers produced showed bimodal molecular weight distribution patterns, suggesting that both components of the hybrid catalyst were active over the support.
Two different modeling techniques, the method of moments and Monte Carlo simulation, were compared for propylene polymerization with coordination catalysts including a new mechanistic step, site transformation by electron donors. We used the models to show how the molecular weight and tacticity distributions of several poly(propylene) chain populations were affected by changing the concentration of hydrogen, electron donor, and propylene in the reactor, under steady‐state or dynamic operating conditions. The Monte Carlo simulation describes the molecular weight and tacticity distributions for the whole polymer and chain populations with distinct microstructural characteristics. We have also applied the Monte Carlo model to simulate the pentad sequence distributions and its equivalent 13C NMR spectra.
Deconvolution of the MWD of a polymer produced by multi‐site catalysts into independent Flory modes is the first step in modeling the polymerization process. A new deconvolution procedure for GPC data is developed that does not require an a priori assumption concerning the nature of the discrete distribution and can be used with a continuous distribution. The MWD measured via GPC is a linear function of the individual catalytic sites, but it is numerically ill‐conditioned, preventing direct inversion of the GPC data. Tikhonov regularization has been developed to uniquely invert the MWD. Applying the regularizing method to a polyethylene produced via a Ziegler‐Natta catalyst, seven discrete sites were found, and the kinetic constant ratios were determined for each of these sites.
In propylene polymerization with MgCl2‐supported Ziegler‐Natta catalysts, it is known that the reduction of TiCl4 with alkylaluminum generates Ti3+ active species, and at the same time, leads to the growth of TiClx aggregates. In this study, the aggregation states of the Ti species were controlled by altering the Ti content in a TiCl3/MgCl2 model catalyst prepared from a TiCl3 · 3C5H5N complex. It is discovered that all the Ti species become isolated mononuclear with a highly aspecific feature below 0.1 wt.‐% of the Ti content, and that the isolated aspecific Ti species are more efficiently converted into highly isospecific ones by the addition of donors than active sites in aggregated Ti species.