Inside Cover: Mechanistic Understanding of Efficient Polyethylene Hydrocracking over Two-Dimensional Platinum-Anchored Tungsten Trioxide (Angew. Chem. Int. Ed. 40/2023)

Chemical upcycling of polyethylene (PE) can convert plastic waste into valuable resources. However, engineering a catalyst that allows PE decomposition at low temperatures with high activity remains a significant challenge. Herein, we anchored 0.2 wt.% platinum (Pt) on defective two-dimensional tungsten trioxide (2D WO₃) nanosheets and achieved hydrocracking of high-density polyethylene (HDPE) waste at 200–250 °C with a liquid fuel (C_5–18) formation rate up to 1456 g_products ⋅ g_{metal species}⁻¹ ⋅ h⁻¹. The reaction pathway over the bifunctional 2D Pt/WO₃ is elucidated by quasi-operando transmission infrared spectroscopy, where (I) well-dispersed Pt immobilized on 2D WO₃ nanosheets trigger the dissociation of hydrogen; (II) adsorption of PE and activation of C−C cleavage on WO₃ are through the formation of C=O/C=C intermediates; (III) intermediates are converted to alkane products by the dissociated H. Our study directly illustrates the synergistic role of bifunctional Pt/WO₃ catalyst in the hydrocracking of HDPE, paving the way for the development of high-performance catalysts with optimized chemical and morphological properties.     

Solvent-Free Heterogeneous Catalytic Hydrogenation of Polyesters to Diols

The utilization of carbon resources stored in plastic polymers through chemical recycling and upcycling is a promising approach for mitigating plastic waste. However, most current methods for upcycling suffer from limited selectivity towards a specific valuable product, particularly when attempting full conversion of the plastic. We present a highly selective reaction route for transforming polylactic acid (PLA) into 1,2-propanediol utilizing a Zn-modified Cu catalyst. This reaction exhibits excellent reactivity (0.65 g g_cat⁻¹ h⁻¹) and selectivity (99.5 %) towards 1,2-propanediol, and most importantly, can be performed in a solvent-free mode. Significantly, the overall solvent-free reaction is an atom-economical reaction with all the atoms in reactants (PLA and H₂) fixed into the final product (1,2-propanediol), eliminating the need for a separation process. This method provides an innovative and economically viable solution for upgrading polyesters to produce high-purity products under mild conditions with optimal atom utilization.     

Thermal properties of poly(alkylene dicarboxylate)s derived from 1,12‐dodecanedioic acid and even aliphatic diols

A series of new aliphatic polyesters derived from 1,12‐dodecanedioic acid and different diols with an even number of methylene units have been studied to assess the effect of the chemical structure on the final thermal properties of the materials. The polyesters have high thermal stability and are fast crystallizing polymers, with crystallization rate similar to that of polyethylene (PE). This behavior is connected to the fact that long aliphatic chains assume conformational characteristics very similar to that of PE. However, the polyester prepared from ethanediol shows a peculiar behavior (for example, double melting peak, melting and crystallization temperatures, which do not fit the trend of those of the other samples and ringed spherulites) owing to a probable different conformation, deviating from the all‐trans planar typical of PE. In the isothermal crystallization studies, a bell‐shape trend has been found for the crystallization rate as a function of the number of ? (CH₂)? units in the diol. The high crystallization rate of the sample with long ? (CH₂)? sequences has been attributed to the high chain flexibility and, thus, high mobility in the molten state and ease of chain folding. By reducing the aliphatic sequence length, instead, implications of the structural characteristics of the samples are probably involved. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1053–1067, 2007     

Hardness of nitric acid treated polyethylene followed by recrystallization

The hardness variation of melt crystallized polyethylene as a consequence of controlled fuming nitric exposure has been investigated using the microindentation technique. This study complements previous results obtained using other reagents (H₂SO₄, ClHSO₃). After HNO₃ exposure the microhardness of polyethylene decreases very rapidly, instead of increasing after the first hours of treatment. The hardness decrease is correlated to the volume fraction of interlamellar microvoids arising through selective acid digestion. For longer treatment times (t>40 h) the fragility of the material increases and the sample collapses under the indenter. The hardening of the degraded material after recrystallization from the melt is followed as a function of treatment time. The results are discussed in the light of the molecular mechanisms involved. Comparison of the experimental data with hardness calculations for ideal PE lamellar structures and chain extended dicarboxylic crystals implies that the major contribution to hardening is due to electron dense groups attachment at the surface of a mixed lamellar structure.     

