Synthesis Of Nonionichairy-like Microspheres And Its Application For The Adsorption Of SiO₂ Nanoparticles

The monodispersed polymer microspheres with controlled surface functionality (chemical composition and micro/nano structure) have been paid much attention to in the applications of catalysis, biotechnology, information, energy, special materials and many other fields due to its unique and controlled surface properties. The surface functionality of polymer microspheres is the crucial factor to determine the preparation of composite microspheres with micro/nano hierarchical structures (such as raspberry-like polymer/silica composite spheres). Grafting polymer brush to the surface of microspheres is one of the most efficient methods to achieve surface functionalized microspheres. Polymer brushes possess many novel properties, such as surface wettability, selective adsorption, adhesion, response to the external environment, lubricity and anti-biofouling due to its distinctive structure. In this paper, we synthesized surface functionality hairy-like polymer microspheres by emulsifier-free polymerization and surface-initiated atom transfer radical polymerization (SI-ATRP), respectively, and used as templates. Then, the role of hairy-like chains of templates on the adsorption of silica particles during the in-situ sol-gel reaction and the formation mechanism of these composite particles were studied in detail. The present strategy offers theoretical guidance for adjusting the morphologies and structures of organic/inorganic composite microspheres. The main contents of the research are as follows:1. Carboxylic-functionalized, PEG-functionalized and Carboxylic-PEG hybrid functionalized polymer microspheres were synthesized by emulsifier-free polymerization and used as templates. Then, Raspberry-like or core-shell structured composite particles were successfully prepared based on the in-situ sol-gel process and the formation mechanism of these composite particles was studied in detail. The results prove that the carboxyl groups on the surface of copolymers can induce silica nucleation on the template spheres through the weak acid-base interaction; The PEG hairy chains on the surface of PEG-functionalized polymer microspheres can inhibit the aggregation of silica nanoparticles through steric repulsion; However, for Carboxylic-PEG hybrid functionalized polymer microspheres, the silica particles can nucleate on the template spheres and at the same time the PEG hairy-like chains determine the growth of silica particles during the in-situ sol-gel reaction, which make it suitable for the controllable fabrication of micro/nano structures.2. Silica template particles with PEG hairy-like chains on the surface were fabricated by ATRP for the quantitative study of how the hairy-like chains regulating the adsorption of silica nanoparticles. Firstly, monodispersed silica microspheres were prepared by Stober method, and then were modified with 3-aminopropyl triethoxysilane (APTES) introducing amino group onto the surface of silica particles. Subsequently, ATRP initiator a-bromoisobutyrylbromide (BiBB) can be also successfully introduced onto the silica particles surface via the reaction between amino groups and acylbromide groups. Finally, nonionic hairy-like microspheres were obtained by PEG-based macromonomer poly(ethylene glycol) methacrylate(PEGMA) through SI-ATRP polymerization. The rate of the polymerization can be controlled by adjusting the polarity of the solvent, and the molecular weight of poly (PEGMA) can be regulated by the reaction time and the amount of spherical initiator.3. A series of hariy-llike microspheres with different molecular weight of poly(PEGMA) brush were achieved by regulating the concentration of macromonomer via SI-ATRP and used as templates. In water/ethanol solution, diethanolamine (DEA) was used to catalyze the hydrolysis reaction of tetraethoxysilane (TEOS) and then composite microspheres with different morphologies were obtained. The results indicated that for high molecular weight polymer brushes, the silica particles can be adsorbed onto the surface of hariy-llike microspheres to form raspberry-like particles via hydrogen bonding between silica and PEG chains. However, for the low molecular weight polymer brushes, the hydrogen bonding between silica and PEG chains is relatively weak. Furthermore, hydroxyl groups in poly (PEGMA) brushes cannot induce silica in-situ nucleation on the template spheres resulting in little silica particles adsorbed onto the surface of hariy-like microspheres.