Internal Electron Donor Research Articles

The Effects of Internal Electron Donors on MgCl2-Supported Ziegler–Natta Catalysts for Isotactic PP

The electron donors (ED) in Ziegler–Natta (Z-N) catalysis are classified as internal electron donors (IED) and external electron donors (EED), and both IED and EED are indispensable components for enhancing the catalytic reactivity and regulating the stereoregularity of polyolefinic materials in a typical industrial Z-N catalytic process. With the intensive research on ED, the Z-N catalyst performances have experienced successive progress in the last few decades. Polypropylenes (PP) as a commodity polyolefin material, especially the isotactic PP (iPP), are produced in multi-billion pounds per annum by utilization of the various IED- and EED-assisted Z-N catalysts systems. In the course of developing Z-N catalysts, the ED constitutes a key component of the content and represents a significant area of future research. In this review, we introduced a concise overview of the functions of IEDs in the generations of Z-N catalyst systems and the widely used IED types (A total of 11 different types of IEDs are encompassed within this study) that have been developed so far. In addition, we focused on the coordination modes of different IEDs in the MgCl2-supported Z-N catalyst system and analyzed the effects of different types of IEDs on the PP isotacticity, regioselectivity, hydrogen sensitivity, and briefly introduced the application of environmentally friendly rosinate and salicylate IEDs.

Probing ligands to reaction centers to limit the photocycle in photosynthetic bacterium Rubrivivax gelatinosus

Light-induced electron flow between reaction center and cytochrome bc1 complexes is mediated by quinones and electron donors in purple photosynthetic bacteria. Upon high-intensity excitation, the contribution of the cytochrome bc1 complex is limited kinetically and the electron supply should be provided by the pool of reduced electron donors. The kinetic limitation of electron shuttle between reaction center and cytochrome bc1 complex and its consequences on the photocycle were studied by tracking the redox changes of the primary electron donor (BChl dimer) via absorption change and the opening of the closed reaction center via relaxation of the bacteriochlorophyll fluorescence in intact cells of wild type and pufC mutant strains of Rubrivivax gelatinosus. The results were simulated by a minimum model of reversible binding of different ligands (internal and external electron donors and inhibitors) to donor and acceptor sides of the reaction center. The calculated binding and kinetic parameters revealed that control of the rate of the photocycle is primarily due to 1) the light intensity, 2) the size and redox state of the donor pool, and 3) the unbinding rates of the oxidized donor and inhibitor from the reaction center. The similar kinetics of strains WT and pufC lacking the tetraheme cytochrome subunit attached to the reaction center raise the issue of the physiological importance of this subunit discussed from different points of view. SignificanceA crucial factor for the efficacy of electron donors in photosynthetic photocycle is not just the substantial size of the pool and large binding affinity (small dissociation constant KD = koff/kon) to the RC, but also the mean residence time (koff)−1 in the binding pocket. This is an important parameter that regulates the time of re-activation of the RC during multiple turnovers. The determination of koff has proven challenging and was performed by simulation of widespread experimental data on the kinetics of P+ and relaxation of fluorescence. This work is a step towards better understanding the complex pathways of electron transfer in proteins and simulation-based design of more effective electron transfer components in natural and artificial systems.

Internal Electron Donor Accelerated Sulfur Redox for Aqueous Zn─S Batteries

AbstractImproving the electrical conductivity of sulfur cathode while ensuring its high affinity to catalyst holds the key to facilitate the reaction kinetics of aqueous zinc–sulfur batteries. Herein, the sulfur redox in aqueous electrolyte is accelerated by introducing selenium–sulfur bonds into the sulfur structure to build an internal electron transport path. The Se with less electronegativity can act as an electron donor to accelerate the binding between S and Zn2+. Meanwhile, the bonded Se in the electron‐poor state endows the modified sulfur cathode with a strong affinity to the I3− catalyst, which further facilitates the conversion efficiency. Thus, the internal electron donor assisted sulfur cathode delivers excellent electrochemical performance in terms of high reversible capacity (1490 mAh g−1 at 0.5 A g−1), competitive rate performance (1010 mAh g−1 at 4 A g−1), as well as outstanding cycle stability (735 mAh g−1 at 4 A g−1 after 500 cycles).

Experimental and Theoretical Insights into the Effect of Dioldibenzoate Isomers on the Performance of Polypropylene Catalysts.

