Formation and Depolymerization of Oligomers during Thermal Cracking of Silicon-Containing Carbamates.

Polymerization reactions in the thermal cracking of N-substituted carbamates to produce the corresponding isocyanates significantly reduce the yield of isocyanates and thus vastly hinder the industrial application of such non-phosgene routes. Herein, we tried to recycle the oligomers generated during the thermal cracking of 3-ethylcarbamatopropyltriethoxysilane (CPTS) to produce 3-isocyanatopropyltriethoxysilane (IPTS). Firstly, the polymerized substrates of the pyrolysis reaction were analyzed by NMR, IR, MALDI-TOF-MS and TG, indicating the pyrolysis substrates were mixtures of CPTS (25 wt%), polyureas (74 wt%), imines, and other compounds (<1 wt %). The polyureas were generated by reaction of CPTS and IPTS. Then, the depolymerization of these polyureas was realized via alcoholysis in the presence of urea. It was found that the urea not only provides a carbonyl group source, but also forms hydrogen bonds with polyureas. In addition, NH3 co-produced can also modify the reaction system microenvironment, which might be favorable for the dissociation of polyureas. With optimized conditions, more than 96 % of polymerized substrates could be reverted to CPTS for secondary cracking.

Preparation of Carbon Nanotubes/Manganese Dioxide Composite Catalyst with Fewer Oxygen-Containing Groups for Li-O2 Batteries Using Polymerized Ionic Liquids as Sacrifice Agent.

Considering the significant influence of oxygen-containing groups on the surface of carbon involved electrodes, a carbon nanotube (CNT)-based MnO2 composite catalyst was synthesized following a facile method while using polymerized ionic liquids (PIL) as sacrifice agent. Herein, the PIL (polymerized hydrophobic 1-vinyl-3-ethylimidazolium bis ((trifluoromethyl)sulfonyl)imide) wrapped CNTs were prepared. The composite was applied to support MnO2 by the treatment of KMnO4 solution, taking advantage of the reaction between PIL and KMnO4, which excludes or suppresses the oxidation of CNTs, and the as-synthesized material with fewer oxygen-containing groups acted as a cathode catalyst for Li-O2 batteries, directly avoiding the application of binders. The catalyst shows enhanced activity compared to that of the samples without PIL, as verified by the lower overpotential during discharging and charging (0.97 V at the current density of 100 mA g-1). Meanwhile, the performance parameters such as Coulombic efficiency and rate capability were also improved for the Li-O2 battery utilizing this catalyst. Further, the formation of confined Li2O2 particles could be responsible for the reduction of charge potential of Li-O2 batteries due to the synergy effect of the intrinsic catalytic activity of MnO2 and fewer oxygen functional groups on the catalyst surface.