Postgrafting of vinyl polymers onto hyperbranched poly(amidoamine)-grafted nano-sized silica surface

To prepare polymer-grafted nano-sized silica with hydrophilic core and hydrophobic shell and with higher percentage of grafting, the postgraft polymerization of vinyl polymers onto hyperbranched poly(amidoamine)-grafted (PAMAM-grafted) nano-sized silica initiated by the system consisting of Mo(CO)₆ and terminal trichloroacetyl groups of PAMAM-grafted silica was investigated. The introduction of trichloroacetyl groups onto PAMAM-grafted silica surfaces was readily achieved by the reaction of trichloroacetyl isocyanate with terminal amino groups of PAMAM-grafted silica. It was found that the polymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and glycidyl methacrylate (GMA) was successfully initiated by the system consisting of Mo(CO)₆ and terminal trichloroacetyl groups of PAMAM-grafted silica. In the polymerization, the corresponding vinyl polymers were effectively postgrafted onto PAMAM-grafted silica, based on the propagation of polymer from surface radicals formed by the reaction of terminal trichloroacetyl groups with Mo(CO)₆: the percentage of PMMA postgrafting onto PAMAM-grafted silica reached to 400% after 30 min, but the formation of gel was observed after 35 min. The formation of gel tends to decrease by use of hyperbranched PAMAM-grafted silica with higher percentage of grafting. The vinyl polymer-postgrafted nano-sized silica gave a stable colloidal dispersion in various organic solvents.     

Grafting of vinyl polymers onto VGCF surface and the electric properties of the polymer-grafted VGCF

The graft polymerization of vinyl monomers onto vapor grown carbon fibers (VGCF) initiated by the system consisting of molybdenum hexacarbonyl (Mo(CO)₆) and trichloroacetyl (COCCl₃) groups introduced onto the surface was investigated. The introduction of trichloroacetyl groups onto VGCF surface was successfully achieved by the reaction of carboxyl groups on VGCF surface with trichloroacetyl isocyanate. It was found that the radical graft polymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and glycidyl methacrylate (GMA) is successfully initiated by the system consisting of Mo(CO)₆ and COCCl₃ groups introduced onto the surfaces. In the polymerization, the corresponding vinyl polymers were effectively grafted onto the VGCF surface, based on the propagation of polymer from surface radicals formed by the interaction of trichloroacetyl groups and Mo(CO)₆: the percentage of PMMA grafting reached 40%. Polymer-grafted VGCF gave a stable colloidal dispersion in good solvents for grafted polymer. The electric resistance of composite prepared from the polymer-grafted VGCF suddenly increased in organic solvent vapor over 10³ times, and returned to initial resistance when it was transferred into dry air. These results indicate that such composites can be used as novel gas sensors.     

Grafting of branched polymers onto the surface of vapor grown carbon fiber and their electric properties

The grafting of branched polymers onto vapor grown carbon fiber (VGCF) surface and their electric properties of the composite prepared from the branched polymer-grafted VGCF were investigated. In the first step, the grafting of copolymers having pendant peroxy groups onto VGCF was achieved by the copolymerization of 1-(t-butylperoxy-i-propyl)-3-i-propenylbenzene (BPPB) with vinyl monomers initiated by the system consisting of Mo(CO)₆ and trichloroacetyl groups previously introduced onto the surface. In the second step, the postpolymerization of vinyl monomers was initiated by pendant peroxy groups of grafted poly(vinyl monomer-co-BPPB) on the surface to give branched vinyl polymer-grafted VGCF. The dispersibility of VGCF in THF was remarkably improved by grafting of branched polymers onto the surface. The electric resistance of composites prepared from the branched polymer-grafted VGCF suddenly increased when the composites were transferred into solvent vapors and suddenly decreased when they were transferred to dry air.     

