Undesired Polymerization Research Articles

Combine calculation and experiment to study the undesired polymerization of styrene for screening of effective inhibitors

Regarding undeniable formation of the undesired polymer (UP) in the styrene purification process, it is of vital importance to inhibit its production. To address the mentioned issue, effects of injecting antipolymers (e.g., stable nitroxide radicals (i.e., SNRs) and antioxidants (e.g., alkylhydroxylamines (AHA)) on the controlling the UP formation have been studied through density functional theory (DFT) calculations as well as experimental method in this study. In fact, electrophilicity and growth percentage were evaluated by DFT calculations and experimental approach, correspondingly. Accordingly, it was revealed that the best antipolymers in terms of inhibiting performance were 4‑hydroxy-2,2,6,6-tetramethyl piperidine 1-Oxyl (4‑hydroxy-TEMPO) and 4-oxo-2,2,6,6-tetramethylpiperidine 1-Oxyl (4-oxo-TEMPO), and from the antioxidants, N-Ethyl-N-phenyl hydroxylamine (EPHA) and N-Benzyl-N-phenyl hydroxylamine (BPHA) exhibited the best performance. In addition, the growth percentage of 18.70, 20.55, 24.85 and 46.8, were obtained for the EPHA, BPHA, 4‑hydroxy-TEMPO, and 4-oxo-TEMPO after 4 hrs of operation, correspondingly. Besides, the synergetic effects of the used inhibitors were determined experimentally. Among the evaluated inhibitors, EPHA/4‑hydroxy-TEMPO demonstrated the best synergetic effects over the control of UP formation. Finally, the blend of 4‑hydroxy-TEMPO (40 wt.%) and EPHA (60 wt.%) was obtained to be the optimum (best) inhibitor with 7.2 % polymer growth after 4 hrs of operation.

Study on H3PO4-activated carbon catalytic co-pyrolysis of bamboo and LDPE to poly-generation syngas and aromatics at low temperature

Biomass-derived carbon activated by H3PO4 was adopted to catalytic co-pyrolysis of bamboo and low-density polyethylene (LDPE) to produce syngas and aromatics on a fixed bed reactor. Effects of LDPE ratio in the feedstock, catalytic co-pyrolysis temperature and ratio of catalyst to feedstock on the yields and compositions of the products were investigated. The increase of LDPE ratio in liquid first improved and then reduced the relative content of aromatics, while it showed a positive effect on the yield and the H2/CO ratio of gas. 500℃ was an optimum temperature, under which the relative content of aromatics in liquid kept higher, meanwhile, avoided the undesirable polymerization reactions of monocyclic aromatics. At the same time, the content of H2 in gas reached a maximum (59.3%), which was in favor of poly-generation. H3PO4-activated carbon catalyst (H3PO4-ACC) with abundant functional groups on surface catalyzed cracking, hydrodeoxygenation, cyclization and aromatization reactions so as to facilitate the generation of aromatics. Non-condensable gas was dry reformed on P-ACC at the expense of CO2, CH4 and CO to generate char and H2. When the reaction condition was at a LDPE ratio of 50%, a catalyst/feedstock ratio of 2:1 and at 500℃, the relative content of aromatics in liqiud was 81.65% and the proportion of syngas component in gas was 79.73%. The volume ratio of H2/CO approached to 3:1 in gas under this condition. H3PO4-ACC catalytic co-pyrolysis of bamboo and LDPE could obtain high quality gas and liquid products at a relative low reaction temperature, which provided a new research idea on high-value application of biomass and waste plastics.

Ynamide Coupling Reagents: Origin and Advances.

