Covalent grafting of polyacrylamide onto mesoporous MCM-41 silica via free radical polymerization (original) (raw)
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Microporous and Mesoporous Materials [Working Title]
Mesoporous silica nanoparticles (MSNs) are widely studied and are an interesting material due to its application in wide range of areas, for example, in drug delivery, catalysis, in sensors, and in adsorption and separation. Specifically, MSNs contain high surface area and large pore volume, providing high drug loading capacity, tunable pore size, surface chemistry for accommodation of a variety of guest molecules, and versatile functionalization on the external and internal surface for a broad spectrum of applications. Many new strategies have been developed for the synthesis and functionalization of mesoporous silica-based materials. The functionalization of MSNs is highly important as it leads to the development of new chemical and physical properties. Thus, preparation of these organic/inorganic hybrid structures requires facile and controlled techniques to generate enhanced properties. The grafting of polymers using controlled radical polymerization (CRP) techniques has turned out to be the best suited method to synthesize these well-defined organicinorganic hybrid MSNs. Most common polymerization techniques are atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide mediated polymerization (NMP). This chapter will be highlighting the state-of-the-art techniques for the synthesis of variety of MSNs, its functionalization using CRP techniques, and application of polymer functionalized MSNs.
Polymer Journal, 1989
Radical graft polymerization from ultrafine silica surface was investigated. A redox system consisting of eerie ion and the silica particles carrying reducing groups, such as alcoholic hydroxyl, amino, and mercapto groups, was capable of initiating the radical polymerization of acrylamide (AAm). The introduction of alcoholic hydroxyl groups onto the surface was achieved by the treatment of the silica with 3-glycidoxypropyltrimethoxysilane in acidic condition in water. Amino or mercapto groups were introduced onto the silica by reactions of surface silanol groups w.ith 3-aminopropyltriethoxysilane or 3-mercaptopropyltrimethoxysilane, respectively. The initiating ability of the redox system changed, depending on the reducing groups on the silica surface, in the following order: alcoholic hydroxyl group< amino group< mercapto group. In the above redox polymerization, polyacrylamide was grafted onto the silica based on the propagation of the polymer from the radicals formed by the reaction of eerie ion with alcoholic hydroxyl, amino, or mercapto groups. The percentage of grafting onto the silica reached about 25%. The silica obtained from the redox graft polymerization gave a stable colloidal dispersion in water.
Development of pH-responsive polymer-grafted mesoporous silica
Transactions of the Materials Research Society of Japan, 2013
The drug delivery material was developed from mesoporous silica grafted with pH-responsive poly (acrylic acid) (PAA). The mesoporous silica was prepared from rice husk ash via the surfactant assisted sol-gel method, obtaining the 2D hexagonal porous structure. PAA was grafted on mesoporous silica surface by UV-induced graft polymerization. The irradiation time and monomer concentration on the graft polymerization were investigated and the results revealed that increasing the irradiation time as well as the monomer concentration enhanced the grafting percentage due to an increase in the extent of polymerization. Finally, the loading and releasing behaviors of Indigocarmine as drug model from the PAA-grafted mesoporous silica studied at various pHs. The PAA-grafted mesoporous silica showed slower drug releasing as increasing the grafting amount.
Macromolecules, 2004
Polymer chains are grafted from silica beads (colloidal sol in dimethylacetamide) by atom transfer radical polymerization (ATRP). The method consists of grafting first the initiator molecules on the silica surface ("grafting from" method), in two steps. First, thiol-functionalization of the surface was achieved via silanization with a mercaptopropyl triethoxysilane. Second, we performed an overgrafting of the surface by reacting the thiol with 2-bromoisobutyryl bromide to generate the halogen-functional ATRP initiator. From that, the polymerization of styrene was conducted. Control of both the molecular weight and the density of grafted chains can be achieved by this method. The other originality of this work is that we keep the nanoparticles in solution at each stage of the procedure (even during the purification steps), as this is the only way to avoid irreversible aggregation. The state of dispersion of the grafted nanoparticles is followed by small-angle neutron scattering. Characterizations such as gel permeation chromatography, 29 Si CP/MAS NMR, elemental analysis, infrared spectroscopy, and thermogravimetric analysis are conducted to confirm the success of the grafting reaction.
Journal of Colloid and Interface Science, 2003
A range of polyelectrolyte-grafted silica particles have been prepared by grafting suitable initiators onto near-monodisperse, 304-nmdiameter silica particles using siloxane chemistry, followed by surface-initiated atom transfer radical polymerization (ATRP) of four ionic vinyl monomers, namely sodium 4-styrenesulfonate (SStNa), sodium 4-vinylbenzoate (NaVBA), 2-(dimethylamino)ethyl methacrylate (DAM), and 2-(diethylamino)ethyl methacrylate (DEA) in protic media. The resulting polyelectrolyte-grafted silica particles were characterized using dynamic light scattering (DLS), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), helium pycnometry, and diffuse reflectance infrared Fourier transfer spectroscopy (DRIFTS). The TGA results indicated that the polyelectrolyte contents of the silica particles could be varied from 0.6% to 6.0% in weight. SEM studies revealed several surface morphologies for the grafted polyelectrolytes and XPS analysis of the particle surface also provided good evidence for surface grafting. Combined aqueous electrophoresis and DLS studies confirmed that these polyelectrolyte-grafted silica particles had pH-dependent colloid stabilities, as expected. Cationic polyelectrolyte-grafted silica particles were colloidally stable at low or neutral pH, but became aggregated at high pH. Conversely, anionic polyelectrolyte-coated silica particles became unstable at low pH. It was found that the rate of surface-initiated ATRP was substantially slower than the analogous solution polymerization. Finally, there was some evidence to suggest that, at least in some cases, a significant fraction of polymer chains became detached from the silica particles during polymerization.