Controllable Preparation, Functionalization And Application Of Polymorphic Polyphosphazene Micro-and Nanomaterials And Their Composites

In this paper, based on the characteristic of phosphazene chemistry, a new template induced self-assembly mechanism (building unit is nanoparticle and the connection between units is chemical bond) was suggested from the view of meso-scale point, different from the normal molecular scale self-assembly (building unit is molecule or macromolecule and the connection between units is nonchemical bond). On the one hand, to provide a novel method to preparing one dimensional polymer nanomaterials, widening the research area of meso-scale assembly field; on the other hand, with the help of nanotechnology, to explore the application of cyclomatrix-type poly phosphazene nanomaterials in high-tech fields. Special research content and results are as follows.In the reaction system with hexachlorocyclotriphosphazene (HCCP) and 4,4'-sulfonyldiphenlo (BPS) as comonomers, triethylamine (TEA) as acid-acceptor, and acetone as solvent, an optimum condition for preparing poly(cyclotriphosphazene -co-4,4'-sulfonyldiphonel) (PZS) nanofibers was obtained through checking the influence of different conditions such as temperature, ultrasonic power, monomer concentration, and feeding methods on the morphology of as-synthesized product. Under the optimum condition, with the help of SEM and TEM, we tracked the evolution process of PZS nanofibers and suggested a formation mechanism of nanofibers—in situ template induced self-assembly. Based on this mechanism, we obtained PZS nanofibers with diameter of 40～60 nm, length of several micrometers and initial thermal decomposition temperature of 444°C, which could be prepared in ten minutes under room temperature.Based on the proposed mechanism of in situ template induced self-assembly, polymorphic PZS nanotubes (capsicum-like, uniform and branched) and functionalized PZS nanotubes were prepared separately. All these nanotubes owned a highly cross-linked chemical structure. Results of nitrogen adsorption test showed that the surface of as-synthesized nanotubes possessed micro- and mesopores. The unique structure is expected to make them as drug carriers, adsorption materials and nanoreactors. In addition, the morphology change of as-synthesized product could be realized from nanotubes to microspheres by changing the polarity of reaction solvent or ultrasonic power.Taking the PZS micro- and nanomaterials as precursors, a new road to carbon materials including porous carbon spheres, carbon nanotubes and nanofibers was developed through high temperature carbonization. The specific surface area and pore volume of carbon materials could be controlled by adjusting the size of carbonization temperature or keeping time under high temperature. Characterization results showed that the pore diameter distribution of the carbon materials was centered at 0.5～1 nm and their formation originated from the escaped non-carbon elements.Based on the external template induced self-assembly mechanism, Ag/PZS (core/shell) coaxial nanocables were prepared, which had typical characteristics as follows: (1) the shell materials possess highly stable cross-linked structure with 440°C of initial thermal decomposition temperature, much higher than that of the normal linear polymer for shell materials, and thus cross-linked PZS as shell layer could better protect the metal nanowires as core layer; (2) the shell thickness of nanocalbes could be adjusted from 80 to 300 nm through changing the molar ratio of comonomers to silver nanowires, meeting the needs of different occasions on the coaxial nanocables; and (3) the preparation of Ag/PZS nanocables was performed without use of any surfactants or protective agents at room temperature, which process was simple, easy to control and reduce energy consumption.On the basis of the external template induced self-assembly mechanism, multi-wall carbon nanotubes (MWCNTs) were modified by polyphosphazenes successfully. As for the modification process, this method had the following advantages: (1) the PZS-functionalized carbon nanotubes could be easily dissolved in water and most organic solvents such as DMF, acetone, THF, and ethanol, (2) the non-covalent wrapping process of PZS on the carbon nanotubes was based on the external template induced self-assembly mechanism, rather than the conventional n-n interaction, (3) the wrapping process could be performed in one pot at room temperature, without using any surfactants or synergists, and thus the post-processing was simplified, and (4) the wrapping layer thickness on the MWCNTs could be controlled.Si@PZS composite nanospheres with 5～10 run shell (PZS) thickness were prepared successfully using HCCP and BPS as comonomers, and TEA as acid-acceptor at room temperature. After carbonization of the composite nanospheres at 900°C , Si@C nanocomposites with porous carbon layer were obtained. The electrochemical measurements showed that the carbonization samples exhibited a high specific capacity of 1200 mAh/g, a high first charge-discharge efficiency of 73.8%, and an excellent cycling stability. The superior electrochemical performance makes the Si@C nanocomposite as a promising cathode material for lithium-ion batteries.