Chemical Grafting Method Research Articles

Covalently Attached, Silver-Doped Poly(vinyl alcohol) Hydrogel Films on Poly(l-lactic acid)

Covalently attached, soft poly(vinyl alcohol) (PVA) hydrogel films containing silver particles were prepared on solid biodegradable poly(l-lactic acid) (PLLA) samples by a multistep procedure involving oxygen plasma treatment, UV-initiated graft polymerization, and chemical grafting methods. The modification steps were followed and verified using attenuated total reflection infrared spectroscopy and X-ray photoelectron spectroscopy. 2-Hydroxyethyl methacrylate (HEMA) was graft polymerized from the surface of oxygen plasma-treated PLLA film samples and the alcohol functionality in the grafted polyHEMA chains was oxidized using pyridinium dichromate to obtain an aldehyde-rich surface. PVA was then grafted onto this surface using acid catalysis (acetal formation). The "freeze/thaw method" was used to form a PVA hydrogel layer that incorporated the covalently grafted PVA chains in the physically cross-linked gel. This composite film (PLLA-PVA(gel)) was doped with silver ions, which were reduced to silver using NaBH(4). Scanning electron microscopy of cross sections of PLLA-PVA(gel) indicates robust attachment of the PVA hydrogel layer to the PLLA film. PLLA-PVA(gel/Ag(0)) film samples exhibit both antibacterial and reduced cell adhesion properties due to the antibacterial properties of silver nanoparticles and high water content, respectively. This method provides a route to mechanically sound biodegradable materials with tunable soft material surface properties. Potential applications in tissue engineering and biomedical devices are envisioned.

3-(2-Hydroxyl-Ethyl)-1-Propylimidazolium Bromide Immobilized on SBA-15 as Efficient Catalyst for the Synthesis of Cyclic Carbonates via the Coupling of Carbon Dioxide with Epoxides

3-(2-hydroxyl-ethyl)-1-propylimidazolium bromide (HEPIMBr) was immobilized onto SBA-15, Al-SBA-15 mesoporous molecular sieves and SiO2 by chemical grafting method. The materials were characterized and used as catalysts for solvent-free synthesis of cyclic carbonates from CO2 and epoxides under relatively mild conditions. Among them, the HEPIMBr immobilized on SBA-15 performs the best, showing carbonate selectivity and yield of ca. 100% (120 °C, 2.0 MPa, 2 h). The catalyst is thermally stable and shows good reusability. Based on the experimental results, a plausible reaction mechanism has been proposed for the catalytic reaction. 3-(2-hydroxyl-ethyl)-1-propylimidazolium bromide (HEPIMBr) was immobilized on SBA-15 mesoporous molecular sieve by chemical grafting method. It was found the material shows high catalytic efficiency and good stability towards the cyclic carbonates synthesis via. Cycloaddition of CO2 to epoxides. Moreover, the catalyst can be easily separated from the product. A plausible reaction mechanism has been proposed for the catalytic action.

Effect of nano-Si3N4 surface treatment on the tribological performance of epoxy composite

To overcome the disadvantages generated by the loose nano-partilce agglomerates dispersed in polymer compos- ites, a chemical grafting method was applied to modify nano-Si3N4 by covalently bonding glycidyl methacrylate (GMA) onto the particles. The tribological behavior of the epoxy composite filled with nano-Si3N4 or GMA treated Si3N4 (Si3N4- g-PGMA) was studied using a ring-on-block wear tester under dry sliding, and the worn surface of the filled epoxy compos- ite and the surface roughness of the composites after the sliding wear test were investigated by SEM (scanning electron microscopy) and AFM (atomic force microscopy), respectively. In comparison to the composites filled with untreated nano-Si3N4 particles, the composites with the grafted nano-Si3N4 exhibit improved sliding wear resistance and reduced fric- tion coefficient owing to the chemical bonding at the filler/matrix interface.

Modified Sulfonated Poly(arylene ether sulfone) Membranes Prepared via a Radiation Grafting Method for Fuel Cell Application