Surface grafting of polymers onto aramid powder: graft polymerization of vinyl monomers initiated by azo groups introduced onto the surface of aramid powder

The radical graft polymerization of vinyl monomers onto the surface of aramid powder, i.e., poly(p-phenylene terephthalamide) powder, initiated by azo groups introduced onto the surface was investigated. The introduction of azo groups onto the aramid surface was achieved by the reaction of surface acyl chloride groups, which were introduced by the treatment of aramid powder with adipoyl dichloride, with 2,2′-azobis[2-(2-imidazolyn-2-yl)propane] in the presence of pyridine: the amount of azo groups thus introduced onto the surface was determined to be 0.57 mmol/g by elemental analysis. It was found that the polymerizations of methyl methacrylate (MMA) and styrene were successfully initiated by the azo groups on the surface and that the corresponding polymers were grafted onto the surface. The percentage of surface grafting of polystyrene and poly(methyl methacrylate) (PMMA) increased up to 37.6 and 26.5%, respectively. Thermogravimetric analysis of polymer surface-grafted aramid powder confirmed that the grafting of polymers is limited on the surface. The polymerization rate was found to bear a first-order dependence on the concentration of aramid powder having azo groups. This suggests that in graft polymerization, unimolecular termination preferentially proceeds.     

Surface grafting of polymers onto glass plate: Polymerization of vinyl monomers initiated by initiating groups introduced onto the surface

The surface grafting of polymers onto a glass plate surface was achieved by the polymerization of vinyl monomers initiated by initiating groups introduced onto the surface. Azo groups were introduced onto the glass plate surface by the reaction of 4,4′-azobis(4-cyanopentanoic acid) with isocyanate groups, which were introduced by the treatment with tolylene-2,4-diisocyanate. The radical polymerization of various vinyl monomers was initiated by azo groups introduced onto the glass plate surface and the corresponding polymers were grafted from the surface: The surface grafting of polymers was confirmed by IR spectra, and the contact angle of surface, with water. The contact angle of the glass plate increased by the grafting of hydrophobic polymers, but decreased by the grafting of hydrophilic polymers. The radical postpolymerization was successfully initiated by the pendant peroxycarbonate groups of grafted polymer on the surface to give branched polymer-grafted glass plate. The cationic polymerization of vinyl monomers was also successfully initiated by benzylium perchlorate groups introduced onto the glass plate surface and the corresponding polymers were grafted onto the surface. The contact angle of the glass plate surface obtained from the cationic polymerization of styrene was larger than that obtained from the radical polymerization. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2165–2172, 1997     

Titanium-based solid catalysts for transesterification of methyl-methacrylate by 1-butanol: the homogeneous catalysis contribution

Titanium-based solid catalysts were prepared according to two different procedures. In order to improve the stability of the SiOTi bond in the titanium grafted silica catalysts, the surface remaining hydroxyl groups were passivated to prevent the titanium leaching by SiOTi bond solvolysis. This was performed by grafting trimethoxy-silane groups on isolated silanols of silica, after or before metal grafting. The synthesised materials were characterised by FT-IR spectroscopy, and their catalytic properties evaluated in the reaction of transesterification of methyl-methacrylate (MMA) with 1-butanol (BuOH) in liquid phase to produce butyl-methacrylate (BuMA). An important titanium leaching (18–35%) was always detected with all the solid catalysts.

Investigation of the behaviour of Ti(OBu)₄ as homogeneous catalyst for very small concentrations of titanium was carried out in order to evaluate the catalytic contribution of the active dissolved species. We demonstrate here that the catalytic activity is mainly due to the homogeneous catalysis.     

