Search Results (222)

This study examines the influence of the chemical nature and molecular structure of external electron-donor compounds on the slurry synthesis of isotactic polypropylene in a hydrocarbon diluent using a titanium–magnesium Ziegler–Natta catalyst. Propylene polymerization was carried out at constant temperature, pressure, hydrogen concentration, and fixed molar ratios of the catalyst system components. Alkoxysilanes with different structures were used as external donors: dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane, diisobutyldimethoxysilane, and diethylaminotriethoxysilane; di-n-butyl phthalate was used as a reference compound. It was shown that external donors decrease catalytic activity relative to the donor-free system but increase stereospecificity, as indicated by a lower xylene-soluble fraction and a higher isotactic index of polypropylene. Dicyclopentyldimethoxysilane demonstrated the strongest stereoregulating effect, providing the lowest content of xylene-soluble polymer. The donor structure significantly affected the molecular weight, rheological, and thermal characteristics of polypropylene, including melt flow rate, viscosity-average molecular weight, melting temperature, melting enthalpy, and crystallinity. Comparison with literature data for catalyst systems differing in internal and external donors, as well as in synthesis conditions, showed that catalyst activity and the stereospecificity of the catalyst system may be determined not only by process parameters but also by the electron-donor environment of the active sites. The results support established concepts of external-donor action in Ziegler–Natta catalysis and provide a comparative assessment of alkoxysilane donors and di-n-butyl phthalate under slurry polymerization conditions. Full article

Recent advancements in heterogeneous catalysis have increased the interest in the synthesis of metal-free polymer-based catalysts. This work presents a novel approach for the solvent- and additive-free synthesis of a nitrogen-rich catalyst. Our unique procedure yields a non-porous organic polymer (NPOP) with a wide range of functional groups on the surface, attributed to the incomplete polymerization inherent to our solvent-free method. Detailed analysis revealed significant differences between NPOP and its Covalent Organic Framework counterpart. Remarkably, the absence of a high surface area did not hinder the efficiency of NPOP as a catalyst for the CO₂ cycloaddition. The performance of NPOP exceeded that of its COF counterpart, with a conversion rate of 99% for NPOP and 35% for the COF. An observation attributed to the abundance of nitrogen functional groups on the surface of NPOP. A combination of characterizations and density functional theory (DFT) calculations was employed to thoroughly understand the working mechanism of NPOP. The imines and secondary amines on the surface function as the active sites for the ring-opening of epichlorohydrin. This study supports existing theories that N atoms can serve as nucleophiles by donating their free electron pairs. Furthermore, the distinctive synthesis procedure reported here can serve as inspiration for further design of polymer-based catalysts. Full article

Magnesium oxide (MgO) nanoparticles, recognized for their versatile applications from catalysis to biomedicine, require synthesis methods that offer precise control over their properties while ensuring safety and scalability. This study explores a safer, industrially viable adaptation of the polyacrylamide gel synthesis route by utilizing magnesium sulfate (MgSO₄) instead of conventional nitrates to mitigate explosion risks during calcination. A systematic study was conducted to evaluate the influence of key synthesis parameters, such as crosslinker ratio, initiator concentration, precursor loading, calcination conditions (including temperature, time, and heating rate), pH, and the use of chelating agents (EDTA and citric acid), on the purity, morphology, size distribution, and colloidal stability of the synthesized MgO nanoparticles. Characterization via X-ray spectroscopy XRF and XRD, acoustic spectroscopy, nitrogen physisorption (BET), electronic microscopy SEM and TEM and dispersion stability analysis revealed that polymeric cell volume (controlled by crosslinker and initiator) significantly influences size distribution, while chelating agents in alkaline environments drastically reduce particle size to ~20 nm and alter morphology to platelets (EDTA) or polygonal shapes (citric acid). Crucially, a low heating rate (2.5 °C/min) was found to yield smaller particles (~30 nm) and higher purity. This work provides a comprehensive blueprint for the tailored, safe, and scalable synthesis of MgO nanoparticles with targeted properties for specific technological applications. Full article

