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The synthesis of self-healing and recyclable polymeric materials from renewable CO2 is of great importance in the fields of functional materials and sustainable chemistry. In this work, mechanically robust poly(urea-imine) (PUI) thermosets were prepared from CO2-sourced oligourea (OUa), terephthalaldehyde (TA) and tri(2-aminoethyl)amine (TAEA) through condensation between equimolar amino and aldehyde groups. The synthesized PUIs have satisfactory mechanical performance, seal-healing and recyclable properties as they contain cross-linked dynamic imine bonds and reversible hydrogen bonds. These properties can be adjusted by changing the ratio of TAEA to OUa, thus varying the chemical bonds and chain structure. The highest values for the mechanical properties tensile stress (10.2 MPa) and Young's modulus (79 MPa) were obtained in a PUI thermoset synthesized from a molar ratio of TAEA to OUa of 3 : 2 (OUa2-T3). In addition, this thermoset can be healed at 80 °C with a healing efficiency over 92% owing to the high reversibility of imine and hydrogen bonds and the flexibility of CO2-sourced OUa chains. Moreover, it can also be reprocessed and recycled by physical and/or chemical means without change in its chemical structure, glass transition temperature and original mechanical properties. Additionally, this PUI thermoset can be easily degraded into its original reagents OUa, TA and TAEA under acid conditions. Therefore, as novel sustainable materials, the PUI thermosets reported in this article have great potential to replace conventional non-degradable thermosets over a wide field. [ABSTRACT FROM AUTHOR]

Using CO2 as a carbonyl building block to synthesize valuable chemicals is an important issue in the field of green and sustainable chemistry. Herein, the conversion of CO2 with glycerol to glycerol carbonate was investigated in the presence of 2-cyanopyridine. It was found that 2-cyanopyridine not only acts as the dehydrating agent to break the thermodynamic limit of the reaction, but also activates the carbonyl bond of CO2 to catalyze the present carbonylation as confirmed by FTIR experimental spectra. Moreover, the activation closely depends on the stereo-structure of cyanopyridine, in that 3-cyanopyridine and 4-cyanopyridine do not have such activating function. The theoretical calculation demonstrated that 2-cyanopyridine could bond CO2 through the conjugating nitrogen to form a five-membered ring, thus CO2 is activated and then reacts with glycerol to produce glycerol carbonate. The reaction parameters were examined and evaluated for the reaction catalyzed with 2-cyanopyridine in the absence of any metal catalysts and additives. With increasing CO2 pressure, the yield of glycerol carbonate increases, and under the optimum conditions an 18.7% yield is obtained which is one of the best results reported up to now. The present work provides a new way for activation of CO2. [ABSTRACT FROM AUTHOR]

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was studied with a homogeneous RuCl2(PPh3)3 catalyst in supercritical CO2 (scCO2). The conversion of LA was observed to increase with CO2 pressure and the possible reasons for this rate acceleration were discussed, including the molecular interactions of CO2 with the reacting and catalytic species as well as the acidity and phase behavior of the reaction mixture. The interaction between CO2 and RuCl2(PPh3)3 was significant, which resulted in the production of an active RuHCl(CO)(PPh3)3 complex and thus enhanced the rate of hydrogenation in the presence of CO2. [ABSTRACT FROM AUTHOR]

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was studied with a homogeneous RuCl2(PPh3)3 catalyst in supercritical CO2 (scCO2). The conversion of LA was observed to increase with CO2 pressure and the possible reasons for this rate acceleration were discussed, including the molecular interactions of CO2 with the reacting and catalytic species as well as the acidity and phase behavior of the reaction mixture. The interaction between CO2 and RuCl2(PPh3)3 was significant, which resulted in the production of an active RuHCl(CO)(PPh3)3 complex and thus enhanced the rate of hydrogenation in the presence of CO2. [ABSTRACT FROM AUTHOR]

Urea derivatives are obtained in mild to good yield from the reactions of primary aliphatic amines with CO2in the absence of any catalysts, organic solvents or other additives. To optimize reaction conditions, experimental variables including temperature, pressure, the concentration of amine, reaction time etc.were studied. Satisfactory yields were obtained at the optimized conditions that are comparable to the presence of catalyst and solvent. The preliminary investigation of the reaction mechanism showed that alkyl ammonium alkyl carbamate was quickly formed as the intermediate, and then the final product was formed by the intramolecular dehydration. [ABSTRACT FROM AUTHOR]

Chemoselective hydrogenation of water-insoluble aromatic nitro compounds can be achieved over Ni catalysts in a H2O–compressed CO2system at 35–50 °C without using any environmentally harmful solvent. The effective CO2pressure is much lower than the critical pressure of CO2. The hydrogenation of nitro group should be the rate-determining step. [ABSTRACT FROM AUTHOR]

Chemoselective hydrogenation of water-insoluble aromatic nitro compounds can be achieved over Ni catalysts in a H2O–compressed CO2 system at 35–50 °C without using any environmentally harmful solvent. The effective CO2 pressure is much lower than the critical pressure of CO2. The hydrogenation of nitro group should be the rate-determining step. [ABSTRACT FROM AUTHOR]

The synthesis of self-healing and recyclable polymeric materials from renewable CO2 is of great importance in the fields of functional materials and sustainable chemistry. In this work, mechanically robust poly(urea-imine) (PUI) thermosets were prepared from CO2-sourced oligourea (OUa), terephthalaldehyde (TA) and tri(2-aminoethyl)amine (TAEA) through condensation between equimolar amino and aldehyde groups. The synthesized PUIs have satisfactory mechanical performance, seal-healing and recyclable properties as they contain cross-linked dynamic imine bonds and reversible hydrogen bonds. These properties can be adjusted by changing the ratio of TAEA to OUa, thus varying the chemical bonds and chain structure. The highest values for the mechanical properties tensile stress (10.2 MPa) and Young's modulus (79 MPa) were obtained in a PUI thermoset synthesized from a molar ratio of TAEA to OUa of 3 : 2 (OUa2-T3). In addition, this thermoset can be healed at 80 °C with a healing efficiency over 92% owing to the high reversibility of imine and hydrogen bonds and the flexibility of CO2-sourced OUa chains. Moreover, it can also be reprocessed and recycled by physical and/or chemical means without change in its chemical structure, glass transition temperature and original mechanical properties. Additionally, this PUI thermoset can be easily degraded into its original reagents OUa, TA and TAEA under acid conditions. Therefore, as novel sustainable materials, the PUI thermosets reported in this article have great potential to replace conventional non-degradable thermosets over a wide field. [ABSTRACT FROM AUTHOR]