Synthesis of poly(ethylene terephthalate) in benzyl imidazolium ionic liquids

Probing the Reversible Binding of Anionic Reactive Sulfur and Nitrogen Species in Imidazolium Receptors with Directional C-H Hydrogen Bonds

H2S and NO are physiologically important signaling molecules with complex roles in biology and intermolecular crosstalk. Although these species are often referred to as neutral on paper, they are primarily found in anionic and/or oxidized forms in aerobic solutions as HS- or NO2-/NO3-, respectively. Despite the prominence of these anions in biology, particularly HS- and NO2-, few investigations have focused on the molecular recognition and reversible binding of these important species. Using a library of imidazolium receptors with C-H hydrogen bonding interactions, we investigate the influences on binding affinity through modulation of charge, multiplicity, and preorganization, while also investigating how anion volume impacts binding. These factors are probed by solution-state titration experiments and solid-state X-ray crystallographic data showing the specific molecular interactions involved in guest binding. Both solution-state NMR and solid-state X-ray crystallography support the importance and abundance of C-H···X- interactions in facilitating guest binding as well as conformational changes upon anion recognition.

Mechanistic insight into the roles of anions and cations in the degradation of poly(ethylene terephthalate) catalyzed by ionic liquids

Ionic liquids (ILs) have shown high catalytic activity in the degradation of poly(ethylene terephthalate) (PET), but the effects of the anions and cations, as well as the mechanism, remain ambiguous. Glycolysis is an important recycling method that converts waste PET into monomers through various chemical reactions. To reveal the role of ILs and the molecular mechanism of the glycolysis of PET, density functional theory (DFT) calculations have been carried out for the possible pathways for the generation of bis(hydroxyethyl)terephthalate (BHET) catalyzed by isolated anions/cations and ion pairs at different sites. The pathway with the lowest barrier for the glycolysis of PET is the cleavage of the C-O ester bond, which generates the BHET monomer. The synergistic effects of the cations and anions play a critical role in the glycolysis of PET. The cations mainly attack the carbonyl oxygen of PET to catalyze the reaction, and the anions mainly form strong H-bonds with PET and ethylene glycol (EG). In terms of the mechanism, the H-bonds render the hydroxyl oxygen of EG more electronegative. The cation coordinates the carbonyl oxygen of the ester, and the hydroxyl oxygen of EG attacks the ester group carbon of PET, with proton transfer to the carbonyl oxygen. A four-membered-ring transition state would be formed by PET, EG, and the IL catalyst, which regularly accelerates the degradation of PET. These results provide fundamental help in understanding the roles of ILs and the mechanism of IL-catalyzed PET degradation.

A Brønsted Acidic Ionic Liquid as an Efficient and Selective Catalyst System for Bioderived High Molecular Weight Poly(ethylene 2,5-furandicarboxylate)

Green synthesis of bioderived high-molecular-weight poly(ethylene 2,5-furandicarboxylate) (PEF) over metal-free catalysts is a significant challenge. This study focuses on PEF prepared from ethylene glycol and 2,5-furandicarboxylic acid (FDCA) through a direct esterification method with ecofriendly metal-free ionic liquids (ILs) as catalysts. The catalytic activities of a series of imidazolium cations in the presence of various anions are systematically investigated and found to be mainly governed by the anions. Among the ILs studied, 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂ MIM]BF₄ ) is identified as the best catalyst, showing excellent catalytic activity, selectivity, and stability, even at low catalyst loadings (0.1 mol % w.r.t. FDCA). Optimization of the polymerization parameters enables [C₂ MIM]BF₄ -catalyzed production of PEF with a high number-average molecular weight (M_n =5.25×10⁴  g mol^-1 ). The relationship between Brønsted acidity and catalytic activity is also investigated and the results show that the trend in catalytic activity is in good agreement with that in Brønsted acidity, as determined by the Hammett method. Additionally, on the basis of experimental results and density functional theory calculations, an electrophilic activation mechanism induced by hydrogen bonds is proposed. This strategy of adjustable acidity and anion structure in ILs provides an opportunity to develop other ILs for bio-based polyesters through green synthesis pathways.

Effect of water and methanol on the dissolution and gelatinization of corn starch in [MMIM][(MeO)HPO2]

A small proportion of water or methanol in the complex solvents of IL ([MMIM][(MeO)HPO₂])/water and IL ([MMIM][(MeO)HPO₂])/water/methanol, respectively, could significantly accelerate the gelatinization/dissolution of corn starch.

Thermal-sensitive Starch-g-PNIPAM prepared by Cu(0) catalyzed SET-LRP at molecular level

Starch-g-PNIPAM with controlled graft chains and its hydrogels with rapid shrinking rate were preparedviaSET-LRP at molecular level.