Functional Hybrid Microcapsules By The One-step Interfacial Thiol-ene Photopolymerization

During the recent years, the organic-inorganic hybrid materials haveobtained increasing attention for the researchers due to that the materialscombine the properties of organic polymer, such as flexibility, facile-process and multifunctional groups, with the advantages of inorganicmaterials in terms of mechanical strength, thermal stability, and modulus.By tuning the structure, dimension and composition of the components, thehybrid materials might exhibit excellent properties, such as mechanical,rheological, electrical, chemical, catalytic, magnetic, and optical, whichhave potential application in diagnostics, catalysis, drug delivery system,and coatings. As a typical organic-inorganic hybrid materials, functionalhybrid microcapsules have both practical and academic importancebecause of the protection of the active species and encapsulation for thecontrolled of drugs and dyes. There are a variety of approaches for thefabrication of hybrid microcapsules with tunable size and wall thickness,mainly including the self-assembly of amphiphilic block copolymer, thelayer-by-layer assembly and emulsion polymerization. The self-assemblyof amphiphilic block copolymer and the layer-by-layer assembly which can prepare microcapsules with specifically designed properties and well-defined composition extended the application fields and enriched thepreparation methods for microcapsules. But there are some limitations forsuch methods, such as tedious fabrication process and environmentallyunfriendly. In this dissertation, we choose emulsion polymerization whosemedium is water as our fabrication method, which is simple,environmentally friendly and has a good biocompatibility. The thiol-enephotopolymerization is an efficient synthesis method with the novelcharacter, such as high yields, stereospecificity, insensitivity to oxygen orwater, mild reaction conditions.In this dissertation, one-step interfacial thiol-ene photopolymerizationis utilized to fabrication the microcapsules. We design a surfactant PTPSwhich contains thiol groups, PEG chains, alkyl chains and POSS. ThePTPS can endow the hybrid materials good mechanical performance andthermal responsive. Under the exposure of365nm UV light, PTPScrosslinked with TMPTA to form the wall of microcapsules. To explore therelationship of microcapsules and the concentration of the components, wemade a series of microcapsules by tuning the feed ratio of PTPS, TMPTAand toluene and characterized them with TEM, SEM and AFM. The wallthickness of microcapsules increased while the size decreased with theincreasing content of TMPTA. With the increasing amount of toluene, thewall thickness decreased and the size of the microcapsules increased. We also researched the thermal responsive behavior of microcapsules. Themicrocapsules can dispersed in water stably at the room temperature. Whenheated to high temperature, the hydrogen bond of PEG chains and waterwas destroyed and the microcapsules aggregated and precipitated at last.This responsive behavior is a reversible process. When the precipitatedmicrocapsules is shook slightly at room temperature, they can dispersedinto water again. The microcapsules are also applied to control thedispersion of dyes successfully.To further combine the convenience of photoreduction and the stabilityof microcapsules, we developed another functional microcapsulescontaining metal nanoparticles (gold nanoparticles, silver nanoparticlesand platinum nanoparticles). We use a similar way to fabricate themicrocapsules and the metal precursor was in situ reduced to formnanoparticles embedded in microcapsules. From the results of SEM andTEM, the nanoparticles with uniformed-size were almost embedded in themicrocapsules, without free metal nanoparticles in the background of TEMimages. The microcapsules containing metal nanoparticles were used tocatalyze the reduction of4-nitrophenol and4-nitro-3(trifluoromethyl)phenol. These characteristics make the hybrid microcapsules having thepotential applications such as catalysis and controlled dispersion of dyesand drugs.