Polymer support of “single-site” catalysts for heterogeneous olefin polymerization

Covalent Organic Framework-Supported Metallocene for Ethylene Polymerization

The loading of homogeneous catalysts with support can dramatically improve their performance in olefin polymerization. However, the challenge lies in the development of supported catalysts with well-defined pore structures and good compatibility to achieve high catalytic activity and product performance. Herein, we report the use of an emergent class of porous material-covalent organic framework material (COF) as a carrier to support metallocene catalyst-Cp2 ZrCl2 for ethylene polymerization. The COF-supported catalyst demonstrates a higher catalytic activity of 31.1×106  g mol-1  h-1 at 140 °C, compared with 11.2×106  g mol-1  h-1 for the homogenous one. The resulting polyethylene (PE) products possess higher weight-average molecular weight (Mw ) and narrower molecular weight distribution (Ð) after COF supporting, that is, Mw increases from 160 to 308 kDa and Ð drops from 3.3 to 2.2. The melting point (Tm ) is also increased by up to 5.2 °C. Moreover, the PE product possesses a characteristic filamentous microstructure and demonstrates an increased tensile strength from 19.0 to 30.7 MPa and elongation at break from 350 to 1400 % after catalyst loading. We believe that the use of COF carriers will facilitate the future development of supported catalysts for highly efficient olefin polymerization and high-performance polyolefins.

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.

Sidechain Metallopolymers with Precisely Controlled Structures: Synthesis and Application in Catalysis

Inspired by the cooperative multi-metallic activation in metalloenzyme catalysis, artificial enzymes as multi-metallic catalysts have been developed for improved kinetics and higher selectivity. Previous models about multi-metallic catalysts, such as cross-linked polymer-supported catalysts, failed to precisely control the number and location of their active sites, leading to low activity and selectivity. In recent years, metallopolymers with metals in the sidechain, also named as sidechain metallopolymers (SMPs), have attracted much attention because of their combination of the catalytic, magnetic, and electronic properties of metals with desirable mechanical and processing properties of polymeric backbones. Living and controlled polymerization techniques provide access to SMPs with precisely controlled structures, for example, controlled degree of polymerization (DP) and molecular weight dispersity (Đ), which may have excellent performance as multi-metallic catalysts in a variety of catalytic reactions. This review will cover the recent advances about SMPs, especially on their synthesis and application in catalysis. These tailor-made SMPs with metallic catalytic centers can precisely control the number and location of their active sites, exhibiting high catalytic efficiency.

Ionic Liquid-Modified Porous Organic Polymers as Efficient Metallocene Catalyst Supports

Porous organic polymers (POPs) are widely used in various areas such as adsorption, separation and catalysis. In the present work, ionic liquid-modified porous organic polymers (IL-POPs) synthesized by dispersion polymerization were applied to immobilize metallocene catalysts for olefin polymerization. The prepared IL-POPs were characterized by Fourier transform infrared spectrometer (FT-IR), nitrogen sorption porosimetry, X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), inductively coupled plasma atomic emission spectrometer (ICP) and scanning electron microscope (SEM) analysis. The IL-POPs obtained pores with surface specific area (SSA) ranging from 16.9 m2/g to 561.8 m2/g, and total pore volume (TPV) ranging from 0.08 cm3/g to 0.71 cm3/g. The supported catalysts Zr/MAO@IL-POPs exhibit great activity (3700 kg PE/mol·Zr·bar·h) in ethylene polymerization, and the GPC-IR results show that the polyethylene has narrow molecular weight distribution (2.2 to 2.8). The DSC results show that the melting point of prepared polyethylene was as high as 138 °C, and the TREF analysis results indicate that they have similar chemical composition distribution with elution temperature at 100.5–100.7 °C.