Experimental investigations and density functional theory (DFT) calculations were carried out to study the comprehensive effect of different 3,5-heptanedioldibenzoate (HDDB) optical isomers as the internal electron donor on the catalytic performance of Ziegler-Natta catalysts. The experimental catalytic activity of HDDB has a positive correlation with the relative content of the mesomer incorporated during catalyst preparation, while the hydrogen response of HDDB displayed a negative correlation with the relative content of the mesomer. In order to apply the DFT calculation results to the macroscopic activity of the catalyst, the content of the active centers of the catalyst was analyzed. Assuming that the content of the active centers is proportional to the internal electron donor content of the catalyst, binary linear regression was carried out, which showed a good linear correlation between experimental activity data and internal electron donor content. Furthermore, the fitted activity of the single active centers aligned well with the calculated activation energies. These results revealed that the catalytic activity of polypropylene (PP) catalysts is dependent on both the active center content and the catalytic activity of an individual active center. Additionally, the lower hydrogen response of HDDB leads to a higher molecular weight of polypropylene obtained from the RS-containing catalyst compared to the SS-containing catalyst. Further study reveals that the hydrogen transfer reactions of 2,4-pentanediol dibenzoate (PDDB)/HDDB are influenced by the orientation of the methyl/ethyl groups in different isomers, which affect the activation energy differences between the hydrogen transfer reaction and the propylene insertion reaction, and finally influence the molecular weight of PP.

Effect of internal and external electron donors on stereospecific polymerization of isoprene with TiCl4/MgCl2 type Ziegler-Natta catalysts

Two TiCl4/MgCl2 type Ziegler-Natta catalysts containing ethyl benzoate (EB) and dibutyl phthalate (DBP) as internal electron donors (ID) were prepared for isoprene polymerizations using five kinds of external electron donors (ED) (phenyltrimethoxysilane (ED-1), dicyclopentyl(dimethoxy)silane (ED-2), 2-butyl-2-ethyl-1,3-dimethoxypropane (ED-3), 1,3-dimethoxypropane (ED-4) and di(2-ethylhexyl)phthalate (ED-5)). The structure features of TiCl4/ID/MgCl2 catalysts were characterized and the effect of ID and ED on polymerization behaviors was studied. EB had higher adsorption content on catalyst surface, higher catalytic activity and lower trans-1,4 stereoselectivity than DBP. Appropriate introduction of ED-1 and ED-2, expect ED-3, ED-4 and ED-5, caused the enhancement in polymerization activity and trans-1,4 content, while excess addition led to the deactivation. The effect of ED on equilibrium between selective activation and deactivation of active species significantly relied on the electron donor type and concentration.

Visible-Light-Responsive Photoreversible Multi-Color Switching for Rewritable Light-Printing and Information Display.

Photoreversible color switching systems (PCSSs) exhibiting multi-color responses to visible light are favored for sustainable societal development over those relying on ultraviolet light due to safer operation and better penetration depth. Here, a PCSS capable of multi-color switching responsive to visible light based on highly photoreductive rutile-phase Sn-doped TiO2-x nanoparticles is reported. The Sn-doping significantly red-shifts the absorption band of the nanoparticles to the visible region, improving charge separation and transfer efficiencies and introducing Ti3+ species and oxygen vacancies as internal sacrificial electron donors for scavenging photogenerated holes. The resulting Sn-doped TiO2-x nanoparticles feature exceptional photoreduction ability and activity, thereby enabling photoreversible color switching of various redox dyes operational under visible light illumination. Furthermore, multi-color switching can be achieved via the color overlay effect by combining different redox dyes in one system, opening the door to many advanced applications, as demonstrated in their successful uses for developing visible-light-driven rewritable multi-color light-printing systems and visual information displays.

Effects of Internal Electron Donor on Distribution and Reactivity of Active Centers in Ethylene/1‐Hexene Copolymerization with MgCl2‐Supported Ziegler‐Natta Catalyst

AbstractEthylene/1‐hexene copolymerization with two MgCl2‐supported Ziegler‐Natta catalysts containing no internal electron donor or diethylphthalate (DEP) is conducted for different polymerization time . Effects of DEP on active center distribution are studied by fractionating each copolymer sample into boiling n‐heptane soluble (C7‐sol) and insoluble (C7‐ins) fractions, and counting the number of active centers in the copolymer fractions . The main effect of introducing DEP in the catalyst are reduction in the Ti content and significant increase in the proportion of active centers producing C7‐ins fraction. The propagation rate constants of ethylene insertion (kpE) and 1‐hexene insertion (kpH) are respectively estimated by linear fitting/extrapolating the change of apparent propagation rate constants (kpi)a with polymer yield according to a simplified multi‐grain particle model. In both catalysts, kpE in the C7‐ins fraction is 9–12 times larger than that in the C7‐sol fraction, and kpH in the C7‐ins fraction is 3–4 times larger than that in the C7‐sol fraction. The two groups of active centers have distinctly different catalytic properties. Introducing DEP reduced the kpE and kpH values and the extent of diffusion limitation . In summary, addition of electron donor in MgCl2‐supported Z‐N catalyst significantly changed the active center distribution and catalytic properties of its two groups of active centers.