Since the pioneering work of Curtius and Fischer, chemical peptide synthesis has witnessed a century's development and evolved into a routine technology. However, it is far from perfect. In particular, it is challenged by sustainable development because the state-of-the-art of peptide synthesis heavily relies on legacy reagents and technologies developed before the establishment of green chemistry. Over the past three decades, a broad range of efforts have been made for greening peptide synthesis, among which peptide synthesis using unprotected amino acid represents an ideal and promising strategy because it does not require protection and deprotection steps. Unfortunately, C → N peptide synthesis employing unprotected amino acids has been plagued by undesired polymerization, while N → C inverse peptide synthesis with unprotected amino acids is retarded by severe racemization/epimerization owing to the iterative activation and aminolysis of high racemization/epimerization susceptible peptidyl acids. Consequently, there is an urgent need to develop innovative coupling reagents and strategies with novel mechanisms that can address the long-standing notorious racemization/epimerization issue of peptide synthesis.This Account will describe our efforts in discovery of ynamide coupling reagents and their application in greening peptide synthesis. Over an eight-year journey, ynamide coupling reagents have evolved into a class of general coupling reagents for both amide and ester bond formation. In particular, the superiority of ynamide coupling reagents in suppressing racemization/epimerization enabled them to be effective for peptide fragment condensation, and head-to-tail cyclization, as well as precise incorporation of thioamide substitutions into peptide backbones. The first practical inverse peptide synthesis using unprotected amino acids was successfully accomplished by harnessing such features and taking advantage of a transient protection strategy. Ynamide coupling reagent-mediated ester bond formation enabled efficient intermolecular esterification and macrolactonization with preservation of α-chirality and the configuration of the conjugated α,β-C-C double bond. To make ynamide coupling reagents readily available with reasonable cost and convenience, we have developed a scalable one-step synthetic method from cheap starting materials. Furthermore, a water-removable ynamide coupling reagent was developed, offering a column-free purification of the target coupling product. In addition, the recycle of ynamide coupling reagent was accomplished, thereby paving the way for their sustainable industrial application.As such, this Account presents the whole story of the origin, mechanistic insights, preparation, synthetic applications, and recycle of ynamide coupling reagents with a perspective that highlights their future impact on peptide synthesis.

Investigation of physical, chemical and mechanical behaviour of nano-ZrO2-based dental composite

The incorporation of glass fibre in dental composite improves mechanical properties but doesn’t improves physical and chemical properties. Hence, in this paper, it has attempted to investigate the effect of nano-ZrO2 with varying content (0, 3, 6 and 9 weight percentage) on physical properties (water sorption behaviour, solubility), chemical properties (degree of conversion, polymerization shrinkage) as well as mechanical properties (compressive strength, flexural strength). The finding of the result indicated that polymerization shrinkage was decreased with the addition of nano-ZrO2. However, water sorption indicated varying trends in which it initially increased at 6 wt.% and later decreased at 9 wt.% nano-ZrO2. On the other hand, mechanical properties such as flexural strength and compressive strength were increased by 28.5% and 27.2%, respectively with the addition of 3 wt.% of nano-ZrO2 despite an increase in water sorption at 3 wt.% of nano-ZrO2 by 31%. Therefore, it can be concluded that the hygroscopic compensation due to water sorption in nano-ZrO2-based dental composite relieves the undesirable polymerization shrinkage but on the other side, the extensive amount of water sorption of nano-ZrO2-based dental composite results in degradation, softening, colour instability and decrease in mechanical properties.

Promoting productive metathesis pathway and tuning activity of multidentate molybdenum catalysts in alkyne metathesis: A theoretical perspective

Molybdenum alkylidyne complexes, including those containing monodentate or multidentate ligands, can catalyze CC bond formation via alkyne metathesis, which is of great importance to organic synthesis and materials chemistry. Herein, to understand the catalyst working mechanism and explore the key parameters determining the catalyst performance, alkyne metathesis catalyzed by molybdenum-based multidentate complexes was systematically investigated using density functional theory calculations. By comparing the desired cross metathesis and undesired polymerization pathways in multidentate and monodentate catalytic systems, the former shows significantly higher activation barrier for alkyne polymerization, resulting in the shutdown of ring-expansion by-product formation. Furthermore, the calculations show that the multidentate ligands taking trigonal-pyramidal geometry play two roles: (1) occupying one of substrate coordination sites to inhibit the polymerization pathway, thus promoting the desired productive pathway; (2) changing the electronic and steric environment to tune catalytic activity. It is worth noting that the metallacyclobutadiene complex with hither plane feature may play a key role in determining the activity of the catalysts. This work thus provides a guiding principle toward high-performance multidentate catalysts for alkyne metathesis.

