Functionalized dicyandiamide-formaldehyde polymers as efficient heterogeneous catalysts for conversion of CO2 into organic carbonates

The application of the dicyandiamide-formaldehyde polymer (DFP), which is a kind of organic polymer flocculant, as a supporter for conversion of CO2 into organic carbonates was studied in this work, and four kinds of dicyandiamide-formaldehyde polymers were synthesized and employed as efficient single component, metal-free, multifunctional, polyquaternium catalysts for cycloaddition of CO2 with epoxides. The results indicated that the ammonium bromide modified dicyandiamide-formaldehyde polymer (ABMDFP) was the optimal catalyst among the four polymers and was observed to be suitable for various substrates. A possible mechanism of ring-opening of epoxides assisted by the hydroxyl and activation of CO2 induced by amines was proposed. In addition, the catalyst could be easily recovered and reused six times with only a slight loss of catalytic activity. Furthermore, the catalyst exhibited good activity in the synthesis of dimethyl carbonate (DMC) through a transesterification reaction. The functional organic polymers in this study were proved to be efficient heterogeneous catalysts for the cycloaddition reaction of CO2, which was applicable to the development of fixed-bed continuous flow reactors.