Controllable Construction Of Porous/Hollow Polymer Microspheres For The Enpsulation Of Salts Dissolved In Solutions

Due to the characteristics of large specific surface area,low density,high encapsulation capacity,and additional internal space,porous/hollow microspheres have shown potential applications in the fields of energy,catalysis,sensors,and controlled drug release.When the porous/hollow microspheres are used as the carriers for the loading of guests(small molecules,macromolecules,or even nanoparticles),the as-formed complex structures show many excellent properties,and realize the synergistic effects between the shell and the encapsulated guest.Due to the wide designability of the composition,structure,phase state and function,polymers show unique advantages in the construction of functional porous/hollow polymer microspheres.Templating method,selective etching,self-assembly and other methods have been widely used in the preparation of porous/hollow polymer microspheres,but the development of simple,efficient,and extendable pore-/cavity-creation methods remains attractive in polymer microspheres.In this work,starting from the multifunctional amino-containing monomer,aldehyde-containing monomer and H3PO3,we synthesized a type of polymer microspheres(denoted as NOPs-o)crosslinked by both imine and carbon-nitrogen single bonds through Kabachnik-fields reaction.Based on the dynamic characteristics of imine bonds,porous/hollow polymer microspheres(denoted as NOPs)were prepared by selective etching of NOPs-o through the imine bond exchange reaction.We found that NOPs could efficnently encapsulate metal salts in solutions,thus developing a controllable and high adaptability preparation method for metal salts@NOPs.The main research work is as follows:(1)Using 1,3,5-tris(4-aminophenyl)benzene,p-benzodialdehyde and H3PO3 as monomers,NOPs-o cross-linked by dynamic imine bonds and nondynamic carbon-nitrogen single bonds was prepared by Kabachnik-fields reaction.NOPs were then fabricated by selectively etching NOPs-o through the exchange reaction of dynamic imine bond caused by guest primary amino molecules.The influence of etching time on the morphology and structure of NOPs was studied,and the composition,morphology and pore/cavity structure evolutions of the microspheres during etching were tracked.The main reason for this etching process is that when a guest primary amine molecule replaces the 1,3,5-tris(4-aminophenyl)benzene component in the polymer network,it is accompanied by the Kirkendall effect.(2)Using NOPs as carriers,a simple and efficient method for encapsulating soluble metal salts was developed.The introduction of NOPs into the metal salt solution can realize the enrichment and crystallization of the salts in interior of the cavity,forming metal salts@NOPs core-shell structures.We used more than ten kinds of metal salts like LiCl,NaCl,KCl,CH3COOK,Na2SO4,Cu(NO3)2,and FeCl3 to study the universality of this encapsulation method.By analyzing the changes in solution conductivity,fluorescence and other properties during the encapsulation process,as well as characterizing the morphology and crystal structure of the core-shell structures,the mechanism for the encapsulation of metal salts in NOPs was preliminarily discussed.We consider that the concentrating effect and crystallization of the soluble metal salts in the cavity in a confinement space may be the main deriving force for the encapsulation of metal salts in NOPs.