Grafting Polymers From The Surface Of Silica Nanoparticles Via Living Radical Polymerization And Their Applications

Exploitation of the fascinating properties of inorganic nanoparticles, such as optical, magnetic and electronic properties requires these particles to be dispersed homogeneously. The best way to avoid aggregation is to graft polymer chains onto the particles covalently, forming organic/inorganic hybrid materials with inorganic core and organic polymer shell have intrigued interest for the combination of the properties of both the inorganic particles and the polymer such as solubility and easy processing.Controlled radical polymerizations (CRPs) provide a powerful tool for grafting polymers from inorganic surface, because CRPs can control molecular weight and molecular weight distribution of grafted-chains in comparison with the conventional radical polymerization; they are simple on operation procedure and versatile on monomers in comparison with the ionic polymerizations.Silica nanoparticles can be synthesized by simple methods and have been widely used in many fields such as ceramics, plastics, rubber, coating, catalyst and biomedicine etc. Furthermore, many inorganic nanoparticles, including magnetic, semiconductor and metal particles can be coated with silica formed by hydrolysis of TEOS. So, in this paper, CRPs were used to graft polymer onto surface of silica nanoaprticles. The investigation include:1. By condensation reaction of the hydroxyl groups on the surface of silica nanoparticle with coupling agent KH—560, epoxy groups were covalently attached to silica nanoparticles. The reversible addition—fragmentation—chain transfer (RAFT) agent, dithiobenzoate, was anchored on the surface of the silica nanoparticles via the reaction of carboxylic acid in the RAFT agent, carboxypropyl dithiobenzoate with the epoxy group. The resultant RAFT agent was used in the surface RAFT copolymerization of styrene (St) and maleic anhydride(MAh) at ambient temperature, and SiO₂/poly (St-afr-2MAh) hybrid materials were obtained. Since MAh is highly reactive, poly( ethylene oxide) methyl ether (MPEO) was grafted onto the copolymers on the surface of particles via reaction of hydroxyl group in MPEO with MAh, bio-compatible PEO-functionalized silica particles were obtained. This provides a new approach to graft biocompatible and hydrophilic PEO onto silica. 2. Polystyrene was grafted onto silica particles by surface RAFT polymerization, using dithiobenzoate anchored silica as RAFT chain transfer agent. The kinetics of surface RAFT polymerization was studied.3. A facile method for rapidly grafting high molecular weight polystyrene onto the surface of silica nanoparticles via ATRP was developed. By adding small amount of polystyrene which was synthesized by thermal radical polymerization of styrene, high molecular weight polystyrene was grown from the silica particles relatively fast. It was found that the rate of surface ATRP increased with the increase of polystyrene added. The possible reason for this phenomenon was explosed. The same phenomenon was observed in surface ATRP from carbon nanotubes.4. Surface-initiated ATRP of functional monomer, glycidyl methylacrylate (GMA) was investigated. First, the ATRP initiatior was attached to the surface of silica nanoparticles and then poly(glycidyl methylacrylate) was grafted onto the silica nanoparticles. Subsequently, the side epoxy group was transferred to amine by ring opening reaction of epoxy group in GMA unit with ethylenediamine. The resultant multiamine-functionalized silica particles absorbed Ag⁺ from the aqueous solution forming metal nanoparticles-loaded silica partilces composites after reduction of NaBH₄. TEM photo indicated that diameter of the silver nanoparticles was less than 10 nm, and XPS spectrum showed that silver nanoparticles were made of pure metallic silver, no other species were present.5. Poly(butyl acrylate) (PBA) was grafted onto the surface of silica nanoparticles by surface- initiated ATRP. The resultant PBA-g-SiO₂ hybrid particles were used to modify poly(vinyl chloride) (PVC). TEM photo indicated that hybrid particles were homogeneously dispersed in PVC matrix. The impact strength, tensile strength and maximum break elongation of nanocomposite materials were increased about 300, 40 and 30 percent, respectively and Vica soft points were apparently improved.