Multiform Polyphosphazenes Nano/Micro Materials, Preparation And Further Applications

Rare-earth doped up conversion nanocrystals (UCNPs) possess advantages in the field of biomedicine for their unique photoluminescence mechanism, for example, it is possible for UCNPs to generates high-energy visible photons from low-energy radiation in NIR region. Nevertheless, UCNPs are not water soluble due to the presence of hydrophobic organic ligands (oleic acid) on the surface, and no appropriate functional groups for further biological functionalization. It is not suitable for UCNPs being used directly as imaging agents in vivo. Nanosheets are promising candidates for a vast range of applications involving catalysis support, structural and electronic components, batteries and capacitors for their special morphology and surface performance. Meanwhile, in consideration of the wide potential applications of two-dimensional nanoshseets, understanding their crumpling mechanism is important, nevertheless, the work in this area was mainly based on model in the past.In this paper, a serious of multiform polyphosphazene micro/nano materials (microspheres, nanosheets or core/shell nanostructures) were synthesized via the self-assemble of hexachlorocyclotriphosphazene with some other monomers such as p-phenylenediamine and melamine. On the one hand, polycondensation between hexachlorocyclotriphosphazene and p-phenylenediamine was conducted on the surface of rear earth doped up-conversion nano particles to form core/shell nanostructures with abundant of amino groups tagged on their surface, which not only bring the nano particles hydrophilic property, but also good surface modification property. On the other hand, a kind of organic-inorganic hybrid nanosheets, poly (cyclotriphosphazene-co-melamine), with typical thickness no more than 1 nm, were synthesized via the self assemble of hexachlorocyclotriphosphazene and melamine. The transition of the crumpled nanosheets to extended ones was studied and the transition mechanism was also analyzed, which not only extended the scope of polyphosphazenes, but also helped for the understanding of the conformation transition of nanosheets in many environments. Special research content and results are as follows.Polyphosphazene microspheres with diameters ranged from 1μm to 2μm were synthesis via the self-assemble of hexachlorocyclotriphosphazene and p- phenylenediamine with the aid of ultrasonic conditions under the protection of N2. By control the molar ratio of hexachlorocyclotriphosphazene and p-phenylenediamine, which was 1:4, microspheres with abundant amino groups tagged on their surface were obtained. Amino detection results showed that, the amino groups can reach as high as 60.0μmol/g. The influences of temperature and monomer concentration to microspheres were studied. The results indicated that, as the temperature grows, the reaction yield increased, but the size distribution of the particles increased. What's more, with the increase of the monomer concentration, paticle-to-paticle bond occurred.Further more, hybrid polyphosphazene was allowed to grow on the surface of rear earth doped up-conversion nanocrystals by in situ polycondensation between hexachlorocyclotriphosphazene and p-phenylenediamine to form core/shell nanostructures. The results suggested that, compared with up-conversion nanocrystals, the core/shell nanoparticles not only maintained good up-conversion properties, but also gained good water dispersability and surface modification property, for the abundant of amino groups on their surface, which were benefit to their biological applications.Organic-inorganic hybrid polyphosphazene nanosheets were obtained via a one-pot chemical approach. The hybrid polyphosphazene obtained directly after chemical process was not nanosheets, but microspheres, which consisted of folded and crumpled nanosheets. When the polyphosphazene microspheres were dipped in aqueous solution, it was able for the nanosheets to extend to form outstretched ones gradually. Transmission electron microscope was used to study the transition process, and the process was well characterized. The typical thickness of the nanosheets was studied by scanning probe microscope, and the results showed the thickness was no more than 1 nm. The dynamic hydration layers formed via the polymer-water and water-water hydrogen bonds may be a major factor in the transition process. Because of the formation of dynamic hydration layers on both sides of the nanosheets, nanosheets on the surface of polyphosphazene microspheres were more inclined to extend to form outstretched ones. Meanwhile, larger excluded volume of the hydrated nanosheets was formed, leading to larger repulsion among nanosheets, which would also accelerate the transition process.