3D printed dental protheses using TPO-initiated photopolymerization. Effect of the photoinitiator concentration and the use of a UV-blocker

ABSTRACT A DLP 3D printer was used to reproduce several objects (a trunk scaffold, a cube, and a dental crown) in order to ascertain the conditions to obtain the best resolution. The polymerizing solution was a mixture of BisGMA, TEGDMA, and UDMA monomers. The photoinitiator was triphenyl phosphinic oxide (TPO) at various concentrations in the presence and absence of the UV-light blocker 2.5-bis (5’-tert-butyl 2-benzoxazolyl)thiophene (Datilux OB). The printed objects were analyzed by Scanning Electron Microscopy. It was found that the best results were obtained using concentrations of 1 and 2% m/m of TPO in the presence of 0.1% of the UV-blocker. This blocker has an absorption spectrum similar to the photoinitiator and avoids secondary photoinitiations due to reflections that may cause imperfections in the printed objects. The effect of the UV-blocker was evaluated by thermal analysis of the obtained polymers showing that in the presence of the blocker 3–4 times more monomers remained unpolymerized, indicating that the more irregular objects were due to the excess of undesired polymerization. ShoreD hardness of the dental crown material was around 80, within the values reported for other dental materials.

MICRO-LEAKAGE OF PREHEATED COMPOSITE AS A CEMENTATION MATERIAL IN INDIRECT ADHESIVE RESTORATION (LITERATURE REVIEW)

Introduction: Composite resin is a material that is often used to perform dental restorations, but it can cause a deficiency called polymerization shrinkage which can be overcome by preheating the composite material. In several studies, there are differences of opinion regarding using preheating techniques at 60oC to overcome polymerization shrinkage. Review: This article intends to analyze the level of microleakage on the restoration of adhesive indirectly as cementing materials with preheated composites. A total of 49 journals from PubMed, NCBI, BMC, Research gate, Z-library, EBSCO, Google Scholar, and other international journal websites were analyzed. Conclusion: The preheating method showed samples with heating of 60oC had statistically lower microleakage at cervical margins. However, preheating resulted in an increase in the contraction voltage of undesirable polymerization.

FeBr3-catalyzed Fully Intermolecular [2+2+2] Cycloaddition of Alkenes

A methodology for the synthesis of cyclohexane scaffolds has been developed. The unprecedented fully intermolecular [2+2+2] cycloaddition reaction of three alkenes was catalyzed by an iron(III)-based Lewis acid to give multi-substituted cyclohexane products in a diastereoselective manner. The ionic species [FeBr2]+[FeBr4]− generated via disproportionation of FeBr3 is crucial for this catalysis: the strong Lewis acidity of [FeBr2]+ facilitates the addition reaction of alkenes, and [FeBr4]− controls the reaction path suppressing the undesired polymerization reaction by forming a dormant-like intermediate. This protocol offers a new synthetic way to obtain cyclohexane cycloadduct.

A Theoretical and Experimental Study for Screening Inhibitors for Styrene Polymerization

Styrene is one of the most important monomers utilized in the synthesis of various polymers. Nevertheless, during distillation, storage, and transportation of ST, undesired polymer (i.e., UP) formation can take place. Thus, the control of undesired polymerization of styrene is a challenging issue facing industry. To tackle the mentioned issue, the antipolymer and antioxidant activity of stable nitroxide radicals (i.e., SNRs) and phenolics in styrene polymerization were studied by density functional theory (DFT) calculation and experimental approach. The electrophilicity index and growth percentage have been determined by DFT calculation and experimental approach, respectively. It is depicted that 2,6-di-tert-butyl-4-methoxyphenol (DTBMP) and 2,6-di-tert-butyl-4-methylphenol (BHT) from phenolics, and 4-hydroxy-2,2,6,6-tetramethyl piperidine 1-Oxyl (4-hydroxy-TEMPO) and 4-oxo-2,2,6,6-tetramethylpiperidine 1-Oxyl (4-oxo-TEMPO) from stable nitroxide radicals were the most effective inhibitors. Also, the growth percentage of DTMBP, BHT, 4-hydroxy-TEMPO, and 4-oxo-TEMPO after 4 h were 16.40, 42.50, 24.85, and 46.8, respectively. In addition, the conversion percentage of DTMBP, BHT, 4-hydroxy-TEMPO, and 4-oxo-TEMPO after 4 h were obtained to be 0.048, 0.111, 0.065, and 0.134, respectively. Furthermore, the synergistic effect of these inhibitors was investigated experimentally, indicating that DTMBP/4-hydroxy-TEMPO exerted the best synergistic effects on the inhibition of polymerization. The optimum inhibition effect was observed at the blend of 4-hydroxy-TEMPO (25 wt.%) and DTMBP (75 wt.%) corresponding to 6.8% polymer growth after 4 h.

