Preparation Of Polystyrene Nanoparticles Supported Alkalic Ionic Liquids And Their Application In Knoevenagel Condensation As Catalysts

With the development of green chemistry,Ionic liquids（ILs）have increasingly attracted interest in recent years and widely been used in the field of catalysis mainly due to their excellent properties.However,like other homogeneous catalysts,ILs show excellent catalytic efficiency but poor recovery performance.The polymer immobilized ionic liquid catalysts combine the superior performance of ILs and the corrosion resistance to acid and alkali,excellent stability and modifiability of polymer carriers,effectively reducing the usage of ILs and improving the recovery performance of catalysts.The present work described in detail the preparation of two kinds of polystyrene nanometer-sized particles supported alkalic 1-propyl imidazole ionic liquids and their catalytic performances in Knoevenagel condensation.The results are as follows:（1）The cross-linked chloromethyl functionalized nanometer-sized polystyrene particles（Nano-CLPS-CH₂Cl）with 137 nm of average particle size were prepared by miniemulsion polymerization,then 1-propyl imidazole ionic liquids were successfully immobilized on CLPS-CH₂Cl,followed by introducing basic anions by ion exchange,and nano-CLPS-CH₂-[p IM][B]catalysts were obtained eventually.It proved that this kind of catalyst exhibited a good thermal stability（decomposing above 200°C）and their alkali amount was more than 1 mmol/g.Due to their high specific surface area and good dispersion,the prepared nano-CLPS-CH₂-[p IM][OH]catalysts showed an excellent catalytic activity over 92%for Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate in a methanol phase,as well as Na OH.Notably,the yield for nano-PS-CH₂-[p IM][OH]catalyzing this reaction in the aqueous phase reached 74%,and decreased 10%after 8-times reusing,better than Na OH and Micro-CLPS-CH₂-[p IM][OH]prepared by the suspension polymerization.In addition,among nano-CLPS-CH₂-[p IM][B]catalysts（B=OH、Im and Ac）,Nano-PS-CH₂-[p IM][Ac]showed a relatively lower but more stable catalytic efficiency.（2）Chloromethyl functionalized core-shell polymer nanospheres with 118nm of average particle size were synthesized by preparing polystyrene cores as seed with miniemulsion polymerization at first,then polychloromethyl styrene shell prepared using a balance swelling method with a redox initiator at a low temperature.Then basic propyl imidazole ionic liquids were successfully immobilized on particles,and Nano-CSPS-CH₂-[p IM][OH]catalyst was obtained eventually.Although the core-shell microspheres were agglomerated after loading ILs,the basic ion exchange ratio reached 28.5%.It exhibited a good thermal stability（decomposing above 200°C）with a basic loading of 0.464 mmol/g.The catalytic activity of this catalyst in Knoevenagel condensation reaction in methanol was up to 83%,and 69%in the aqueous phase,higher than that of Na OH in aqueous phase.However,its catalytic efficiency in both phases decreased 23%and 31%respectively after 4times recycling,due to the loss of ILs polymers physically adsorbed on the carrier.Its catalytic performance was no better than Nano-CLPS-CH₂-[p IM][B].The two polystyrene-supported ionic liquids nanometer-sized catalysts prepared in present work showed excellent catalytic performances in Knoevenagel condensation reaction in the aqueous phase,they will have a significant potential application for organic reactions in the aqueous phase.