Broad line NMR studies of linear and branched polyethylene

Temperature dependence of the shape and linewidth of the broad-line NMR spectra of commercially available high-density polyethylene (PE/HD), low-density polyethylene (PE/LD with ～3 per cent CH₃), block-copolythene (PE/AA with ～3 per cent acrylic acid) and polyethylene single crystal (PE/SC) were investigated to obtain information on the effect of branching and structural changes on the glass-transition temperature (Tg) and activation energy of molecular motion (E). The relatively lower value of Tg ～- ?100° for PE/HD compared to Tg ～- ?85° and ?60° for PE/CH₃ and PE/AA, along with the estimated lower value of E ～- 2·1 kcal/mole for PE/HD compared to 2·6 and 5·1 kcal/mole for PE/CH₃ and PE/AA, respectively, were interpreted by a molecular reorientational process connected mainly with the sidegroups of the main polymeric chains.     

Chain Multiplication of Fatty Acids to Precise Telechelic Polyethylene

Starting from common monounsaturated fatty acids, a strategy is revealed that provides ultra‐long aliphatic α,ω‐difunctional building blocks by a sequence of two scalable catalytic steps that virtually double the chain length of the starting materials. The central double bond of the α,ω‐dicarboxylic fatty acid self‐metathesis products is shifted selectively to the statistically much‐disfavored α,β‐position in a catalytic dynamic isomerizing crystallization approach. “Chain doubling” by a subsequent catalytic olefin metathesis step, which overcomes the low reactivity of this substrates by using waste internal olefins as recyclable co‐reagents, yields ultra‐long‐chain α,ω‐difunctional building blocks of a precise chain length, as demonstrated up to a C₄₈ chain. The unique nature of these structures is reflected by unrivaled melting points (T _m=120 °C) of aliphatic polyesters generated from these telechelic monomers, and by their self‐assembly to polyethylene‐like single crystals.     

Preparation and chain extension of C100dicarboxylic acid

The selective degradation of polyethylene crystals with fuming nitric acid has been used to prepare a C₁₀₀ chain with terminal functional groups. After treating this product with concentrated sulphuric acid, it is shown by average molecular weight, titration and infra-red spectroscopy measurements that each molecule contains two carboxylic acid groups. This C₁₀₀ dicarboxylic acid is chain extended with several low molecular weight difunctional coupling agents. Block copolymers of this acid and poly(propylene glycol) have been prepared.     

One‐Step Synthesis of Collagen Hybrid Gold Nanoparticles and Formation on Egyptian‐like Gold‐Plated Archaeological Ivory

A one‐step method is reported to synthesize hybrid gold nanoparticles (AuNPs) by reduction of HAuCl₄ in acetic solution in the presence of collagen (Col), dicarboxylic acid‐terminated polyethylene glycol (PEG), and cetyltetrammonium bromide (CTAB) mixed with hydoxyapatite (HAP) as surfactants. Such formation process of AuNPs was shown to be responsible for purple stains naturally formed on Egyptianizing archaeological gilded ivories from 8th BC Syria. The understanding of this formation mechanism, which most likely involves a step with hybrid AuNPs, allows the establishing of an authenticity marker of ancient gold‐plated ivories.     

Ultraviolet grafting of methacrylic acid and acrylic acid on high‐density polyethylene in different solvents and the wettability of grafted high‐density polyethylene. I. Grafting

Methacrylic acid (MAA) and acrylic acid (AA) were grafted onto high‐density polyethylene (PE) with UV initiation and a range of solvents. With acetone as the solvent, MAA was more easily grafted onto PE when the photoinitiator benzophenone was precoated on PE than when it was dissolved in the monomer solution. The grafting was faster in aliphatic solvents than in polar solvents or a UV‐adsorbing aromatic solvent (toluene). Acetone itself could initiate the photografting of both MAA and AA onto PE when it was mixed with water. The extent of grafting of MAA onto PE showed a maximum when there was about 40% acetone in the mixture. For AA, when the acetone/water concentration was 10%, the extent of grafting increased rapidly with the irradiation time. At higher acetone concentrations, the extent of grafting was low. Atomic force microscopy images showed that the surface topography of PE grafted with MAA in acetone/water was quite different from that obtained when the grafting was performed in other organic solvents. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 253–262, 2004     

