Evolutionary Catalyst Screening: Iridium‐Catalyzed Imine Hydrogenation

A high throughput catalyst screening is presented employing an evolutionary approach. The method comprises the optimization of initial leads by subjecting the catalysts to iterative rounds of optimization, including structural elaboration of the ligands by creating new focused libraries. Highly modular supramolecular ligands, robotized synthesis combined by high throughput experimentation creates a platform for fast catalyst development. An illustrative example for the asymmetric hydrogenation of cyclic 2,3,3‐trimethyl‐3H‐indole using iridium catalysts is presented. The kinetic investigation of the best catalyst yields an unusual second order in iridium, first order in hydrogen and zeroth order in substrate. Under optimized reaction conditions a TOF of 100 mol mol⁻¹ h⁻¹ with 96% ee could be obtained with the best catalyst. A full catalyst screening and kinetic study was conducted within a three‐week time‐frame.     

Carrageenan: A Food‐Grade and Biocompatible Support for Immobilisation Techniques

Immobilisation of both enzymes and whole‐cell systems is of major importance in the improvement of the stability, activity and reusability of these biocatalysts. This review describes the use of the naturally occurring polysaccharide carrageenan as a support for the immobilisation of biocatalysts. Carrageenan is a food‐grade and biocompatible support material extracted from red seaweeds. Before focusing on the use of carrageenan as an immobilisation support, an overview is given of the present uses of biocatalysts in industrial processes. The basic concepts of enzyme and whole‐cell immobilisation are discussed, as well as the background of carrageenan as a biopolymer. Several examples of enzymes and whole‐cell systems immobilised in carrageenan are discussed. A list of the most relevant patents in this field is presented as well as a list of enzymes and cell systems immobilised in carrageenan as described in the literature.     

Fully Automated Reactor System for Continuous Characterization of (Bio)catalysts

The existing screening and characterization systems for biocatalysts operate in batch mode, which could make catalyst selection and process development inaccurate when continuous operation mode is required in industry. A significant improvement of an innovative screening system based on miniaturized multiple membrane reactors formerly presented by the author is outlined, which enables continuous feeding of substrates and continuous removal of products. Although the presented screening system was originally designed for homogeneous enzymatic reactions, it can be used without further modifications for continuous catalysis with polymer‐bound chemical catalysts or for quasi‐homogeneous systems like reverse micelles.     

Influence of supported vanadium catalyst on ethylene polymerization reactions

BACKGROUND: In the research area of homogeneous Ziegler–Natta olefin polymerization, classic vanadium catalyst systems have shown a number of favourable performances. These catalysts are useful for (i) the preparation of high molecular weight polymers with narrow molecular weight distributions, (ii) the preparation of ethylene/R‐olefin copolymers with high R‐olefin incorporation and (iii) the preparation of syndiotactic polypropylenes. In view of the above merits of vanadium‐based catalysts for polymerization reactions, the development of well‐defined single‐site vanadium catalysts for polymerization reactions is presently an extremely important industrial goal. The main aim of this work was the synthesis and characterization of a heterogeneous low‐coordinate non‐metallocene (phenyl)imido vanadium catalyst, V(NAr)Cl₃, and its utility for ethylene polymerization. RESULTS: Imido vanadium complex V(NAr)Cl₃ was synthesized and immobilized onto a series of inorganic supports: SiO₂, methylaluminoxane (MAO)‐modified SiO₂ (4.5 and 23 wt% Al/SiO₂), SiO₂? Al₂O₃, MgCl₂, MCM‐41 and MgO. Metal contents on the supported catalysts determined by X‐ray fluorescence spectroscopy remained between 0.050 and 0.100 mmol V g^?1 support. Thermal stability of the catalysts was determined by differential scanning calorimetry (DSC). Characterization of polyethylene was done by gel permeation chromatography and DSC. All catalyst systems were found to be active in ethylene polymerization in the presence of MAO or triisobutylaluminium/MAO mixture (Al/V = 1000). Catalyst activity was found to depend on the support nature, being between 7.5 and 80.0 kg PE (mol V)^?1 h^?1. Finally, all catalyst systems were found to be reusable for up to three cycles. CONCLUSION: Best results were observed in the case of silica as support. Acid or basic supports afforded less active systems. In situ immobilization led to higher catalyst activity. The resulting polyethylenes in all experiments had ultrahigh molecular weight. Finally, this work explains the synthesis and characterization of reusable supported novel vanadium catalysts, which are useful in the synthesis of very high molecular weight ethylene polymers. Copyright © 2007 Society of Chemical Industry     