Polymer modifications involving crosslinking and grafting by radiation have been widely researched for use in biopolymers, hydrogels, heat-resisting electric wires, vulcanization, polymer recycling, gas separation, and pervaporation membranes because of their advantages over traditional chemical crosslinking and grafting methods, including a catalyst-free reaction, post-modification at room temperature for solid polymers, and short modification times and steps. Various recent studies have also utilized radiation modification techniques to prepare proton exchange membranes (PEMs). PEMs are membranes which have the ability to selectively transfer protons generated by electrochemical reactions from the anode to the cathode in fuel cells. For this purpose, polymers having strong acidic functional group as proton carriers (e.g. sulfonic acid groups) have generally been used. There are two main strategies to introduce sulfonic acid groups into polymers. One is to introduce the groups directly to a polymer (post-sulfonation or polymersulfonation) and the other is to perform polymerization with a sulfonated monomer (monomer-sulfonation). To date, preirradiation and post-sulfonation methods, in which sulfonic acid groups are introduced after crosslinking or grafting non-sulfonated polymers by irradiation, have been used in radiation-induced processes of PEMs in order to prevent unfavorable membrane damage such as decomposition of sulfonic acid groups. However, this method has structural limitations for PEMs because the types of target polymer for irradiation are restricted to perfluorinated or partially fluorinated polymers and aliphatic polymers. In addition, crosslinking and grafting agents should have sites available for post-sulfonation. Whereas, few studies have been conducted on radiation-induced sulfonated polymers (post-irradiation method) despite the advantage that various types of polymers, prepared with various sulfonated and nonsulfonated monomers, can be used as a matrix for radiation modification. In this study, we investigated a post-irradiation method for PEMs and tried to improve PEM performance by preparing a radiation-grafted sulfonated polymer. Sulfonated polyarylene ether sulfone (SPAES) was used as a polymer matrix for irradiation. Here, the sulfonated polymer with a perfluorinated backbone (e.g. Nafion) was excluded due to its serious decomposition resulting from the chain scission effect caused by irradiation. Due to its additional acid group, acrylic acid was used as a grafting agent to increase the proton conduction properties of the resulting polymer.

Thin films of silica particles covered with lanthanide substituted Keggin polyoxometalates and their optical properties

In this paper, the chemical grafting method has been adopted to prepare hybrid core–shell particles by covering the surfaces of monodisperse uniform silica with lanthanides–polyoxometalates K a (EuXWO 39) 2 (X = Si, B, a = 13 or 15) shells, respectively. The thin films of core/shell polyoxometalates/silica particles were successfully fabricated by standard spin-coating method. The hybrid core–shell particles and thin films were characterized by IR, UV–vis spectra, scanning electron microscopy and luminescent spectra, respectively. The hybrid core–shell particles show the strong luminescence which could be seen by naked eyes. The excitation spectrum of thin film of polyoxometalate/silica particles show the ligand to metal charge transfer band, which could be not seen in the excitation spectrum of lanthanides–polyoxometalate. The ratios of the electronic dipole 5D 0 → 7F 2 transitions to the magnetic dipole 5D 0 → 7F 1 ones in the emission spectra of thin films have changed, which indicated the various symmetry of sites occupied by Eu 3+ ions in thin films.

Friction and wear behavior of the hybrid PTFE/cotton fabric composites filled with TiO2 nanoparticles and modified TiO2 nanoparticles

AbstractA chemical grafting method was applied to modify TiO2 nanoparticles through covalently introducing glycidoxypropyltrimethoxy silicane (KH560) followed by polyoxymethylene onto the particles to overcome the disadvantages generated by the agglomeration of nanoparticles. TiO2 nanoparticles unmodified and modified were introduced into hybrid polytetrafluoroethylene (PTFE)/cotton fabric composites. Friction and wear test demonstrated that TiO2 nanoparticles unmodified and modified can significantly increase the wear resistance of hybrid PTFE/cotton fabric composites but cannot reduce the friction coefficient. Fabric composites filled with grafted TiO2 nanoparticles exhibited a lower wear rate due to the disintegration of agglomeration and the improvement of interfacial adhesion between filler/matrix. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

Novel bifunctional NiMo/Al-SBA-15 catalysts for deep hydrodesulfurization: Effect of support Si/Al ratio

A series of Al-containing mesoporous molecular sieves SBA-15 with different Si/Al molar ratios (50, 30, 20 and 10) was prepared by chemical grafting method using aluminum(III) chloride as alumina source. Mo and NiMo catalysts prepared using Al-SBA-15 supports were tested in the 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization (HDS) reaction. The synthesized solids were characterized by N2 physisorption, small- and wide-angle XRD, Py FT-IR, 27Al MAS-NMR, temperature-programmed reduction (TPR), UV–vis diffuse reflectance spectroscopy (DRS), chemical analysis and HRTEM. It was found that post-synthetic alumination of SBA-15 by reacting with AlCl3 has a little influence on the ordered mesoporous structure of the parent SBA-15 and leads to amorphous silicoaluminate materials with moderate Bronsted acidity. For all Si/Al molar ratios studied, tetrahedrally coordinated Al3+ cations predominated over octahedrally coordinated ones. However, as Al loading increases, the proportion of the latter ones was also increased. The dispersion of oxidic and sulfided Mo species increases with the incorporation of aluminum in the SBA-15 support due to the strong interaction of Mo and Ni species with aluminum atoms which serve as anchoring sites on the support surface. Catalytic activity of Mo and NiMo/SBA-15 catalysts increased with Al incorporation in the support reaching a maximum at Si/Al molar ratio of 20. High activity of NiMo/Al-SBA-15 catalysts in 4,6-DMDBT HDS can be attributed to a good dispersion of Ni and Mo active phases and to the bifunctional character of these catalysts. It was shown that both types of sites, coordinatively unsaturated sites of NiMoS active phase and Bronsted acid sites of the support participate in the catalytic transformations of 4,6-DMDBT.

