LAUSR

Abstract In this study, we report the synthesis of pybox zinc(II) complex-containing thermo-responsive copolymer through activated ester strategy and their application in Knoevenagel condensation as an efficient and recoverable catalyst. First, a series of thermo-responsive copolymers P(MASI-co-DEGMMA-co-OEGMMA300) of activated ester monomer N-methacryloxysuccinimide (MASI), ethylene glycol methyl ether methacrylate (DEGMMA) and oligo(ethylene glycol) methacrylate (OEGMMA300) were synthesized through free-radical copolymerization using azodiisobutyronitrile (AIBN) as an initiator in solution polymerization. The lower critical solution temperature (LCST) of the P(MASI-co-DEGMMA-co-OEGMMA300) copolymers was controlled by adjusting the mole fractions of the monomers. The synthesized copolymers were well characterized by proton nuclear magnetic resonance spectroscopy (1H NMR), infrared spectrum (FTIR) and gel permeation chromatography (GPC). Then, pybox ligand with a terminal amino group was introduced into P(MASI-co-DEGMMA-co-OEGMMA300) based on activated ester functionalization, and further coordinate with ZnCl2 to afford a pybox zinc(II) complex-containing thermo-responsive copolymer. The zinc complex-containing polymer displayed excellent catalytic activities for Knoevenagel condensation reaction in water at room temperature, and it can be easily recovered by centrifugation at a higher temperature, above the LCST of the copolymer after reaction. The recovered catalyst can be reused at least five cycles without obvious decrease in catalytic activity.