Zinc(II)‐triflate as catalyst precursor for ring‐closing depolymerization of end‐of‐life polytetrahydrofuran to produce tetrahydrofuran

The recycling of polymers continues to be an important subject for a greener and sustainable society. Especially, the deconstruction of end‐of‐life polymers to monomers creates a feedstock for new high‐quality polymeric materials and contributes to conserve resources and allow an efficient waste‐managing system. In this study, zinc(II)‐triflate as catalyst precursor has been examined in detail In the ring‐closing depolymerization of end‐of‐life polytetrahydrofuran (PolyTHF) to generate tetrahydrofuran (THF). Noteworthy, the produced THF can be a suitable starting material for new polymeric materials. With the cheap and abundant Zn(OTf)₂ (1.0 mol %) as precatalyst excellent yields (up to 95%) were feasible for the depolymerization of PolyTHF at 180°C within 30 min. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39791.     

Further studies on styrene/styrene derivative copolymerizations using combined diphenylzinc‐additive initiator systems

A combination of diphenylzinc, a metallocene and methylaluminoxane (Ph₂Zn‐metallocene‐MAO) is a suitable initiator system for the polymerization of styrene and for its copolymerization with para‐alkyl substituted styrenes. This paper reports new experimental results which reinforce our previous findings indicating that polymerization processes are initiated by monomer coordination to active species resulting from these particular combined systems. Polymerization propagates by a cationic pathway. Further to our previous observation that the I+ inductive effect of para‐substituents in styrene improves conversion to polymer, we now find that methyl substitution on the vinyl double bond of styrene, in spite of the I+ inductive effect and as a result of increased steric hindrance, makes the polymerization process difficult. On the other hand, the replacement of titanocenes by zirconocenes or hafnocenes generates Ph₂Zn‐metallocene‐MAO initiator systems which are also able to induce homo‐ and copolymerization, but with lower yields and producing practically amorphous polymers. The efficiency of our Ph₂Zn‐metallocene‐MAO initiator systems follows the order titanocene > zirconocene > hafnocene, at least for the studied metallocenes. Copyright © 2004 Society of Chemical Industry     

Immobilization of catalase on a novel polymer support,crosslinked polystyrene ethylene glycol acrylate resin: Role of the macromolecular matrix on enzyme activity

Crosslinked polystyrene ethylene glycol acrylate resin (CLPSER) was developed for the immobilization of the enzyme catalase by the introduction of a crosslinker, O,O′‐bis(2‐acrylamidopropyl) poly(ethylene glycol)₁₉₀₀, to styrene. The crosslinker was prepared by the treatment of acryloyl chloride with O,O′‐bis(2‐aminopropyl) poly(ethylene glycol)₁₉₀₀ in the presence of diisopropylethylamine. The resin was characterized with IR and ¹³C‐NMR spectroscopy. The catalytic activity of the catalase‐immobilized system of CLPSER was compared with divinylbenzene‐crosslinked polystyrene, ethylene glycol dimethacrylate crosslinked polystyrene, and 1,4‐butanediol dimethacrylate crosslinked polystyrene systems. Crosslink levels of 2, 8, and 20 mol % were evaluated. Among these crosslinked systems, the 2 mol % system was found to be most suitable to support catalytic activity. When a long flexible hydrophilic poly(ethylene glycol) crosslink, introduced between the polystyrene (PS) backbone and functional groups was used for immobilization, the extent of coupling and enzyme activity increased. Depending on the nature of the support, the catalytic activity of the system varied. The hydrophilic CLPSER support was most efficient for immobilization compared to the other PS‐based supports. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 8–19, 2005     

Novel catalysts based on titanium dioxide/silicon dioxide for poly(ethylene terephthalate)

A series of titanium dioxide/silicon dioxide based poly(ethylene terephthalate) (PET) polycondensation catalysts were synthesized with different Si/Ti molar ratios and various amounts of polyvinylpyrrolidone (PVP). The composition, structure, and catalytic activities of the catalysts and the properties of the PET samples catalyzed by these catalysts were characterized with thermogravimetric analysis, electron probe microanalysis, X‐ray diffraction, X‐ray photoelectron spectroscopy, and so forth. The results indicated that the Si/Ti molar ratios of the catalysts could be well controlled by the synthesis processes used in this study, whereas the content of PVP was influenced by the amount of titanium dioxide. The activities of the catalysts greatly depended on the Si/Ti molar ratios and coordinative effects between titanium and PVP. Some of the catalysts possessed ultrahigh activities, and the corresponding PET material had excellent properties.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Laboratory‐Scale Method for Estimating Explosive Performance from Laser‐Induced Shock Waves