Phenol-functionalized polymerization control additives for negative tone epoxide crosslinking molecular resists

Controlling undesired polymerization in nominally unexposed regions is critical to achieving high-resolution, defect-free patterns when using negative tone molecular resists based on the crosslinking of epoxides. Two onium salt additives, a photodecomposable nucleophile (PDN) and a photoacid generator (PAG), were functionalized with phenols in order to investigate their use as generalized additives capable of slowing crosslinking and improving the resolution of a variety of epoxide resists. Presented here is a phenol-functionalized PDN [tris(4-hydroxyphenyl)sulfonium triflate (TPS-OH-Tf)] and a phenol-functionalized PAG [tris(4-hydroxyphenyl)sulfonium antimonate (TPS-OH-SbF6)] used in combination with a model epoxide resist (4-Ep). Utilizing additives that contained phenols resulted in a decrease in resist sensitivity, but enabled higher additive loadings which could be used to offset this loss in sensitivity. Using TPS-OH-SbF6 did not provide enough polymerization control to prevent line broadening, and the use of TPS-OH-Tf was still required to achieve sub 35 nm 1:1 line:space patterns. Adding TPS-OH-Tf was also found to improve pattern collapse behavior at reduced (<25 nm) feature sizes. Initial patterning using 100 keV electron-beam lithography showed that the resolution of 4-Ep was improved to 15 nm 1:1 line:space patterns using these phenol-functionalized additives and demonstrate the potential of these additives to improve the resolution of a variety of epoxide crosslinking molecular resists.

Superior Cascade Ring-Opening/Ring-Closing Metathesis Polymerization and Multiple Olefin Metathesis Polymerization: Enhancing the Driving Force for Successful Polymerization of Challenging Monomers.

Recently, our group successfully developed two new polymerization methodologies for monomers containing two cycloalkene moieties. These polymerization methods yielded well-defined polymers via a combination of ring-opening and ring-closing metathesis (cascade polymerization) or ring-opening, ring-closing, and cross-metathesis (multiple olefin metathesis polymerization (MOMP)) using a second monomer. However, cascade polymerization had some limitations such as low polymerization efficiency (maximum turnover number (TON) of 250) and narrow monomer scope. Furthermore, one-shot MOMP also showed a very narrow monomer scope because of certain undesired side reactions. To overcome these problems, we designed various new monomers containing cyclopentene and even more challenging ring-strain-free cyclohexene moieties, so that polymerization would produce a thermodynamically favored six-membered-ring backbone repeat unit. With this enhanced driving force for polymerization, these new monomers successfully underwent cascade polymerization with a high polymerization efficiency, leading to a maximum TON of 1940 and maximum number-average molecular weight ( Mn) of 343 kDa. Lastly, one-shot MOMP, which uses all three types of metathesis transformations in a single step, was possible with these monomers and gave highly A,B-alternating copolymers with high selectivity as well. This was possible because the newly designed monomers with the appropriate thermodynamic and kinetic preferences suppressed undesired polymerization pathways and reduced defects in the polymer microstructures. In short, we present our strategies for achieving superior cascade polymerization and MOMP using these new monomers.

Influence of substitution of various functional groups on inhibition efficiency of TEMPO analogues on styrene polymerization

Vinyl monomers such as styrene may undergo undesired polymerization reactions during the industrial processes in which they are synthesized and purified. To avoid this undesired phenomenon, polymerization inhibitors such as (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO) and its analogues can be used. An inhibitor and stability screening setup built in-house was used to compare the effectiveness of thirteen TEMPO analogues in inhibiting the polymerization of styrene in toluene at 130 °C. The data show that the substituent in the 4′-position in the cyclic structure of the TEMPO molecules strongly influenced their effectiveness in inhibiting polymerization. Computational methods based on the density functional theory (DFT) approach have been utilized to understand the reactivity of the TEMPO analogues. The global reactivity descriptors derived from the DFT calculations indicate that the TEMPO analogues with high global electrophilicity are more effective than those with low global electrophilicity in inhibiting the polymerization. The data suggest that the solubility of the TEMPO analogues in toluene and the keto–enol tautomerism of certain molecules may also affect their ability to inhibit styrene polymerization.