Influence of the synthetic procedure on the properties of three Ziegler-Natta catalysts with the same 1,3-diether internal donor

Being the main responsible for the huge production of polyolefins, heterogeneous Ziegler-Natta catalysts are among the most important catalysts in the chemical industry and they have been optimized over the years since their discovery in 1953 crossing many different generations. Lastly, catalysts of the 5th generation are characterized by the introduction in the pre-catalyst of 1,3-diether compounds as internal electron donors, which are stable in the presence of AlR3 activators and do not require the further addition of external donors during the following steps of the catalytic process to control the activity and selectivity. In this work, we synthetized and systematically investigated by a multi-technique approach three Ziegler-Natta catalysts characterized by the same 1,3-diether donor, but differing in the synthesis route. We found that the synthetic route influences the MgCl2 particle size, as well as the properties of the Ti species. In particular, the reprecipitation method brings the smallest MgCl2 particles and the most positive Ti4+ sites in the pre-catalyst, but also the largest amount of accessible Ti3+ sites after TEAl activation. These structural and spectroscopic data correlate pretty well with the kinetic of gas-phase propylene polymerization in very mild conditions.

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.

Dual Photo‐ and Mechanochromisms of Graphitic Carbon Nitride/Polyvinyl Alcohol Film

AbstractAn adaptable stimuli responsive system is proposed based on defective graphitic carbon nitride (d‐GCN)/polyvinyl alcohol (PVA) composite attached to different substrates. Nitrogen vacancies, introduced during synthesis via potassium doping, act as internal electron donors to enhance the photoreduction of redox dyes for quick reversible photochromism. This system can be applied as visible light responsive rewritable paper that offers high resolution for printed text, rapid activation/recoloration, multicolor functionality, and high cyclability. The defects also inhibit the d‐GCN particle growth resulting in smaller particle sizes over bulk samples, which enable the formation of transparent mechanochromic films. By altering the PVA/d‐GCN ratio in the composites, two mechanical stimuli responses are introduced by taking advantage of wrinkle and crack formation on the film surface. With a low d‐GCN concentration, mechanical scratching of the film causes the formation of surface wrinkles that alter the film transparency without damaging the film, allowing for text to be written on the surface that can be erased by moisture. With a high d‐GCN concentration, cracks developed on the surface scatter light when stretched, enabling the development of a strain dependent smart window. Both these mechanochromisms can be combined with the photochromism to develop multifunctional smart materials with widespread application.

On-Demand Regulation of Photoreversible Color Switching for Rewritable Paper and Transient Information Encryption.

The achievement of photoreversible color switching systems (PCSS) has offered great opportunities for fundamental studies and practical applications. However, the development of PCSS that possessing highly reversible cyclability and on-demand regulation of recoloration process remains a grand challenge. Herein, we report a hydrazine-mediated self-doping strategy for the synthesis of alkaline Ti3+ self-doped TiO2-x nanoparticles, enabling the TiO2-x nanoparticles/methylene blue based PCSS with long photoreversible cyclability and rapid color switching rate. The Ti3+ species as internal sacrificial electron donors significantly improve the photoreductive activity of TiO2-x nanoparticles, which results in fast decoloration rate and long cycling number of the PCSS. Simultaneously, the alkaline property of TiO2-x nanoparticles enhances the oxidation kinetics of the PCSS to dramatically accelerate the recoloration rate. Moreover, the PCSS can be integrated elaborately with biodegradable agarose to form flexible color switching films, which exhibit long-waited on-demand regulation of recoloration rate in a wide range. By taking advantage of photoreversible color switching and time-resolved color changing process, we demonstrate their potential application in self-erasing rewritable paper and transient optical information encryption. This work represents a new strategy for the future development of PCSS and their advanced applications.