Exploring rearrangements along the fragmentation of glutaric acid negative ion: a combined experimental and theoretical study

Glutaric acid, a common short‐chain aliphatic dicarboxylic acid, was investigated in the negative ion mode by subjecting its [M–H]^? ion to collision‐induced dissociation (CID) experiments in an infinity ion cyclotron resonance (ICR) cell coupled to a hexapole–quadrupole–hexapole ion guide. A 12 Tesla magnet was used for high‐resolution measurements. Two distinctive main pathways were observed in the MS/MS spectrum. The fragmentation pathways were also thoroughly investigated in a density functional theory (DFT) study involving a B3LYP/6‐311+G(2d,p)//B3LYP/6‐311+G(d,p) level of theory. Elimination of CO₂ from the [M–H]^? ion of the dicarboxylic acid takes place in a concerted mechanism, by which a 1,5 proton shift occurs from the intact carboxyl group to the methylene moiety located in the α position relative to the deprotonated carboxyl group. This concerted mechanism stabilizes the terminal negative charge and deprotonates the second carboxylic acid group. Water elimination from the [M–H]^? ion does not take place by means of a simple proton removal from the α methylene group – and OH^? release from the carboxylate group to abstract an additional α proton thus leading to the formation of a deprotonated ketene anion. In the case of this dicarboxylic acid, a new mechanism was found for water elimination, which differs from that known for aliphatic monocarboxylic acids. An intramolecular interaction between the deprotonated and the intact carboxyl groups plays a key role in making a new energetically favourable mechanism. The DFT study also reveals that a combined loss of CO₂ and H₂O in the form of H₂CO₃ is possible. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of the lithium cation on the sorption and electrical properties of amphiphilic block copolymers and their composites

The use of lithium cation in composites of block copolymers [polyethylene‐b‐polyethylene oxide (PE‐b‐50%PEO and PE‐b‐80%PEO)] and their derivatives was tested as a modifier of the vapor sorption and impedance of these complexes. The block copolymer PE‐b‐80%PEO was modified by oxidation of its hydroxyl end group to both a carboxylic acid group (PE‐b‐80%PEO)CH₂COOH and its sodium salt (PE‐b‐80%PEO)CH₂COO^? Na⁺ for the purpose of improving its compatibility and performance as a matrix for composites. These modified copolymers were characterized by FTIR, DSC, and mass spectrometry. The sorption of water of these copolymers and their composites with lithium nitrate was also compared, as well as the electrical properties of their composites were measured by electrical impedance spectroscopy. For the composites obtained with PE‐b‐80%PEO and lithium nitrate, it was found that lithium cation plays an important role increasing the sorption rate, which is maximized for the PE‐b‐80%PEO + (21% lithium nitrate) composite. For the copolymers (PE‐b‐80%PEO)CH₂COOH and (PE‐b‐80%PEO)CH₂COO^? Na⁺ and their composites, the highest sorption rate was observed for salt in the following order: COO^? Na⁺ > COOH > OH. The PE‐b‐80%PEO + (21% lithium nitrate) composite behaves as a solid polymeric ionic conductor fitting the Williams–Landel–Ferry equation. However, both (PE‐b‐80% PEO)CH₂COOH and (PE‐b‐80%PEO)CH₂COO^? Na⁺ + (21% lithium nitrate) composites fitted the Variable Range Hopping equation, indicating a conductance trend with temperature governed by a thermally activated with energy of 0.482 and 0.524 eV and not by a relaxation process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1809–1817, 2010     

Adsorption of UO2+2 by polyethylene adsorbents with amidoxime,carboxyl, and amidoxime/carboxyl group

The polyethylene (PE) adsorbents were prepared by a radiation-induced grafting of acrylonitrile (AN), acrylic acid (AA), and the mixture of AN/AA onto PE film, and by subsequent amidoximation of cyano groups of poly-AN graft chains. With an increase of AA composition in AN/AA monomer mixture, the water uptake of the grafted polyethylene film increased. In AN/AA mixture, the maximum adsorption of UO²⁺₂ was observed in the adsorbent with a ratio of AN/AA (50/50, mol%) in copolymer. The amidoxime, carboxyl, and amidoxime/carboxyl groups onto PE acted as a chelating site for the selected UO²⁺₂. The complex structure of polyethylene with three functional groups and UO²⁺₂ was confirmed by Fourier Transform Infrared (FTIR) spectroscopy.     

