Synthesis and physicochemical characterization of polyoxymethylene dimethyl ethers

Polyoxymethylene dimethyl ethers (H3CO(CH2O)nCH3, PODEn or DMMn,n ≥ 2) with unique physical and chemical properties are a potential additive for diesel fuels, which can effectively enhance the combustion efficiency and reduce the emission of pollutants. In this work, a series of pure PODEn components (n = 2-5) were synthesized from methylal and trioxymethylene and obtained with high purity through collaborative separation; their structure and properties were characterized by NMR, FT-IR, Raman, DSC and DFT calculation and a detailed assignment of the expressions in the spectrogram to the various groups was performed. A detailed assignment of expressions in the spectrogram to the various groups was also performed. The density and viscosity of PODEn were measured at 298.15-323.15 K. The results indicate that the density and viscosity of PODEn decrease gradually with the increase of temperature. Meanwhile, with the increase in the number of -CH2O- units (n) from 2 to 5, the density, viscosity, flash point, pour point, and the heat of fusion and solidification of PODEn are all increased with the increase in the chain length. These results are valuable for the practical synthesis and application of PODEn.