Poly(trimethylene ether) glycol (PO3G), a bio-based polyether polyol with excellent flexibility and superior hydrolytic stability, has emerged as a critical raw material for the preparation of high-performance polymer materials. This work optimized the sulfuric acid-catalyzed polymerization process and assessed the feasibility of using p-toluenesulfonic acid (PTSA) as an alternative catalyst. A parametric study was conducted to establish a reliable operating window for the sulfuric acid system. DFT calculations demonstrated that the driving force for chain growth decreases with increasing chain length, that recombination between chains of significantly different lengths is more favorable than between chains of equal length, and that the formation of disulfate esters is thermodynamically more favorable. Although PTSA required a higher catalyst loading, the resulting polymer had a markedly lower yellowness index. Prolonged reaction times lead to a molecular weight plateau, especially at high PTSA concentrations, while the yellowness index continues to increase after reaching the plateau. ¹H NMR analysis indicated the formation of benzenesulfonate monoester intermediates during PTSA catalysis, suggesting a potentially milder pathway and possibly fewer side reactions compared to the sulfuric acid system. This paper provides theoretical and experimental foundations for the green, efficient synthesis of PO3G and the catalyst optimization for analogous bio-based polyether polyols. Full article

This review summarizes recent applications of nuclear magnetic resonance (NMR) in olefin polymerization catalysis. Due to its capability for quantitative characterization of molecular structures and in situ study, NMR is employed to study the structure of catalysts, and to trace catalyst/cocatalyst interactions, the evolution of active species, monomer insertion, and chain-end formation. This review emphasizes the activation mechanisms of molecular catalysts, ion-pair structures, and the measurement of kinetics. It also discusses the potential applications of in situ multinuclear NMR and isotope labeling technologies in olefin polymerization catalysis studies. Full article

The incorporation of polar functional groups into polyethylene (PE) chains at controlled concentrations enables tailored multi-functionality, manifesting as printability enhancement, improved dyeability, and enhanced blending compatibility with diverse polymeric materials. The most effective way to incorporate polar monomers into the PE macromolecules is the transition metal-mediated coordination–insertion copolymerization of ethylene with polar monomers. However, the Lewis basic heteroatoms (N, O, S, P, etc.) in polar monomers are prone to strongly coordinate to the catalytic center, resulting in irreversible catalyst deactivation. Owing to the nature of tolerance to Lewis basic functionalities, rationally designed Pd and Ni complexes have proven to catalyze direct coordination polymerization of ethylene with polar monomers, which opened a practical way to prepare functionalized polyethylenes (F-PEs). In this context, we summarize the recent advances of the Pd and Ni complexes catalyzed copolymerization of ethylene with various polar monomers, especially focused on those commercial polar monomer feedstocks. In addition, the effects of metal, ligand structural modification, and additives regulation on the catalytic performances were analyzed in detail. Some key ideas on the salient aspects of the catalyst are presented, and the challenges and prospects of Pd and Ni catalysts in the polar monomer copolymerization problems are also discussed. Full article

X-ray crystallography is still the most widely used and versatile method for structural studies of biological macromolecules. This study concerns the application of nanogels to facilitate protein crystallization, a prerequisite for X-ray crystallography. Nanogels (NGs) are nano-sized, highly crosslinked polymeric particles that have been extensively studied for chemical catalysis and drug delivery but not for protein crystal nucleation. The efficacy of six types of nanogels (three N-isopropylacrylamide-based and three acrylamide-based) was tested, with promising results. They were subsequently functionalised with active hydroxyl groups for further testing. Both functionalised and non-functionalised nanogels were tested on model (trypsin, thaumatin, proteinase K, ferritin and catalase) and target proteins (glulisine, α-crustacyanin and acriflavine resistance protein subunit AcrB) using both manual and automated techniques. All nanogels were found to be effective in promoting protein crystallization in both screening and optimization trials, giving crystal ‘hits’ that would have otherwise been missed. Overall, the functionalised nanogels were more effective. Nanogel effects are proposed to be due to a combination of surface porosity and surface chemistry. Full article

Anilido-oxazoline iron(II) chloride complexes were synthesized and evaluated for their catalytic performance in the ring-opening polymerization (ROP) of cyclic esters. Complexes 1–5 were obtained via transmetalation of FeCl₂(THF)_1.5 and pyridine derivatives with in situ generated anilido-oxazoline lithium. They exhibited excellent controllability and high initiating efficiency in the ROP of ε-caprolactone (CL). In the presence of benzyl alcohol as the initiator, these iron complexes efficiently catalyzed the ROP of CL, reaching a TOF of 3.2 × 10³ h⁻¹. High molecular weight polycaprolactone was obtained with a number-average molecular weight of 161.38 kg/mol. The chain initiation and propagation processes were investigated using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and kinetic analyses. Kinetic studies confirmed a pseudo-first-order dependence of the polymerization rate on catalyst concentration. Furthermore, the iron(II) complexes were also found to be efficient catalysts for the ROP of δ-valerolactone. Full article