Microwave-mediated one step synthesis of tri- and tetracyclic heterocyclic molecules

Abstract

Tricyclic and tetracyclic compounds related to vasicine and batracyclin, respectively, have been synthesized via condensation of dicarboxylic acids (aliphatic acid, homophthalic acid, and aromatic acid) with diamines (aliphatic, aminobenzyl amine, and aromatic amine) under solvent-free condition.     

Protective encapsulation of acid‐sensitive catalysts using polyethylene ligands

The stability of polyethylene oligomer (PE_Olig)‐entrapped salen‐metal complexes toward acidolysis is described. These complexes dissolve in hot toluene and precipitate as hydrophobic powders. The salen species in these precipitates or in precipitates of admixtures of oligomeric complexes and unfunctionalized polyethylene are stable to acid when suspended in acidic methanol for 24 h at 25°C. The lack of metal leaching due to acid‐promoted demetalation was determined using both colorimetric and ICP‐MS analyses. The ICP‐MS results showed the amount of metal loss for PE_Olig‐salen‐metal complexes was 0.27%, 0.45%, and 0.79% for half‐salen Cr(III), salen Cr(III), and salen Mn(III) complexes, respectively. These results were in contrast to the reported behavior of low molecular weight salen metal complexes and to results seen with a salen complex bound to divinylbenzene (DVB) crosslinked polystyrene which demetalates under acidic conditions at room temperature. Salen complexes formed with PE_Olig complexes also demetalate when the PE_Olig‐bound species are in solution at elevated temperature and exposed to acid. These results show that as solids oligomeric polyethylene ligands even without added PE can serve as a protective encapsulating matrix for the solid forms of polymer‐supported catalysts. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Entropy Confinement Promotes Hydrogenolysis Activity for Polyethylene Upcycling

Chemical upcycling that catalyzes waste plastics back to high-purity chemicals holds great promise in end-of-life plastics valorization. One of the main challenges in this process is the thermodynamic limitations imposed by the high intrinsic entropy of polymer chains, which makes their adsorption on catalysts unfavorable and the transition state unstable. Here, we overcome this challenge by inducing the catalytic reaction inside mesoporous channels, which possess a strong confined ability to polymer chains, allowing for stabilization of the transition state. This approach involves the synthesis of p-Ru/SBA catalysts, in which Ru nanoparticles are uniformly distributed within the channels of an SBA-15 support, using a precise impregnation method. The unique design of the p-Ru/SBA catalyst has demonstrated significant improvements in catalytic performance for the conversion of polyethylene into high-value liquid fuels, particularly diesel. The catalyst achieved a high solid conversion rate of 1106 g ⋅ g_Ru⁻¹ ⋅ h⁻¹ at 230 °C. Comparatively, this catalytic activity is 4.9 times higher than that of a control catalyst, Ru/SiO₂, and 14.0 times higher than that of a commercial catalyst, Ru/C, at 240 °C. This remarkable catalytic activity opens up immense opportunities for the chemical upcycling of waste plastics.     