High-Performance thermal polymerization inhibitors based on 4-tert-Butylcatechol and its compositions for petrochemical plants

tert-Butylcatechol (TBC) has been tested under laboratory conditions as an inhibitor of undesired polymerization during the processing of liquid pyrolysis products and has shown high efficiency. Pilot- and industrial-scale tests and evaluation of TBC as an inhibitor in the thermal treatment of styrene have been carried out. It has been shown that this inhibitor operates only in a composition with other co-inhibitors. An inhibitory composition of TBC and copper diethyldithiocarbamate is proposed, which has shown high performance in the thermal treatment of both pyrolysis condensates and styrene. Other TBC formulations with monohydric sterically hindered phenols have been considered.

Valorization of food waste into hydroxymethylfurfural: Dual role of metal ions in successive conversion steps

This study aimed to transform food waste into a value-added chemical, hydroxymethylfurfural (HMF), and unravel the tangled effects induced by the metal catalysts on each single step of the successive conversion pathway. The results showed that using cooked rice and bread crust as surrogates of starch-rich food waste, yields of 8.1–9.5% HMF and 44.2–64.8% glucose were achieved over SnCl4 catalyst. Protons released from metal hydrolysis and acidic by-products rendered Brønsted acidity to catalyze fructose dehydration and hydrolysis of glycosidic bond. Lewis acid site of metals could facilitate both fructose dehydration and glucose isomerization via promoting the rate-limiting internal hydride shift, with the catalytic activity determined by its electronegativity, electron configuration, and charge density. Lewis acid site of a higher valence also enhanced hydrolysis of polysaccharide. However, the metals also catalyzed undesirable polymerization possibly by polarizing the carbonyl groups of sugars and derivatives, which should be minimized by process optimization.

Biocatalytic functionalization of hydroxyalkyl acrylates and phenoxyethanol via phosphorylation

The enzymatic phosphorylation of phenoxyethanol, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate catalyzed by acid phosphatases PhoN-Sf and PiACP at the expense of inorganic di-, tri-, hexameta- or polyphosphate was applied to the preparative-scale synthesis of phosphorylated compounds. The reaction conditions were optimized with respect to enzyme immobilization, substrate concentration, pH and type of phosphate donor. The mild reaction conditions prevented undesired polymerization and hydrolysis of the acrylate ester moiety. Application of a continuous flow system allowed facile scale-up and mono-phosphates were obtained in up to 26% isolated yield with space-time yields of 0.89kgL−1h−1.

Key Roles of Lewis Acid-Base Pairs on ZnxZryOz in Direct Ethanol/Acetone to Isobutene Conversion.

The effects of surface acidity on the cascade ethanol-to-isobutene conversion were studied using ZnxZryOz catalysts. The ethanol-to-isobutene reaction was found to be limited by the secondary reaction of the key intermediate, acetone, namely the acetone-to-isobutene reaction. Although the catalysts with coexisting Brønsted acidity could catalyze the rate-limiting acetone-to-isobutene reaction, the presence of Brønsted acidity is also detrimental. First, secondary isobutene isomerization is favored, producing a mixture of butene isomers. Second, undesired polymerization and coke formation prevail, leading to rapid catalyst deactivation. Most importantly, both steady-state and kinetic reaction studies as well as FTIR analysis of adsorbed acetone-d6 and D2O unambiguously showed that a highly active and selective nature of balanced Lewis acid-base pairs was masked by the coexisting Brønsted acidity in the aldolization and self-deoxygenation of acetone to isobutene. As a result, ZnxZryOz catalysts with only Lewis acid-base pairs were discovered, on which nearly a theoretical selectivity to isobutene (∼ 88.9%) was successfully achieved, which has never been reported before. Moreover, the absence of Brønsted acidity in such ZnxZryOz catalysts also eliminates the side isobutene isomerization and undesired polymerization/coke reactions, resulting in the production of high purity isobutene with significantly improved catalyst stability (<2% activity loss after 200 h time-on-stream). This work not only demonstrates a balanced Lewis acid-base pair for the highly active and selective cascade ethanol-to-isobutene reaction but also sheds light on the rational design of selective and robust acid-base catalyst for C-C coupling via aldolization reaction.

