Deep eutectic solvents (DESs) have attracted broad attention due to their low cost and toxicity, easy preparation, good biological compatibility and similar characteristics to those of ionic liquids. In this study, a DES system composed of choline chloride and urea has been applied for the controllable degradation of polyurethane (PU). By the combination of Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR) and matrix-assisted laser analytical ionization time-of-flight mass spectrometer (MALDI-TOF-MS), the selective cleavage of carbamate and urea bonds with little damage on carbonate bonds was achieved in the DES system by the regulation of reaction conditions, which favored the recovery of both valuable polycarbonate diol (PCDL) and 3,3′-Dimethyl-[1,1′-biphenyl]-4,4′-Diamine (o-toluidine). The degradation rate of PU and the yield of PCDL reached 100% and 57.4% respectively under mild conditions (1 atm, 170 °C, 8 h). A possible degradation mechanism was proposed based on the experimental results, in which the synergistic effect of choline chloride and urea activated largely the carbamate bond and thus led to a controlled degradation of PU.
Yutao Tong,Ruihua Cheng,Huan Dong,Zhen Liu,Jinxing Ye,Boping Liu
A series of bifunctional hexanuclear organoboron catalysts with dual-arm structures were facile prepared via a two-step procedure in ~100% yields featuring six boron centers and two quaternary ammonium bromides for the epoxides/CO 2 copolymerization . The boron active sites within the p- Hexa B , m- Hexa B , and o- Hexa B catalysts were like two stretched “arms” presenting the cooperative intramolecular structures as para-, meta-, and ortho-locations, respectively. For propylene oxide (PO)/CO 2 copolymerization, the catalysts exhibited > 99% polymer selectivity under 25 – 60 ℃. The p- Hexa B catalyst provided the highest carbonate linkages (88%) in the poly(propylene carbonate)s while the o- Hexa B catalyst generated much more ether linkages as 45%. The o- Hexa B catalyst performed higher activity in cyclohexane oxide (CHO)/CO 2 copolymerization, obtaining fully alternating poly(cyclohexane carbonate)s with > 99% polymer selectivity under 25 – 150 ℃. For electron-withdrawing epichlorohydrin (ECH) monomer , the catalysts showed highly selective copolymerization (>99% polymer selectivity) and enhanced activity in comparison with tetraboron catalysts, providing poly(chloropropylene carbonate)s with > 99% carbonate linkages under 25 – 40 ℃. A novel bilaterally sequential copolymerization mechanism for alternating epoxide/CO 2 insertion was proposed and verified by density functional theory (DFT) calculations. Bearing dual-arm intramolecular structures, the catalysts withstood the simultaneous growth of two polymer chains, achieving the enhanced activity for the copolymerization. Thus, up to seven effective boron pairs were found in the o- Hexa B catalysts within the unique cooperative structure, leading to the PO homopolymerization in the copolymer with high ether linkages. Meanwhile, the o- Hexa B catalyst with enough steric space exhibited higher activity than p- Hexa B and m- Hexa B catalysts during the copolymerization.
Jingjing Qin,Liyan Liang,Xiaohong Liu,Jiaming Liu,Dingsong Wang,Min Shi,Chaolong Yang
In this paper, a series of small monomers were synthesized to explore the dynamic reversible properties of phenol-carbamate bonds (PCBs), and the bimolecular exchange mechanism of PCBs was verified. Based on this mechanism, a novel thermo-healing recyclable epoxy resin with high mechanical performance and shape memory function was successfully developed. Meanwhile, the number of reversible phenol-carbamate bonds in this system was increased by molecular structure design, which increased the chance of reversible cleavage and recombination of the dynamic covalent bonds . Compared with our previous work, the thermo-healing efficiency of the epoxy thermosets was greatly increased, and the target polymer achieved an excellent balance between high thermo-healing efficiency and good mechanical performance. Further post-treatment experiments show that the cured epoxy resin can also be well recycled by solvent degradation or hot-pressing process. What's more, a novel carbon fiber (CF) reinforced polymer composite material was synthesized by taking that prepared epoxy thermoset as a matrix, which greatly improve the mechanical properties of epoxy resin, and the CF cloths can be recycled when the epoxy resin is removed by chemical degradation . In addition, due to the existence of reversible crystallizable switching segments in the epoxy resin system, when the temperature is above its T g , it can be triggered by thermal energy, so that the film can rapidly recover from the temporary shape to the permanent shape. This study also provides a new direction for the development of novel multifunctional intelligent polymers.
危险品化学品经营许可证（带存储）