Stimulus Responsive Polymeric Interfacial Catalyst:Preparation And Its Application In Heterogeneous Reaction

In recent years,organic small molecule catalysts and enzymes have attracted considerable amount of attention due to their high catalytic activity and selectivity.However,it is difficult to the recycling and separation of these homogeneous catalysts from the heterogeneous system,which significantly limits the large-scale application of TEMPO and lipase.Although immobilizing them on an insoluble support can be used to enhance the recovery of catalyst,heterogeneous catalysts suffer from low catalytic activity.The stimuli-responsive interfacial catalysis is an extensively utilized,well-demonstrated strategy to address these two coexisting problems.The polymeric interfacial catalyst acts as a Pickering emulsifier to stabilize the two immiscible solvents to form a stable Pickering emulsion,which greatly increases the reaction interface area and reduces the mass transfer distance between the two phases.Moreover,it also catalyzes the reaction at the interface of two immiscible solvents.In addition,the surface of the solid particles can be switched to hydrophobicity under the influence of external stimuli,resulting in de-emulsification of the Pickering emulsion to achieve rapid separation of the catalyst and product.Based on this,three different stimuli-responsive polymeric interfacial catalysts were synthesized via surface design and adjustment on the basis of polymer,and constructed a highly active,easily separated,low energy consumption catalytic system.Their catalytic activity,the substrate scope of the reaction and stability were investigated.Corresponding contents are divided into three parts:?1?The synthesis of a pH-responsive polymeric interfacial catalyst(SCBI-PAEK-6F-C₁₀-TEMPO)via one-step grafting of TEMPO onto a polyaryletherketone having pendant benzimidazole groups?SCBI-PAEK-6F?,and the pH-responsive of the Pickering-Montanari catalytic oxidation system was prepared.This well-designed polymer has been applied in the oxidation of alcohols under the Montanari conditions.It is found that functionalized polymer can aggregate at the water-oil interface and act as an effective stabilizer to facilitate the formation of a stable Pickering emulsion,which shows outstanding catalytic activity for alcohol oxidation through the microreactor mechanism.Compared with free TEMPO,the activity of SCBI-PAEK-6F-C₁₀-TEMPO was increased by 1.6 times.Moreover,the catalyst can be efficiently catalyzed to oxidation of various alcohol substrates to the corresponding aldehyde or ketone.After the end of the reaction,the PIC is featured with desirable high pH responsiveness due to the valuable benzimidazole groups.De-emulsification of the Pickering emulsion reaction system can be conveniently triggered by simply tuning the system pH value to 3,thus facilitating the facile recovery of the PIC.In addition,the sustainable catalyst can be reused for subsequent cycles of alcohol oxidation without appreciable loss in catalytic activity or selectivity.?2?A novel CO₂-responsive TEMPO immobilized nanoparticle polymeric catalyst?P?TMA-co-DEA??was synthesized through"one-pot method"distillation-precipitation polymerization of the precursor monomer2,2,6,6-Tetramethyl-4-piperidyl methacrylate?TMPM?,the crosslinking agent divinylbenzene?DVB?.The TEMPO loading as well as surface hydrophilicity could be finely tuned via simply adjusting the diethylaminoethyl methacrylate?DEA?monomer fraction during polymerization.The TEMPO loading is from 2.4 mmol·g^-1to 1.0 mmol·g^-1,and the contact angle is changed from 114°to 90°.At the same time,the effects of oil phase solvent,oil-water volume ratio,particle concentration and pH on the stability of P?TMA-co-DEA?-4 stabilized Pickering emulsion were systematically investigated.In addition,a Pickering-Montanari catalytic oxidation system with CO₂-responsive was constructed.It was found that complete conversion of benzyl alcohol can be achieved within 15 s using P?TMA-co-DEA?-4.Compared with free TEMPO,its catalytic efficiency was improved by 2.3 times,showing excellent catalytic activity.After the reaction is completed,the emulsion can be de-emulsification by CO₂,and the catalyst is recovered by centrifugation.After 10cycles,it was found that the catalyst catalyzes the conversion of benzyl alcohol to benzaldehyde without significant loss of conversion and selectivity,which exhibits excellent stability.?3?Surface aminated magnetic nano-polystyrene microspheres?Fe₃O₄@PS-NH₂?were prepared by miniemulsion polymerization.Bi-phase system is introduced for synthesizing amphiphilic magnetic nano-polystyrene microsphere-loaded lipase catalyst?Fe₃O₄@PS-NH₂/lipase?.Its unique amphipathy properties provide a good emulsification function for the two-phase system of soybean oil and methanol.Pickering emulsion with high stability provides a good platform for static transesterification.The yield of biodiesel using Fe₃O₄@PS-NH₂/lipase-3 catalyst catalyzed transesterification reaction reached 89.3%at 30 h.In addition,the catalyst can achieve rapid separation and recovery by magnetic-responsive.In the following five cycles of transesterification,the yield of biodiesel showed little loss.