A new laboratory‐scale method for predicting explosive performance (e.g., detonation velocity and pressure) based on milligram quantities of material is demonstrated. This technique is based on schlieren imaging of the shock wave generated in air by the formation of a laser‐induced plasma on the surface of an energetic material residue. The shock wave from each laser ablation event is tracked for more than 100 μs using a high‐speed camera. A suite of conventional energetic materials including DNAN, TNT, HNS, TATB, NTO, PETN, RDX, HMX, and CL‐20 was used to develop calibration curves relating the characteristic shock velocity for each energetic material to several detonation parameters. A strong linear correlation between the laser‐induced shock velocity and the measured performance from full‐scale detonation testing has been observed. The Laser‐induced Air Shock from Energetic Materials (LASEM) method was validated using nitrocellulose, FOX‐7, nano‐RDX, three military formulations, and three novel high‐nitrogen explosives currently under development. This method is a potential screening tool for the development of new energetic materials and formulations prior to larger‐scale detonative testing. The main advantages are the small quantity of material required (a few milligrams or less per laser shot), the ease with which hundreds of measurements per day can be obtained, and the ability to estimate explosive performance without detonating the material (reducing cost and safety requirements).     

Heterogeneous catalytic synthesis of poly(butylene succinate) by attapulgite‐supported Sn catalyst

An attapulgite‐supported Sn catalyst (Sn‐palgorskite) was successfully prepared by ion‐exchange co‐impregnation method. The catalytic effect of Sn‐attapulgite on the melt polycondensation reaction of poly(butylene succinate) (PBS) was examined by comparing with that of anhydrous SnCl₂ and a blank experiment. The structures and properties of the PBS products synthesized with the three catalytic systems were characterized by means of Fourier transform‐infrared spectra (FT‐IR), viscosity measurements, wide angle X‐ray diffraction (WARD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Meanwhile, the acidolysis degradation behaviors of the PBS samples were also studied. It was found that the intrinsic viscosities and the number‐average molecular weights of the PBS were remarkably increased under the catalysis of Sn‐attapulgite, further leading to an increase in the decomposition temperature, the crystallization temperature, and the viscous flow activation energy, while a decrease in the melting temperature, the relative degree of crystallinity, and the rate of degradation. Additionally, no significant differences were observed in the crystal structures of all the samples, regardless of the reaction system with or without catalyst. The experiment results confirmed that Sn‐attapulgite was an effective heterogeneous catalyst for the synthesis of PBS, and the recycled Sn‐attapulgite still exhibited higher activity than anhydrous SnCl₂ under identical reaction conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41729.     

Phenolic‐epoxy matrix curable by click chemistry—synthesis,curing, and syntactic foam composite properties

Alkyne functional phenolic resin was cured by azide functional epoxy resins making use of alkyne‐azide click reaction. For this, propargylated novolac (PN) was reacted with bisphenol A bisazide (BABA) and azido hydroxy propyloxy novolac (AHPN) leading to triazole‐linked phenolic‐epoxy networks. The click cure reaction was initiated at 40–65°C in presence of Cu₂I₂. Glass transition temperature (Tg) of the cured networks varied from 70°C to 75°C in the case of BABA‐PN and 75°C to 80°C in the case of AHPN‐PN. DSC and rheological studies revealed a single stage curing pattern for both the systems. The cured BABA‐PN and AHPN‐PN blends showed mass loss above 300°C because of decomposition of the triazole rings and the novolac backbone. Silica fiber‐reinforced syntactic foam composites derived from these resins possessed comparable mechanical properties and superior impact resistance vis‐a‐vis their phenolic resin analogues. The mechanical properties could be tuned by regulating the reactant stoichiometry. These low temperature addition curable resins are suited for light weight polymer composite for related applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41254.     