Hydrophilic Polysiloxane Microspheres and Ceramic SiOC Microspheres Derived from Them

In this overview article, the research on polysiloxane microspheres performed in the authors’ laboratory is briefly reviewed. These microspheres are prepared in water emulsion from polyhydromethylsiloxane (PHMS). This polymer is cross-linked in the emulsion process by hydrosilylation using various low molecular weight cross-linkers having at least two vinyl functions. The microspheres contain a large number of silanol groups which give them hydrophilicity and a broad possibility of functionalization by condensation with reactive silanes bearing a functional group in the organic radical. Further transformation of these functions leads to materials for practical use, such as catalysts and biocidal powders. The hydrophilic-hydrophobic properties of the microspheres may be fine-tuned by silylation or modification of the precursor PHMS polymer. Pristine microspheres are highly hydrophilic and well-dispersed in water. They do not adsorb proteins and hydrophobic organic substances. Macropores may be generated in these particles by a simple modification of the emulsion procedure. These microspheres are also very good precursors for ceramic silicon oxycarbide microsphers because they retain their shape in pyrolytic processes even at high temperatures; and they give a high yield of ceramic material. The polysiloxane microspheres heated at 600 °C give micro and mezo porous materials with specific surface above 500 m2/g. When pyrolysed at temperatures 1000–1400 °C, they form solid ceramic microspheres of high strength. They retain spherical shape at 1500 °C although cracks are formed at their surfaces. Etching them with HF(aq) solution gives porous microspheres with specific surface above 1000 m2/g that is almost devoid of SiO2.

Advances in Mathematical Modeling of Gas-Phase Olefin Polymerization

Mathematical modeling of olefin polymerization processes has advanced significantly, driven by factors such as the need for higher-quality end products and more environmentally-friendly processes. The modeling studies have had a wide scope, from reactant and catalyst characterization and polymer synthesis to model validation with plant data. This article reviews mathematical models developed for olefin polymerization processes. Coordination and free-radical mechanisms occurring in different types of reactors, such as fluidized bed reactor (FBR), horizontal-stirred-bed reactor (HSBR), vertical-stirred-bed reactor (VSBR), and tubular reactor are reviewed. A guideline for the development of mathematical models of gas-phase olefin polymerization processes is presented.

Ethylene polymerization with a nickel diimine catalyst covalently anchored on spherical ZSM-5

Late transition catalysts play an important role in the catalytic conversion of olefins into polymers with different microstructures.

GAS-PHASE POLYMERIZATION OF 1,3-BUTADIENE WITH PS-DVB–SUPPORTED RARE EARTH CATALYST AND AN INVESTIGATION ON EFFECTS OF DISPERSANTS

Organic supporter poly(styrene-co-divinylbenzene) (PS-DVB) was synthesized, and gas-phase polymerization of 1,3-butadiene was performed with PS-DVB–supported Nd(vers)3/Al2Et3Cl3/Al(i-Bu)3 catalysts. Millimeter-sized granules of high cis-1,4 content (>98%) polybutadiene with an Mn of 5.3–5.5 × 105 were obtained. Dispersants used in gas-phase polymerization of 1,3-butadiene have a significant influence on apparent activities of catalysts and appearance of products. The morphology of polybutadiene granules was also investigated by scanning electron microscopy.

Metal oxide as a template in the preparation of porous poly(2-hydroxyethylmethylacrylate-co-divinylbenzene) particles as a metallocene catalyst support

Porous functional P(HEMA-co-DVB) particles with controllable pore structure and morphology were prepared using metal oxide as particle-forming template.

Synthesis and characterization of functional porous organic polymers as efficient metallocene catalyst supports

Porous P(HEMA-co-DVB) particles with tunable pore structure and morphology were prepared by a dispersion polymerization strategy.

Preparation of uniform poly(urea–siloxane) microspheres through precipitation polymerization

Preparation of PUSs through precipitation polymerization.

Surface coordination polymerization of ethylene by hydrozirconation-immobilized metallocene

Hydrozirconation on vinyl-terminated substrates (silicon wafer and nanosilica sphere) is employed as an efficient way for immobilization of zirconocene catalyst through Zr-C bonds, which is applied in surface coordination ethylene polymerization producing surface-tethered polyethylene (PE). The formation of Zr-C σ bond induced by hydrozirconation provides an initiator precursor for growing a layer of PE covalently linked onto substrates. The results from SEM, AFM, and TEM show that the surface polymerization is controlled by hydrozirconation. Surface pattern or core-shell structure with crystalline PE coating can be formed, when silicon wafer is selectively functionalized with vinyl-groups or vinyl-modified nanosilica is applied. It is believed that hydrozirconation for the synthesis of zirconocene initiator can be a versatile route to prepare polyolefin hybrid materials.