Regular Copolyamides. III. Preparation and Characterization of Regular Aliphatic/Aromatic Copolyoxamides

Regular aliphatic/aromatic copolyoxamides were prepared from diamine-oxamides and aromatic diacid chlorides by interfacial and solution polymerization. Solution polymerization in chloroform or dimethylacetamide is preferred for the preparation of large quantities of polymers but interfacial polymerization is most conveniently carried out for the preparation of polymers with high molecular weight. Aromatic diacid chlorides used included the diacid chlorides of terephthalic acid, isophthalic acid, 2,6-pyridinedicarboxylic acid, two isomeric naphthalene dicarboxylic acids, two cyclo-hexanedicarboxylic acid isomers, as well as 1,1-cyclobutane-dicarboxylic acid. Copolymers of diamine-oxamides with mixtures of acid chlorides of isophthalic and pyridine dicarboxylic acid and isophthalic acid/tetrachloroterephthalic acid have also been prepared. Most polymers are film-forming and are soluble in concentrated sulfuric acid, trifluoroacetic acid, and dimethylacetamide (containing several per cent LiCl). A number of these polymers gave dense or asymmetric membranes, particularly the polymers from ethylene diamine as the aliphatic diamine, particularly poly(iminoethyleneimino-oxalyliminoethyleneiminoisophthaloyl) (p-222I). Diamine oxamides with more than two amide groups in the molecules have been prepared, and in one case polymers with aromatic diacid chlorides have been prepared by interfacial polymerization. All regular aliphatic/aromatic copolyoxamides are high-melting and generally decompose above 350°C without melting. They can, however, be fabricated from solution into brittle fibers or into desalination membranes.     

Insights into coal structure from degradation with ruthenium tetroxide and tandem mass spectrometry

The products of ruthenium tetroxid oxidation of coal (Illinois No. 2) at ambient temperature were examined by tandem mass spectrometry using positive and negative chemical ionization. The negative-ion mass spectrum of the coal sample displays seven homologous series of ions. Individual compounds were characterized by recording daughter spectra. In this way, the following types of compounds were identified: aliphatic dicarboxylic acids, aromatic dicarboxylic and tricarboxylic acids, anhydrides of the di- and tri-carboxylic acids, and dianhydrides corresponding to the tetracarboxylic aromatic acids. The positive-ion mass and daughter spectra provided additional confirmation. Two series of ions dominate the positive-ion mass spectrum, those from the aliphatic dicarboxylic acids, and the corresponding anhydrides. The fragmentation behavior of model compounds was examined to confirm these assignments. The carboxylic acids and anhydrides identified suggest the presence of particular structural features in the coal prior to oxidation. These include C₂–C₆ aliphatic bridges between aromatic units, fused ring aromatic structures, tetralin and indan structures.     

Mathematical modeling of the graft reaction between polystyrene and polyethylene

Polystyrene (PS) and polyethylene (PE) are two major components of household plastic waste whose blends are immiscible. Recycling them together is an attractive option that requires a compatibilization process to improve the blend mechanical properties. If a PE/PS copolymer is added or formed in situ, it may act as compatibilizer. The structure and molecular properties of this copolymer are key factors to assure its effectivity as a compatibilizer. In this work, we study the graft copolymerization reaction between polystyrene and polyethylene using the catalytic system composed of AlCl₃ and styrene. We develop a model of this process which considers that PE/PS grafting and PS degradation occur simultaneously. We propose a kinetic mechanism for the whole process and apply the method of moments to solve the mass balance equations. The model is able to calculate average molecular weights as well as the amount of grafted PS. It accurately describes the available experimental data, constituting a valuable tool for simulation and optimization purposes.     

Vinyl Ethers with Isothiocyanate Group: XVIII.2* Reaction with Dicarboxylic Acids, an Easy Way to Bisacylals with Isothiocyanate Groups

Electrophilic reaction between 2-(vinyloxy)ethyl isothiocyanate and aliphatic and aromatic dicarboxylic acids (malonic, succinic, glutaric, sebacic, maleic, and phthalic) affords bisacylals with isothiocyanate groups in quantitative yield. The process is carried out at heating without solvent in the presence of catalytic quantities of trifluoroacetic acid.     

Development of a General and Efficient Iron‐Catalyzed Epoxidation with Hydrogen Peroxide as Oxidant

The development of inexpensive and practical iron catalysts for the environmentally benign epoxidation of olefins with hydrogen peroxide as terminal oxidant is described. By systematic variation of ligands, metal sources, and reaction conditions, it was discovered that FeCl₃?6H₂O in combination with pyridine‐2,6‐dicarboxylic acid and different amines shows high reactivity and excellent selectivity towards the epoxidation of aromatic olefins and moderate reactivity towards that of aliphatic olefins.