Research On The Preparation Of Structural Heteropolyacid Composite Microspheres Based On The Polymerizable Surfacant

A microchemical reactor, or microreactor, is one of several chemicalengineering unit process devices that are now being designed on the micrometer (asopposed to the meter) scale. The potential advantages of using a microreactor, ratherthan a conventional reactor, include better control of reaction conditions, improvedsafety, and portability. Better control of reaction conditions refers to the ability toprecisely control the temperature of the reactor, a direct result of the reactor'sextremely high surface to volume ratio. Improved safety results from the reactor'sextremely small size. Based on these advantages, microreactor technology has becomea very attractive area. Although there are many types of micro-reactors on themanufacturing technology, it can be divided into micelle technology andmicro-manufacturing technology. Generally, microreactor based on micelle technologycan be divided into reverse micellar microreactor, polymer microreactor, templatemicroreactor, etc. This research mainly focuses on the preparation of potentialmicroreactors based on structural heteropolyacid composite microspheres.The main advantage of the structural heteropolyacid composite microspheres is themicrosphere with water-soluble core and phase transfer catalysts shell. So, thismicrosphere material can be used as microreactor for two-phase transfer catalysis. Themicrosphere can store water-soluble substance in the core and perform potentialcatalysis at the interface. Addtionally, the advantage of the composite microspheresincludes two aspects. One is that the micrometer size of the composite microspheremakes its easy separation from the system. Another is that the surface of the compositemicrosphere has structural morphology in micro-nano scal to result in goodperformance in catalysis. In order to meet these requirements, a polymerizablesurfactant methacryloxyethyl dodcydimethyl ammonium bromide (DMDB) wasintroduced in the microgel of poly acrylamide (PAM) by copolymerization andInterpenetrating polymer networks (IPN) methods, respectively. After that, thestructural heteropolyacid composite microspheres were prepared by ionic exchange.This research includes the following parts.(1) The new type polymerizable surfactant DMDB was synthesised. DMDB was synthesised by reaction between dimethylamminoethylmethacrylate (DM) andn-dodecanebromide. The product was characterized by infrared spectrum (IR),¹H-NMR and elemental analysis. The optimal reaction conditions are: theconcentration of reactants in acetone is 15-17%; the reaction time is 10 h; the reactiontemperature is about 50℃and the ratio of DM to C₁₂H₂₅Br is 1.15:1. Under theseconditions, the best yield of 42.05% was obtained.(2) P(AM-co-DMDB) microspheres were prepared by reverse suspensionpolymerization technique. In this experimental section, the effects of monomer's ratios,amount of emulsifiers, stirring speed, continuous phase and reaction time on themonodisperse and size of microspheres were studied. The composite microspheres,P(AM-co-DMDB)/PWO were prepared through ion-exchange betweenP(AM-co-DMDB) microspheres and heteropolyacid. The composite microspheresmaterial, P(AM-co-DMDB)/PWO, has been characterized by the SEM,FTIR,TGA,XRD and EDX etc, respectively.The results demonstrated that the composite material in shape was generallymicrospheres with the different surface morphology. The composite microspheres withmicrometer size in entire and nanometer morphology in surface were observed. Withaddition of DMDB in the template microspheres, the surface morphology of compositemicrospheres regularily changed. The more contents of DMDB, the more obvioussurface-wrinkly morphology is. These observations are attributed to the increase ofheteropolyacid in the composite microspheres, and which can be interpreted by amechanism of "framework confining deposition and deposition inducing distortion". Itis not difficult to understand that the preparation of composite microspheres withcontrollable surface morphology and heteropolyacid amount is significant inenhancement of potential catalytic properties. So, this reaction is very useful inapplication of this composite material.(3) In this section, interpenetrating polymer networks (IPN) method was employedto prepared the IPN(AM-PDMDB)/PWO composite material. PAM microspheres werefirstly prepared by reverse suspension polymerization technique, and then the PAMmicrospheres swelled by water containing ammonium persulfate (APS) were freezedlydried. The freeze-dried PAM microspheres were immersed by the polymerizablesurfactant DMDB, and polymerization was finally initiated. By this method, the IPNmicrospheres composed of PAM and PDMDB were obtained. The IPN(AM-PDMDB)/PWO composite microspheres with potential catalysis were finallyprepared by ionic exchange between IPN microspheres and heteropolyacid. Themorphology and loading amount of heteropolyacid of the composite microspheres havebeen characterized by SEM,FTIR,TGA,XRD and EDX, respectively.The results demonstrated that the composite materials in shape were generallymicrospheres with different surface morphology. The composite microspheres withmicrometer size in entire and nanometer morphology in surface were observed. Theamount of DMDB significantly affected the surface morphology ofIPN(AM-PDMDB). With the increase in dosage of DMDB, the porous structure on theIPN(AM-PDMDB microspheres become significant. Base on the IPN(AM-PDMDBmicrosphere as template to prepare the composite microspheresIPN(AM-PDMDB)/PWO, the surface wrinkle of the composite microspheres becomedense and fine with the increase BA and heteropolyacid H₃PW₁₂O₄₀ concentration.Such structural features can be expained by the mechanism of "framework confiningdeposition and deposition inducing distortion" mentioned above. Comparied withcopolymerization to prepare the composite microspheres, the IPN polymeric method isan efficient one to increase DMDB in the template microspheres, and more PDMDBlocates in the surface of the composite microspheres. These features are very useful forenhancement of this composite material in application of catalysis.