Efficient synthesis of dimethyl carbonate via transesterification of ethylene carbonate catalyzed by swelling poly(ionic liquid)s

The synthesis of dimethyl carbonate (DMC) via transesterification of ethylene carbonate (EC) and methanol (MeOH) was an environmental and practical strategy. Herein, poly(ionic liquid)s (PILs) with swelling abilities were synthesized by free radical copolymerization of N-vinylimidazolium ionic liquids, sodium 4-vinylbenzoate and cross-linker (1,8-triethylene glycoldiyl-3,3ʹ-divinylimidazolium bromide ([(EG)₃-DVIm]Br₂). The swelling abilities of PILs in various solvents were measured, and PILs could swell in methanol (MeOH). The swelling ability of PILs in MeOH could be modulated by changing the cross-linker content and chain length of 3-alkyl-substituents on imidazolium. The swollen state of PILs in MeOH presented a porous cross-linked network structure observed by the cryo-scanning electron microscope (cryo-SEM). The swelling PILs were used to catalyze the transesterification of ethylene carbonate (EC) and MeOH to prepare the DMC, and the catalytic activities was correlated with the swelling abilities of PILs. The PIL with 3-butyl-substituent and 2.5 mol% cross-linker (poly[VBIm-VBA-DVIm]-2.5%) had the highest swelling ratio (Q = 12.4 (g/g)) in MeOH and EC mixed solvents and exhibited excellent catalytic activities, which was similar to corresponding homogeneous ionic liquid. Furthermore, the catalyst could be reused up to seven runs without any considerable loss of its initial activity.