Preparation Of Polyethylene Glycol Grafted On PEG-GMA/MMA Microspheres And Studies On Its Phase Transfer Catalysis

Phase transfer catalysis (PTC) is now established as a versatile and important synthetic technique in organic chemistry, it has been widely used in industrial and organic chemistry. However, for Liquid–liquid phase-transfer catalysis (LL-PTC) system in which soluble phase transfer catalysts are used, two major problems are always encountered, the separation and purification of the final product, and the recovery and reuse of the catalyst . For the triphase catalysts, phase transfer catalysts are chemically bound to solid supports, it has been one of the most important domain of catalysis chemistry and organic chemistry at present. In this paper, a novel grafted triphase catalyst was gained based on the polymeric support PGMA/ MMA. The triphase catalyst was used in the esterification reaction of n-chlorobutane in organic phase and benzoic acid in water phase, and some valuable research results were found.Firstly,Ternary copolymerization was performed with suspension polymerization method by using Glycidyl methacrylate (GMA) as main monomer, methyl methacrylate (MMA) as comonomer, ethyl glycol dimethacylate (EGDMA) as crosslinker and polyvinyl alcohol as disperser, and crosslinked terpolymer microspheres GMA/MMA/EGDMA were obtained. The chemical structure of the microspheres was characterized with infrared spectrum (FTIR) and their morphology was observed with scanning electron microscope (SEM). The experimental results show that among those factors, the used amount of the disperser, the stirring rate and the ratio of oil phase to water phase are three key factors. As the used amount of the disperser is less than 1wt%, the stirring rate is lower than 250rpm and the ratio of oil phase to water phase is greater than 1:4 (V:V), balling process can not be realized in the copolymerization system. The addition of electrolyte NaCl conduces to the balling process, and the grain size of the microsphere decreases with increasing the added amount of NaCl. Via controlling the various reaction conditions of the suspension copolymerization, the crosslinked copolymer microspheres GMA/MMA/EGDMA with excellent sphericity and controllable particle diameter in a range of 100-400μm can be gained.There are lots of epoxy groups on the surfaces of GMA/MMA microspheres. Via ring-opening reaction, polyethylene glycol (PEG) was grafted onto the surfaces of microspheres GMA/MMA in the coupling graft manner, the immobilization of PEG was realized, and a kind of phase-transfer catalysts PEG-GMA/MMA, namely, triphase catalyst, was prepared. In this work, the effects of various factors on the grafting reaction of PEG were mainly studied, and the reaction mechanism was investigated. The experimental results show that the Lewis catalysts are more effective than protonic acids for the ring-opening reaction of epoxy groups. The polarity of the solvents affects the coupling graft reaction between PEG and microspheres GMA/MMA greatly, and to use the solvents with higher polarity is advantageous to the graft reaction. Under the suitable conditions, the PEG graft degree of the grafted microspheres PEG-GMA/MMA can get up to 0.20g/g.The solid catalyst catalyst PEG-GMA/MMA was used in the esterification reaction of n-chlorobutane in organic phase and benzoic acid in water phase. The experimental results show that the esterification reaction occurring actually in organic phase follows a pseudo-first-order rate law,the polarity of the organic solvent, the ratio of oil phase to water phase and the density of the grafted PEG on PEG-GMA/MMA microspheres affect the reaction rate greatly.Some rules were specially found in the study:to use the solvent with high polarity is appropriate, the a adequate volume ratio of oil phase to water phase is 2:1, and the optimal grafted density of PEG on the polymeric microspheres is 15g/100g. The catalyst exhibits fine catalysis activity and selectivity, the conversion of n-chlorobutane can reaches 55% at 55℃in 6h as only 1g of PEG-GMA/MMA microspheres is added. Triphase catalysts offer many advantages associated with heterogeneous catalysts such as easy separation from the reaction mixture and reusability. The activity of PEG-GMA/MMA microspheres is not nearly decreased after reusing for ten recycles.