Urea‐Functionalized Swelling Poly(ionic liquid)s as Efficient Catalysts for the Transesterification and Hydrolysis of Ethylene Carbonate

Abstract

AbstractUrea‐functionalized poly(ionic liquid)s (PILs) were synthesized through polymerization of urea tethered imidazolium ionic liquid monomers (urea‐IL) with sodium acrylate, and N,N′‐methylenebisacrylamide (MBA) as a crosslinker. Close‐packed and interconnected pores (1–4 ) under swollen state could be observed from the cryogenic scanning electron microscopy (cryo‐SEM) images. The promising catalytic activity of the PILs was illustrated for the transesterification reaction of ethylene carbonate with methanol. High activity and selectivity could be achieved by using poly(urea‐IL)‐n catalysts, which was similar to that of corresponding homogeneous ionic liquid catalysts. The urea tethered imidazolium in PILs acted as hydrogen‐bonding donor to activate ethylene carbonate and intermediate 2‐hydroxyethyl methyl carbonate (HEMC) for enhancing catalytic activity. The swelling ability of urea‐functionalized PILs in methanol enabled active urea sites accessible for substrates. However, the complete conversion of ethylene carbonate was limited by reversible reaction between ethylene carbonate and HEMC. A possible synergistic activation mechanism for the transesterification reaction was proposed and supported by NMR titrations. The catalyst can be reused and recycled five times with stable activity. Furthermore, urea‐functionalized swelling PILs also exhibited high catalytic activity for the hydrolysis of ethylene carbonate.