Formation of humin and alkyl levulinate in the acid-catalyzed conversion of biomass-derived furfuryl alcohol

To avoid undesired polymerization and maximize the selectivity of alkyl levulinate from the acid-catalyzed conversion of biomass-derived furfuryl alcohol, the effects of catalyst and reaction parameters on the formations of humin and alkyl levulinate were investigated. The results show that Amberlyst 15, of moderate acidic strength, was more favorable for the selective conversion of furfuryl alcohol to alkyl levulinate, and heteropolyacids of strong acidic strength tended to promote furfuryl alcohol polymerization. Compared with water as a reaction medium, alcohol significantly lowered humin formation and enhanced the yield of the resulting products. The formations of humin and alkyl levulinate were both favored at high catalyst loadings and reaction temperatures. An augmentation in initial furfuryl alcohol concentration caused an increase in humin formation and a decrease in alkyl levulinate yield. A high alkyl levulinate yield of up to 94% (100% furfuryl alcohol conversion) was achieved at 110 °C for 4 h with 5 g/L Amberlyst 15 catalyst and an initial furfuryl alcohol concentration of 0.1 mol/L. At this point, about 5% furfuryl alcohol was polymerized to form the humin, and its polymerization occurred mainly during the initial reaction stage.

Formation of Humin and Alkyl Levulinate in the Acid-catalyzed Conversion of Biomass-derived Furfuryl Alcohol

To avoid undesired polymerization and maximize the selectivity of alkyl levulinate from the acid-catalyzed conversion of biomass-derived furfuryl alcohol, the effects of catalyst and reaction parameters on the formations of humin and alkyl levulinate were investigated. The results show that Amberlyst 15, of moderate acidic strength, was more favorable for the selective conversion of furfuryl alcohol to alkyl levulinate, and heteropolyacids of strong acidic strength tended to promote furfuryl alcohol polymerization. Compared with water as a reaction medium, alcohol significantly lowered humin formation and enhanced the yield of the resulting products. The formations of humin and alkyl levulinate were both favored at high catalyst loadings and reaction temperatures. An augmentation in initial furfuryl alcohol concentration caused an increase in humin formation and a decrease in alkyl levulinate yield. A high alkyl levulinate yield of up to 94% (100% furfuryl alcohol conversion) was achieved at 110 °C for 4 h with 5 g/L Amberlyst 15 catalyst and an initial furfuryl alcohol concentration of 0.1 mol/L. At this point, about 5% furfuryl alcohol was polymerized to form the humin, and its polymerization occurred mainly during the initial reaction stage.

Effect of Water on Hydrolytic Cleavage of Non-Terminal α-Glycosidic Bonds in Cyclodextrins To Generate Monosaccharides and Their Derivatives in a Dimethyl Sulfoxide–Water Mixture

Hydrolytic cleavage of the non-terminal α-1,4-glycosidic bonds in α-, β-, and γ-cyclodextrins and the anomeric-terminal one in d-maltose was investigated to examine how the cleavage rate for α-, β-, and γ-cyclodextrins is slower than that for d-maltose. Effects of water and temperature were studied by applying in situ (13)C NMR spectroscopy and using a dimethyl sulfoxide (DMSO)-water mixture over a wide range of water mole fraction, xw = 0.004-1, at temperatures of 120-180 °C. The cleavage rate constant for the non-anomeric glycosidic bond was smaller by a factor of 6-10 than that of the anomeric-terminal one. The glycosidic-bond cleavage is significantly accelerated through the keto-enol tautomerization of the anomeric-terminal d-glucose unit into the d-fructose one. The smaller the size of the cyclodextrin, the easier the bond cleavage due to the ring strain. The remarkable enhancement in the cleavage rate with decreasing water content was observed for the cyclodextrins and d-maltose as well as d-cellobiose. This shows the important effect of the solitary water whose hydrogen bonding to other water molecules is prohibited by the presence of the organic dipolar aprotic solvent, DMSO, and which has more naked partial charges and higher reactivity. A high 5-hydroxymethyl-2-furaldehyde (5-HMF) yield of 64% was attained in a non-catalytic conversion by tuning the water content to xw = 0.30, at which the undesired polymerization by-paths can be most effectively suppressed. This study provides a step toward designing a new optimal, earth-benign generation process of 5-HMF starting from biomass.

Introducing A Podand Motif to Alkyne Metathesis Catalyst Design: A Highly Active Multidentate Molybdenum(VI) Catalyst that Resists Alkyne Polymerization

Podand prevents polymers: The molybdenum(VI) propylidyne catalyst 1 with a podand triphenolamine ligand shows high activity in the metathesis of a variety of alkyne substrates, including heterocycles that contain donor moieties. With one substrate-binding site blocked by the multidentate ligand, the undesired polymerization of small alkynes that occurs with non-podand-ligand complex 2 is completely inhibited.