RESUMO
In this paper, a series of energetic ionic liquid plasticizers of 1-methyl-4-methoxyethyl-1,2,4-triazolium chloride (1), 1-methyl-4-methoxyethyl-1,2,4-triazolium bis(trifluoromethylsulfonyl)imide (1a), 1-methyl-4-methoxyethyl-1,2,4-triazolium nitrate (1b), 1-methyl-4-ethyl acetate-1,2,4-triazolium chloride (2), 1-methyl-4-ethyl acetate-1,2,4-triazolium bis(trifluoromethylsulfonyl)imide (2a), and 1-methyl-4-ethyl acetate-1,2,4-triazolium nitrate (2b) were synthesized and characterized. The results show that compounds 1a, 1b, 2a, and 2b have lower melting points (Tm, -72.60 to -32.67 °C) and good thermal stability (Td, 161-348 °C) and are suitable as plasticizers for hydroxyl-terminated polybutadiene (HTPB) curing systems. Among these four ionic liquids, ester-functionalized cations can help to improve the tensile strength (2a, 0.943 MPa; 2b, 1.113 MPa) of the cured system, while ether-functionalized cations are more beneficial to improve elongation at break (1a, 522.90%; 1b, 484.45%). Ester-functionalized ionic liquids are more beneficial to reduce the glass transition temperature of HTPB elastomers. The storage modulus of HTPB elastomers containing NO3- is higher, while that of HTPB elastomers containing NTf2- is lower. The crosslink densities of HTPB/TDI/2a and HTPB/TDI/2b plasticized by ester-functionalized ionic liquids are larger, which are 9369 and 9616 mol/m3, respectively. There are hydrogen bond interactions between the ionic liquid and the HTPB elastomer, and these interactions changed the distribution of the hard and soft segments in the polymer molecules.
RESUMO
Oxygenated fuel has the function of self-supplying oxygen during the combustion process, which can greatly improve emission performance and reduce diesel fuel soot production. In this paper, a novel oxygenated fuel poly(oxymethylene) dibutyl ether (PODBE n ) is designed and synthesized through experiments in combination with density functional theory (DFT) calculation. The experimental results show that PODBE n has the advantages of high cetane number (73.6), moderate density (868 kg/m3), and low condensation point (-72 °C). According to the DFT calculation results, the molecular (PODBE n ) polarity index of different polymerization degrees is similar to the value of diesel and has good mutual solubility with diesel. Moreover, the mechanism of the entire path of synthesis is calculated at the M06-2X/6-311G(d,p) level of theory. The energetic profile reveals that the rate-determining step is the nucleophilic addition step with the highest barrier energy (TS1 = 21.59 kcal/mol). This work provides a feasible method to synthesize high-performance oxygenated fuel PODBE n using NKC-9 ion-exchange resins.
RESUMO
Chemical fixation of CO2 is an efficient means for decreasing amount of CO2 in the atmosphere. One of promising technologies is the cycloaddition of CO2 with epoxides to synthesize cyclic carbonates. In this reaction, ionic liquid (IL) catalysts show versatile and unique advantages. However, the reaction mechanism using ILs is not clear. In this work, a detailed theoretical investigation was performed by DFT calculations. The energetic profile shows that the reaction consists of three steps, with the ring-opening step being the rate-determining step. Based on the results, effects of cations, anions and water were calculated. Cations show strong hydrogen bonding interactions with epoxides, which decreases the energy barrier of the ring-opening step, indicating that hydrogen bonds play a positive role in promoting the reaction. The effect of anions was evaluated by nucleophilicity index (NNu ); anions with a larger NNu (stronger nucleophilicity) value show lower energy barriers. The influence of water was investigated by implicit and explicit models. Compared with the solvent-free case, water as an implicit solvent decreases the energy barriers through polarization with epoxides. In the explicit solvent model, the water molecules form new hydrogen bonds with epoxides and cations, which can efficiently reduce the energy barriers. The result indicates that there is a new synergic catalytic mechanism, in which the water acts not only as solvent but also as a catalyst in the reaction. Supporting experiments further confirm the calculation results.
