Synthesis of zinc(II) complex-containing thermo-responsive copolymer based on activated ester functionalization and its catalysis application

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 -OEGMMA 300 ) of activated ester monomer N-methacryloxysuccinimide (MASI), ethylene glycol methyl ether methacrylate (DEGMMA) and oligo(ethylene glycol) methacrylate (OEGMMA 300 ) 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 -OEGMMA 300 ) copolymers was controlled by adjusting the mole fractions of the monomers. The synthesized copolymers were well characterized by proton nuclear magnetic resonance spectroscopy ( 1 H 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 -OEGMMA 300 ) based on activated ester functionalization, and further coordinate with ZnCl 2 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.