Effect of nano-Al2O3 surface treatment on the tribological performance of phenolic composite coating

To overcome the disadvantages generated by the loosened nano-particle agglomerates dispersed in polymer composites, a chemical grafting method was applied to modify nano-Al2O3 by covalently bonding toluene-2, 4-diisocyanate (TDI) onto the particles. The tribological behaviors of the phenolic composite coating filled with nano-Al2O3 or toluene-2, 4-diisocyanate treated Al2O3 (TDI-Al2O3) were studied using a ring-on-block wear tester under dry sliding, and the worn surfaces of the filled phenolic coating and transfer films formed on the surface of the counterpart ring sliding against the composite coating were investigated by SEM and optical microscope (OM), respectively. Owing to the effective improvement of the interfacial adhesion between the nano-Al2O3 and phenolic matrix, compared with the cases of untreated nano-Al2O3, the employment of TDI modified nano-Al2O3 (TDI-Al2O3) provided the phenolic coating with much higher tribological performance enhancement efficiency. Compared with other filled phenolic coating, 3 wt.% TDI-Al2O3 reinforced phenolic coating has the lowest frictional property and the highest wear resistance. Furthermore, we studied effect of sliding speed and applied load on the friction and wear behaviors of the phenolic coating filled with 3 wt.% nano-Al2O3 or TDI-Al2O3. The results showed that the friction coefficient of the composite coating reinforced with different fillers decreased with increasing sliding speed and applied load, and the anti-wear behavior of the coating filled with 3.0 wt.% TDI-Al2O3 was the best under 320 N and at a speed of 3.0 m/s. The investigations of the frictional surfaces showed that low content nano-Al2O3 or TDI-Al2O3 was able to enhance the adhesion of the transfer films of the phenolic coating to the surface of counterpart ring, so they significantly reduced the wear of the phenolic coating. FTIR and TGA analyses indicated that the surface of Al2O3 was coated with TDI through the covalent bond between the hydroxy groups of Al2O3 and –OCN groups of TDI.

A simple method to prepare poly(amic acid)-modified biomass for enhancement of lead and cadmium adsorption

A modified biomass of baker's yeast was prepared by grafting poly(amic acid), which was obtained via reaction of pyromellitic dianhydride (PMDA) and thiourea, onto the biomass surface at 50 °C for 4 h. This method was simpler than other reported chemical grafting methods. The presence of poly(amic acid) on the biomass surface was verified by FTIR, X-ray photoelectron spectroscopy (XPS) and microscope analyses, and the amount of carboxylate and amide groups in the biomass surface were found to be 1.36 and 0.7 mmol g −1 through potentiometric titration. Compared with the pristine biomass, the adsorption capacity of the modified biomass increased 15- and 11-fold for Cd 2+ and Pb 2+, respectively. According to the Langmuir equation, the maximum uptake capacities ( q m) for lead and cadmium were 210.5 and 95.2 mg g −1, respectively. The kinetics for cadmium and lead adsorption followed the pseudo-second-order kinetics. FTIR and XPS demonstrated that carboxyl, amide, and hydroxyl groups were involved in the adsorption of lead and cadmium, and the adsorption mechanism for the two metal ions included ion exchange, electrostatic interaction and complexation.

Graft polymerization onto inorganic nanoparticles and its effect on tribological performance improvement of polymer composites

To overcome the disadvantages generated by the loosened nanoparticle agglomerates dispersed in polymer composites, a chemical grafting method was applied to modify nano-alumina, silicon carbide and silicon nitride through covalently introducing polyacrylamide (PAAM) onto the particles. Sliding wear tests demonstrated that the frictional coefficient and specific wear rate of the nanoparticles/epoxy composites are lower than those of unfilled epoxy. Grafted nanoparticles reinforced composites have the lowest frictional property and the highest wear resistance due to the strengthening of the nanoparticle agglomerates and the enhancement of filler/matrix interfacial interaction resulting from the grafting polymers. Comparatively, graft treatment of nanoparticles is more beneficial to the improvement of the tribological features of the composites than the silane treatment that is used conventionally.