This review presents the covalent chemistry of carbon from the point of the spin-radical concept of electron interaction in the framework of the unrestricted molecular orbitals (UHF MO) theory. Using the language of valence bond trimodality, the regions of classical spinless spin-symmetric covalence and its spin-dependent asymmetric counterpart are defined. Carbon is the only element exhibiting spin covalent chemistry. Classical covalent chemistry of carbon of molecular substances whose valence bond structure includes segregate or chained single sp³$C-C$ bonds meet its spin counterpart only at these bonds breaking. Substances with double sp²$C=C$ and triple sp¹$C\equiv C$ bonds are the subject of spin covalent chemistry of carbon. The mathematical apparatus of the UHF MO allows forming algorithms controlling the chemical modification of carbon substances, polymerization processes, and catalysis involving them, making it possible to supplement the empirical spin covalent chemistry of carbon with its virtual analog. Full article

This study reports the synthesis and catalytic evaluation of a series of imidazolium-based polymeric ionic liquids (PILs) for the cycloaddition of CO₂ to epichlorohydrin (ECH). The synthesized catalysts include homopolymers, poly(3-hydroxyethyl-1-vinylimidazole chloride) (p[HVIm][Cl]) and poly(3-carboxymethyl-1-vinylimidazole chloride) (p[CMVIm][Cl]), and their block copolymers with polystyrene, synthesized for the first time, pS-b-p[HVIm][Cl] and pS-b-p[CMVIm][Cl]. Structural characterization by NMR, IR spectroscopy, and gel permeation chromatography confirmed the successful synthesis. The block copolymers exhibited a low polydispersity index (PDI 1.1–1.2), which is indicative of homogeneous chain lengths and the propensity to form ordered nanostructures, whereas the homopolymers showed higher PDI (2.4–2.9). Catalytic testing at 90 °C and 1 MPa CO₂ for 4 h revealed a clear activity trend: p[CMVIm][Cl] < p[HVIm][Cl] < pS-b-p[CMVIm][Cl] < pS-b-p[HVIm][Cl], with conversions exceeding 75% for all catalysts and a maximum of 82.69% for pS-b-p[HVIm][Cl]. These results demonstrate that the catalytic performance of PILs is governed by a synergistic interplay between the local chemical functionality of the ionic moiety and the overall polymer architecture. Based on these results, the synthesized polymeric ionic liquids, particularly pS-b-p[HVIm][Cl], demonstrate strong potential for creating multifunctional materials. Their ability to self-assemble into ordered nanostructures with distinct hydrophobic and hydrophilic domains provides a foundational architecture for combined gas separation and catalysis. The observed “micellar catalytic effect”, which enhances local reagent concentration near active sites, could be leveraged in a membrane reactor to simultaneously capture and convert CO₂ directly within the membrane. This integrated “separation–reaction” approach represents a promising strategy for advancing circular carbon economy technologies. Full article

Molecularly imprinted polymers (MIPs) are synthetic materials with highly selective recognition properties and are widely studied for applications in separation, sensing, catalysis, and biomedical analysis. However, conventional MIP synthesis often relies on toxic solvents and reagents, causing environmental and sustainability concerns. This review critically examines recent advances in the green synthesis of MIPs, focusing on strategies aligned with green chemistry principles. Emphasis is placed on the use of environmentally less toxic solvents, as well as bio-based and less hazardous functional monomers and crosslinkers. Emerging polymerization techniques, such as microwave-assisted, photochemical, and solvent-free approaches, are also discussed. The impact of green synthetic routes on the structural, physicochemical, and recognition properties of MIPs is analyzed, highlighting both benefits and current limitations. Finally, key challenges and future perspectives for the development of sustainable MIPs are outlined. Full article

Triacetin (TA) is a solvent commonly used in pharmaceutical and food applications, and as a plasticizer in bioplastics such as poly(lactic acid) (PLA) and cellulose acetate (CA). L-lactide is the monomer used in the ring-opening polymerization of PLA. The structure of TA emulsions stabilized by a cellulose hydrogel (CH) was imaged in this study. The emulsions were prepared by mechanical homogenization or a two-step process with subsequent high-pressure homogenization (HPH). The two-step process yielded smaller TA droplets and a more homogeneous CH dispersion. The images demonstrate that emulsion stabilization is due to CH particles adsorbed at the TA–water interface. The ester hydrolysis of TA and a lactide/TA solution by two industrially important lipases, from Candida rugosa (CRL) and Burkholderia cepacia (BCL), was investigated, assessing the effect of CH as an emulsion stabilizer. Mechanically homogenized TA emulsions were effectively hydrolyzed. Lactide was found to inhibit the enzymatic hydrolysis of TA. This inhibition was mitigated by CH for CRL-catalyzed hydrolysis but not for BCL catalysis. These results indicate a synergistic effect of CH stabilization on the interfacial activation of CRL. Thise effect may also be relevant for the biodegradation of bio-derived plastics and their fibrous cellulose composites. Full article