Microstructure of isotactic polypropylene obtained using Ziegler–Natta catalyst at high polymerization temperature

The microstructure of the isotactic polypropylene obtained with various MgCl₂‐supported catalyst systems at high polymerization temperature of 70–100°C is investigated by discussing the intrinsic relation between the different types of active centers and the polymerization temperatures via gel permeation chromatography, temperature rising elution fractionation, and ¹³C NMR. For the MgCl₂/TiCl₄/di‐n‐butyl phathalate‐AlEt₃/external donor and MgCl₂/TiCl₄/2,2‐diisobutyl‐1,3‐dimethoxypropane‐AlEt₃ catalyst systems, the differences in the isotactic productivity of polymers obtained at different polymerization temperatures mainly result from the variation of both the activity of the different isospecific active centers and the stability constants of the complex of catalyst/donor. The reaction rate of high isotactic active centers reaches maximum at 85–90°C, and this effect contributes to both the highest isotacticity and the narrowest molecular weight distribution. For the MgCl₂/TiCl₄/phthalate ester‐AlEt₃ catalyst system, the isotacticity of polypropylene remains approximately constant in the temperature range of experiments, which could be ascribed to elution of phthalate ester after the activation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42487.     

Isobutylaluminum aryloxides as metallocene activators in Homo‐ and copolymerization of olefins

The article describes that sterically hindered isobutylaluminum aryloxides with bulky ^tBu substituents at 2,6‐ positions of aryl fragment, i.e. (2,6‐di‐^tBu,4‐R‐C₆H₂O)AlⁱBu₂ (R = H ( 1‐DTBP ), Me ( 1‐BHT ), ^tBu ( 1‐TTBP )) and (2,6‐di‐^tBu,4‐R‐C₆H₂O)₂AlⁱBu (R=H( 2‐DTBP ), Me( 2‐BHT )) can serve as cocatalysts for metallocene complexes. Isobutylaluminum aryloxides have been applied for activation of rac‐Et(2‐MeInd)₂ZrMe₂ in homopolymerization of ethylene, propylene, copolymerization of ethylene and propylene, and terpolymerization of ethylene, propylene, and 5‐ethylidene‐2‐norbornene at Al/Zr = 300 mol/mol. The type of R substituent at 4‐position has a significant effect on catalyst activity. The catalytic system with 1‐TTBP showed the highest activity in all homo‐ and copolymerization processes. Diisobutylaluminum aryloxides provide much higher activity to the systems in all polymerization processes and stronger ability for propylene incorporation in copolymer than diaryloxides. The activities of the systems with isobutylaluminum aryloxides are similar or exceed that of the system with MAO as activator as have shown for propylene polymerization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43276.     

An Innovative Technique for Rapid Screening of Cigarette Filter Adsorbents

Cigarette smoke is an aerosol containing a large number of chemicals, including toxicants. In recent years, a number of cigarette filter additives have been evaluated for their toxicant filtration properties. Screening is a useful tool to accelerate the testing and development of new filter additives and filtration mechanisms. The evaluation of a filter material screening technique based on the so‐called InfraSORP technology is described. By comparing InfraSORP measurements with reference cigarette smoke experiments of potential cigarette filter materials like activated carbons and ion‐exchange resin, an excellent correlation is demonstrated. This technique allows for a rapid screening of potential filter materials prior to testing any final candidates in cigarettes.     

Polymer precursor to diamondlike carbon prepared by the polymerization of α,α,α‐trichlorotoluene and acetonitrile

A novel liquid/solid two‐phase reaction of α,α,α‐trichlorotoluene (PhCCl₃) and acetonitrile (AN) has been discovered that produces a carbon‐based polymer with diamondlike structure at the atomic level. The solid phase is potassium hydroxide particles, and the liquid phase is a tetrahydrofuran solution of PhCCl₃ and AN containing a certain amount of tetrabutylammonium bromide as a phase‐transfer catalyst. The structure of the carbon‐based polymer has been characterized by elemental analysis, Fourier transform infrared spectroscopy, and ¹H‐ and ¹³C‐NMR spectroscopy. The pyrolysis of the carbon‐based polymer at 800°C under a nitrogen atmosphere leads to the formation of a diamondlike carbonaceous material according to the results of X‐ray photoelectron spectroscopy and Raman spectroscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 16–23, 2003     

Selection of Biphasic Liquid Systems in Liquid‐Liquid Chromatography Using Predictive Thermodynamic Models

The possibility of using thermodynamic models for screening biphasic liquid systems, including systems for which liquid‐liquid equilibrium data are not available, is demonstrated. The liquid‐liquid equilibrium in different biphasic systems and the partition coefficients of solutes in these systems are predicted with UNIFAC and COSMO‐RS. The predictions are based only on the molecular structure of the solutes and solvents. The advantages and limitations of the two models are explored using fourteen solutes and five biphasic solvent systems. The overall results show that the theoretically selected systems closely match the systems chosen by experimental screening. The experimental work needed for selecting a suitable biphasic system for a given separation problem can be drastically reduced with the help of predictive thermodynamic models.     