Synthesis of novel Ziegler Natta catalyst in the presence of internal promoter and electron donors for ethylene and ethylene/ 1-hexene polymerization

Synthesis of novel Ziegler Natta catalyst in the presence of internal promoter and electron donors for ethylene and ethylene/ 1-hexene polymerization

Inversion of the Photogalvanic Effect of Conductive Polymers by Porphyrin Dopants

Conductive polymers are widely used as active and auxiliary materials for organic photovoltaic cells due to their easily tunable properties, high electronic conductivity, and light absorption. Several conductive polymers show the cathodic photogalvanic effect in pristine state. Recently, photoelectrochemical oxygen reduction has been demonstrated for nickel complexes of Salen-type ligands. Herein, we report an unexpected inversion of the photogalvanic effect caused by doping of the NiSalen polymers with anionic porphyrins. The observed effect was studied by means of UV-Vis spectroscopy, cyclic voltammetry and chopped light chronoamperometry. While pristine NiSalens exhibit cathodic photopolarization, doping with porphyrins inverts the polarization. As a result, photoelectrochemical oxidation of the ascorbate proceeds smoothly on the NiSalen electrode doped with zinc porphyrins. The highest photocurrents were observed on NiSalen polymer with o-phenylene imine bridge, doped with anionic zinc porphyrin. Assuming this, porphyrin serves both as a catalytic center for the oxidation of ascorbate and an internal electron donor, facilitating the photoinduced charge transport and anodic depolarization.

Sustainable rosin acid ester as internal electron donors in Ziegler-Natta catalysts for synthesis of isotactic polypropylene with high melt flow rate

In this contribution, novel bio-derived rosin acid ester compounds have been developed and used as internal electron donors to prepare MgCl2 supported titanium catalysts for propylene polymerization. The results of the polymerization showed that tri-n-amyl maleate, triiso-amyl maleate and tri-n-heptyl maleate as internal electron donors in Ziegler-Natta catalysts all have high polymerization activity and stereoregularity. In particular, the Ziegler-Natta catalyst with tri-n-amyl maleate as the internal electron donor has the highest activity (up to 33.4 kgPP·gCat−1·h−1) for propylene polymerization and the isotacticity of polypropylene is as high as 96.8% determined by 13C NMR. Simultaneously, the obtained polypropylene with a relatively broad molecular weight distribution of 9.0 and melt flow rate of 160.3 g/10 min, which is beneficial to processing and has practical industrial application value when used as the basic material of melt blown cloth for medical mask.

Modification of the Acyl Chloride Quench-Labeling Method for Counting Active Sites in Catalytic Olefin Polymerization

The reliable and efficient counting of active sites in catalytic olefin polymerization has been realized by using acyl chloride as the quench-labeling agent. However, the molar ratio of acyl chloride to the alkylaluminum cocatalyst must be larger than 1 in order to completely depress side reactions between the quencher and Al-polymeryl that is formed via chain transfer reaction. In this work, a tetrahydrofuran/thiophene-2-carbonyl chloride (THF/TPCC) mixture was used as the quenching agent when counting the active sites of propylene polymerization catalyzed by MgCl2/Di/TiCl4 (Di = internal electron donor)-type Ziegler–Natta catalyst activated with triethylaluminum (TEA). When the THF/TEA molar ratio was 1 and the TPCC/TEA molar ratio was smaller than 1, the [S]/[Ti] ratio of the polymer quenched with the THF/TPCC mixture was the same as that quenched with only TPCC at TPCC/TEA > 1, indicating quench-labeling of all active sites bearing a propagation chain. The replacement of a part of the TPCC with THF did not influence the precision of active site counting by the acyl chloride quench-labeling method, but it effectively reduced the amount of acyl chloride. This modification to the acyl chloride quench-labeling method significantly reduced the amount of precious acyl chloride quencher and brought the benefit of simplifying polymer purification procedures after the quenching step.

Comparison of Mg-ethoxide based Ziegler Natta catalysts using different internal donors employed for ethylene polymerization