The aza-Michael reaction is a fundamental transformation for carbon–nitrogen bond formation, providing efficient access to β-amino carbonyl compounds, nitriles, and related nitrogen-containing building blocks of broad importance in medicinal chemistry and organic synthesis. Over the past two decades, ionic liquids (ILs) have attracted considerable attention as alternative reaction media, promoters, and catalysts for aza-Michael reactions, owing to their distinctive physicochemical properties and tunable structures. This review presents a comprehensive and critical overview of ionic-liquid-mediated aza-Michael reactions, emphasizing the evolution of IL design from early imidazolium-based systems to modern task-specific, supported, and bio-derived ionic liquids. Conventional room-temperature ionic liquids are discussed as non-innocent solvents capable of stabilizing charged intermediates and enhancing electrophilicity, thereby enabling catalyst-free or metal-assisted aza-Michael additions. Subsequent sections focus on task-specific ionic liquids incorporating Brønsted acidic, basic, hydrogen-bond-donating, or bifunctional motifs, highlighting how rational structural design translates into improved activity, selectivity, and substrate scope. Particular attention is devoted to guanidine-, DABCO-, and DBU-based ionic liquids, where mechanistic studies reveal cooperative activation modes rather than simple acid–base catalysis. Recent advances in supported and polymeric ionic liquids are also reviewed, demonstrating effective strategies to combine IL-like reactivity with enhanced recyclability and operational simplicity. Overall, this review clarifies the diverse roles of ionic liquids in aza-Michael chemistry and outlines current challenges and future perspectives toward more sustainable and efficient C–N bond-forming methodologies. Full article

The synthesis of enantiomerically pure chiral β-nitroalcohols is a crucial objective in asymmetric catalysis. In order to efficiently obtain such chiral products, we developed a series of thermoresponsive, oxazoline–copper catalysts (Cu^II-PN_xFe_yO_z) via sequential reversible addition–fragmentation chain transfer (RAFT) polymerization. These catalysts can self-assemble in water into single-chain nanoparticles (SCNPs) with biomimetic behavior, in which intramolecular hydrophobic and metal-coordination interactions generate a confined hydrophobic cavity. Comprehensive characterization by FT-IR, TEM, DLS, CD, CA, and ICP analysis confirmed the nanostructure and composition. When applied to the aqueous-phase asymmetric Henry reaction between nitromethane and 4-nitrobenzaldehyde, the optimal catalyst (2.0 mol%) achieved a quantitative yield (96%) with excellent enantioselectivity (up to 99%) within 12 h. Furthermore, the thermosensitive poly(N-isopropylacrylamide, NIPAAm) block enabled facile catalyst recovery through temperature-induced precipitation above its lower critical solution temperature (LCST). This work presents an efficient and recyclable biomimetic catalytic system, offering a novel strategy for designing sustainable chiral catalysts for green organic synthesis. Full article

The industrial preparation via solid-state polymerization (SSP) of high-viscosity copolyamides 6/66 (PA6/66) addresses the challenges, including prolonged reaction times, high energy consumption, and uneven viscosity distribution. In this study, sodium hypophosphite was introduced into the PA6/66 copolymerization system as a solid-state polymerization catalyst. The effects of this catalyst on the solid-state viscosity-increasing rate and relative viscosity were systematically investigated, and the extraction process was optimized to solve the loss of catalyst and controllable extractable content. The results showed that the relative viscosity of PA6/66 increased linearly with the SSP time, and the apparent viscosity increase rate could be stably maintained at 0.14 h⁻¹ at 160 °C due to the catalytic action. Based on the phosphorus (P) content in the chips, the viscosity increase rate is not further large when the P content is 25 ppm at 150 °C and 30 ppm at 160 °C, which can be added as a “control concentration” as a catalyst. The extraction kinetics showed that the catalyst concentration of the chip could be kept higher than the control concentration, and the extractable content can satisfy the requirements for processing. The catalyst of sodium hypophosphite was utilized on the 4500 tons/year PA6/66 continuous polymerization test line, and the high-viscosity PA6/66 chips with uniform viscosity were stably prepared. This study provides a reliable theoretical basis and process route for the large-scale continuous preparation of high-quality and high-viscosity PA6/66 resin. Full article