High-throughput preparation and screening of rhenium oxide-alumina catalysts in olefin metathesis

High-throughput (HT) experimentation in heterogeneous catalysis exemplifies a multidisciplinary approach to address in an efficient manner different aspects of catalyst development – from synthesis to testing and characterization. The present work reports on preparation systems for rapid parallel synthesis of well defined heterogeneous catalysts and catalyst screening in olefin metathesis. Metathesis of ethene and but-2-ene to propene was chosen as a test reaction. The influences of various parameters such as rhenium oxide loading, catalyst calcination conditions, catalyst pre-treatment, as well as the reaction temperature and contact time on the catalytic performance are discussed. Sample characterization by UV–vis and FT-IR gave an evidence for the formation of active surface perrhenate species, very sensitive to humidity and pre-treatment conditions applied.     

Describing and quantifying the chemical composition distribution in unimodal and multimodal ZN‐polyethylene using CRYSTAF

A new approach in describing and quantifying the chemical composition distribution (CCD) in Ziegler–Natta‐polyethylene copolymers was developed by using crystallization analysis fractionation (Crystaf). Copolymers of ethylene and α‐olefins (1‐butene and 1‐hexene) polymerized with different ZN catalyst systems were analyzed. Distinct differences in the CCD between the different polymer types (catalyst‐cocatalyst system and comonomer type) were observed and could be quantified. Same approach was applied to 2‐dimensional fractionation technique, cross fractionation chromatography, to describe and quantify the CCD of multimodal polyethylene copolymers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43089.     

Homopolymerization of n‐butyl methacrylate using bis(salicylaldiminate)copper(II)/ methylaluminoxane catalysts

Polymerization catalysts based on copper precursors appear particularly interesting due to the low metal cost, limited toxicity and modest sensitivity to deactivation by polar species. To date, α‐olefin and polar monomer coordination polymerization catalysed using copper catalysts has been scarcely investigated, and a good part of the literature is represented by patents. Here this research has been expanded to the study of the performances of bis(salicylaldiminate)copper(II)/methylaluminoxane (MAO) catalysts in the polymerization of n‐butyl methacrylate. The study of the catalytic activity of bis(salicylaldiminate)copper(II)/MAO systems in n‐butyl methacrylate polymerization was focused on the relationship between the catalytic behaviour and the main reaction conditions and ligand structures. The electronic and steric characteristics of the chelate ligands play an important role in the catalytic performances. The presence of electron‐withdrawing nitro groups on the chelate ligands increased the catalytic activity which reached 36 kg_polymer mol^?1 h^?1, the highest value up to now reported for copper systems in methacrylic or acrylic monomer polymerization. These performances were ascribed to copper catalysts activated by MAO: without copper precursor, working in the presence of MAO and free salicylaldimine ligand, complete inactivity was ascertained. Copyright © 2010 Society of Chemical Industry     

Cationic polymerization of 1,3‐pentadiene coinitiated by zinc halides

Technology of industrial production of liquid rubber under trademark “SKOP” is based on the cationic polymerization of 1,3‐penadiene (piperylene) in the presence of TiCl₄ or AlCl₃‐based catalytic systems. The disadvantage of these catalytic systems is the high probability of formation of branched and insoluble fractions due to the chain transfer to polymer. This deteriorates the useful qualities of SKOP. Here we propose the new initiating systems for the cationic polymerization of 1,3‐pentadiene based on the homogeneous (dissolved in a minimal amount of diethyl ether) zinc halides (ZnCl₂ and ZnBr₂) as coinitiators and hydrochloric acid, tert‐butyl chloride or trichloroacetic acid as initiators. These initiating systems allow to synthesize fully soluble low molecular weight (M_n = 1000–3000 g mol^?1) poly(1,3‐pentadiene)s with relatively narrow molecular weight distribution (M_w/M_n < 2.0), which do not contain any high molecular weight and insoluble fractions in the whole range of monomer conversion. The polymers synthesized in the presence of zinc halides possess the same microstructure that those prepared with TiCl₄ as coinitiator. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013