Modification And Application Of Cagelike Polymeric Microspheres

Cagelike microspheres, as a kind of macroporous materials, possess plenty of advantages including large pore size and pore volume, which results in various applications such as catalysis, chromatography, controlled release, sensor, absorption, and separation. Compared to microporous and mesoporous microspheres, they are capable of loading macromolecules and nanoparticles, and have higher loading capacity. Due to the large pore size, the diffusion of the substance inside the cagelike microspheres is so fast, leading to some problems in practical use. For example, it is difficult to achieve the controlled release of the loaded species from the macroporous carriers. Thus the modification and functionalization on cagelike microspheres are necessary for the application demands.The introduction of hierarchical meso-macroporous structure is a feasible strategy for the modification of macroporous microspheres because it can combine the advantages of macroporous and mesoporous materials, i.e., the high loading capacity and mass diffusion rate in macroporous, as well as the controlled release in mesopores. Grafting functional groups or polymer chains on macroporous microspheres is another strategy, especially to prepare intelligent carriers to achieve stimuli-responsive release. Moreover, if macroporous microspheres are composited with some barrier materials, such as 2D-planar structuredgraphene oxide (GO), the pores can also be covered by GO sheets so as to achieve the controlled release.Based on our previous works on the preparation of cagelike polymeric microspheres, This work deeply studied the modification of polymeric cagelike microspheres using the above three strategies:fabricating hierarchical meso-macroporous structured microspheres, radiation-induced RAFT grafting modification on the surface of cagelike microspheres, and preparing cagelike porous polymer/GO composite microspheres. At the same time, the corresponding application for each modified cagelike microspheres had also been investigated. The major contents and results are demonstrated as follows:1. Cagelike microspheres were prepared via swelling-osmosis process and the effects of solubility parameter of polymer and hydrophilicity of microspheres on the morphology were investigated. Based on the above results, hierarchical meso-macroporous cagelike microspheres were fabricated by two-step swelling-osmosis process. Cagelike macroporous microspheres were synthesized from SPS microspheres at first, and then MMA was added. MMA could swell into the cagelike macroporous SPS microspheres and the polymerization of MMA was initiated, which induced the phase separation of PMMA and SPS. Cagelike meso-macroporous microspheres were obtained after removal of PMMA domains as porogen for meso pores by extraction with acetic acid. The thorough investigation of factors influencing the size of the mesopore, including the preparation method of PS microspheres, the dose rate and absorbed dose when PS microspheres was synthesized via radiation dispersion polymerization, the component of the swelling system, the amount of MMA and its polymerization time, was studied. It laid the theoretical foundation of synthesizing cagelike microspheres with different structures.2. Cagelike SPS/PMMA microspheres containing trithiocarbonate DMP were synthesized through Pickering emulsion. The influence of the molecular weight of PS, the addition of DMP, the preparation method and hydrophilicity of PS microspheres on the morphology of cagelike microspheres was studied. According to the above results, cagelike microspheres with suitable pore size were selected in the further modification of radiation induced RAFT grafting polymerization of PAA. The obtained cagelike microspheres were pH-responsive and had wide application prospects in controlled release.3. Using trithiocarbonate TRITT instead of Fe2+could prevent NIPAM from gelation and achieve the radiation induced RAFT grafting of PNIPAM on cagelike SPS/PMMA microspheres. Moreover, TRITT could be immobilized on GO (GO-TR) sheets through a two-step amidation reaction. PNIPAM could be grafted on the GO-TR sheets via radiation RAFT polymerization. Terminal carboxyl groups of TRITT were converted to amino groups by amidation reaction so that the PNIPAM grafted rGO sheets were able to composite with the negatively charged cagelike microspheres in acidic condition. Because GO and rGO can convert the energy of near infrared (NIR) photons to heat, the resultant pH-responsive and thermal-responsive cagelike composite microspheres were capable carriers of anti-cancer drugs, which combined photothermal therapy and chemotherapy.4. Gold nanoparticles (AuNPs) were prepared and loaded in cagelike SPS microspheres through γ-ray radiation reduction method. The porous structure could prevent the AuNPs from aggregating, leading to a good catalytic performance and recyclability in the reduction of o-nitroaniline by sodium borohydride. Furthermore, if aminated GO (GO-NH2) was added during the preparation of composite catalyst, it would be reduced simultaneously with the precursor of gold by γ-ray radiation. AuNPs loaded rGO-NH2 sheets were obtained as a result. The resultant rGO-NH2 sheets improved the catalytic activity of the loaded AuNPs significantly, and they could composite with the cagelike microspheres in acidic condition. The cagelike SPS/rGO-NH2/AuNPs composite microspheres possessed excellent catalytic performance as well as good recyclability.