The effect of two types internal electron donors (IDs) on Mg-ethoxide based ZN catalysts employed for ethylene polymerization, was investigated using three similar catalysts with different IDs. P-cat (containing di isobutyl phthalate), S-cat (containing tetra ethoxy silane) at a constant molar ratio ID/Mg = 0.1, and N-cat (with no electron donor) were analyzed by FTIR, XRD, SEM, PSD, and BET. Some of available data of an Industrial catalyst (I-cat) were added to compare. FT-IR spectroscopy in transmission mode confirmed the presence of each electron donor in the catalyst. X-ray patterns of the catalysts showed that the disordered structure of δ-MgCl2 was formed in each catalyst and IDs in this manner do not influence the crystallinity of the support. This study showed that the use of IDs has a great influence on the resulting catalyst morphology (particle size and porosity) so that S-cat has the lower particle size and higher porosity but P-cat has the highest particle size and the lowest porosity. Ethylene polymerization was performed using catalysts under the same set of conditions (time, temperature, and Al/Ti) and in the presence of high pressure hydrogen. Then to better compare, an industrial catalyst (I-cat) was also used in this condition and the result were compared by the synthesized catalysts. The activity of catalysts with various kinds of IDs is in the following order: S-cat > N-cat > I-cat > P-cat. To better comparison, the kinetic polymerization rate of catalysts was fitted by a simple model and showed that the P-cat activated more slowly than others, I-cat has the fasten activation and deactivation rate, and S-cat has the highest propagation rate constant. IDs can change the active site behavior against hydrogen by affecting on the chain lengths measured by MFR value and molecular weight distribution. DSC analysis of the polymers showed the IDs can change the crystalline content of homo polyethylene. So that polymer obtained from P-cat and N-cat have more crystalline ( $$\approx$$ 80%) but polymer from S-cat has lower crystalline content ( $$\approx$$ 65%). Polymers with higher crystallinity also have lower molecular weight value. The polymer Bulk density as an important industrial parameter are presented for the catalysts.

Using ultrasonic treated sludge to accelerate pyridine and p-nitrophenol biodegradation

Aerobic biomass (acclimated activated sludge) was treated by ultrasound and used to accelerate biodegradations of pyridine and p-nitrophenol (PNP), which begin with mono-oxygenation reactions that need an internal electron donor. Ultrasound treatment disrupted the biomass and produced more soluble and (especially) colloidal organic material. Compared with untreated biomass, pyridine- and PNP-biodegradation rates increased when treated biomass provided electron donor. Pyridine- and PNP-biodegradation rates increased by 10% and 20%, respectively, over the control experiments when supernatants from treated biomass were added into the medium. For accelerating pyridine- and PNP removal rates, adding supernatants of treated biomass was equivalent to adding succinate of 0.35 mmol/L and 0.21 mmol/L, respectively. The rates were increased by 63% for both substrates when the entire treated biomass was added. Colloidal solids in the treated biomass contained most of biodegradable electron donor able to stimulate initial monooxygenations of pyridine and PNP. Adding treated biomass together with untreated biomass gave a synergistic impact on enhancing pyridine and PNP biodegradation, because the treated biomass supplied extra donor, while the untreated biomass maintained a high level of active biomass.

Direct Preparation of Transparent Isotactic Polypropylene with Supported Ziegler–Natta Catalysts Containing Novel Eco-friendly Internal Electron Donors

This study reported novel eco-friendly Ziegler-Natta catalysts containing bio-derived maleic rosinate tri-n-butyl and maleic rosinate tri-n-octyl as internal electron donors for propylene polymeriz...

Role of a Multidentate Carbonate Donor in MgCl2-Supported Ziegler–Natta Olefin Polymerization Catalysis: An Experimental and Computational Approach

A new multidentate carbonate (3,3,3′,3′-tetramethyl-2,2′,3,3′-tetrahydro-1,1′-spirobiindane-5,5′,6,6′-tetracarbonate) is studied as a potential internal electron donor for Ziegler–Natta (Z–N) catal...

Deactivation Effect Caused by Catalyst-Cocatalyst Pre-contact in Propylene Polymerization with MgCl2-supported Ziegler-Natta Catalyst

Propylene slurry polymerization with a MgCl2-supported Ziegler-Natta catalyst containing internal electron donor was conducted after different durations of pre-contact of the catalyst with triethylaluminum cocatalyst. The number of active centers ([C*]/[Ti]) was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and measuring sulfur content in the polymer. The pre-contact treatment caused selective deactivation of a part of active centers with low stereoselectivity and much lower activity in the initial stage of polymerization as compared with the polymerization run without the pre-contact stage. The active center concentration and polymerization activity decreased with prolonging of the pre-contact stage. The proportion of stereoselective active centers was increased by prolonging the pre-contact stage, so the isotacticity of produced polypropylene was enhanced. Release of active centers through catalyst particle fragmentation was significantly retarded, and the polymerization rate curve changed from decay type to induction type by the precontact treatment. In the induction period both non-stereoselective and stereoselective active centers were released and activated, resulting in gradual reduction of the polymer’s isotacticity in the first 5–10 min of polymerization. Selective deactivation of non-stereoselective active centers also took place in propylene polymerization using the catalyst without pre-contacting with the cocatalyst. In this case, the polymerization rate decayed with time after a short induction period of 2–5 min. Over reduction of the active center precursors with low stereoselectivity by triethylaluminum was considered as the reason for their deactivation during the pre-contact or the polymerization processes.