Surface grafting of polymer onto carbon thin film

The surface grafting of polymers onto carbon thin film deposited on a glass plate was achieved by two methods: the graft polymerization initiated by initiating groups introduced onto the surface; and the trapping of polymer radicals by surface aromatic rings of the thin film. It was found that the radical and cationic graft polymerization of vinyl monomers are initiated by azo and acylium perchlorate groups introduced onto the surface, respectively, and the corresponding polymers are grafted onto the surface: the surface grafting of polymers were confirmed by the contact angle of the surface with water. In addition, the anionic ring-opening alternating copolymerization of epoxides with cyclic acid anhydrides was found to be initiated by potassium carboxylate groups on the carbon thin film to give the corresponding polyester-grafted carbon thin film. On the other hand, polymer radicals formed by the decomposition of azo polymer, such as poly(polydimethylsiloxane-azobiscyanopentanoate) and poly(polyoxyethylene-azobiscyanopentanoate), were successfully trapped by the surface aromatic rings of carbon thin film and polydimethylsiloxane and polyoxyethylene were grafted onto the surface. © 1995 John Wiley & Sons, Inc.     

PHOTOCATALYTICALLY INDUCED DYE DECOLOURISATION IN AN UNSUPPORTED THIN FILM REACTOR

Aqueous solutions of the dye indigo carmine were decolourised following ultraviolet (UV) irradiation in the form of thin liquid films in the presence of the semi-conductoi photocatalyst, titanium dioxide, Ti02. These films, which were unsupported and totally enclosed, are commonly referred to as liquid “bells” and were generated using a nozzle of special design. Decolourisation rates were increased as the concentration of Ti0₂ was increased from 0.74 to 11.8 g/l. Addition of hydrogen peroxide, H₂0₂, in concentrations ranging from 1.07 to 8.53 g/l at a fixed Ti0₂ concentration of 1.47 g/l also resulted in increased rates of decolourisation. The rate of disappearance of the indigo carmine was assumed to follow first order kinetics whereas the influence of the two other species, Ti02 and H202, was accounted for by a power law model. The exponents for this model, obtained from an analysis of the experimental data, were 0.8 and 0.2 for, respectively Ti0₂ and H₂0₂.     

Grafting of branched polymers onto nano-sized silica surface: Postgrafting of polymers with pendant isocyanate groups of polymer chain grafted onto nano-sized silica surface

To control the surface wettability of nano-sized silica surface, the postgrafting of hydrophilic and hydrophobic polymers to grafted polymer chains on the surface was investigated. Polymers having blocked isocyanate groups were successfully grafted onto nano-sized silica surface by the graft copolymerization of methyl methacrylate (MMA) with 2-(O-[1′-methylpropylideneamino]caboxyamino)ethyl methacrylate (MOIB) initiated by azo groups previously introduced onto the surface. The blocked isocyanate groups of poly(MMA-co-MOIB)-grafted silica were stable in a desiccator, but isocyanate groups were readily regenerated by heating at 150 °C. The hydrophilic polymers, such as poly(ethylene glycol) (PEG) and poly(ethyleneimine) (PEI), were postgrafted onto the poly(MMA-co-MOIB)-grafted silica by the reaction of functional groups of PEG and PEI with pendant isocyanate groups of poly(MMA-co-MOI)-grafted silica to give branched polymer-grafted silica. The percentage of grafting increased with increasing molecular weight of PEG, but the number of postgrafted chain decreased, because of steric hindrance. The hydrophobic polymers, such as poly(dimethylsiloxane) were also postgrafted onto poly(MMA-co-MOI)-grafted silica. It was found that the grafting of hydrophobic polymer and the postgrafting of hydrophilic polymer branches readily controls the wettability of silica surface to water.     

A model catalyst approach to the effects of the support on Co–Mo hydrodesulfurization catalysts

Co–Mo model sulfide catalysts, in which CoMoS phases are selectively formed, were prepared by means of a CVD technique using Co(CO)₃NO as a precursor of Co. It is shown by means of XPS, FTIR and NO adsorption that CoMoS phases form selectively when the Mo content exceeds monolayer loading. A single exposure of MoS₂/Al₂O₃ to a vapor of Co(CO)₃NO at room temperature fills the edge sites of the MoS₂ particles. It is suggested that the maximum potential HDS activity of MoS₂/Al₂O₃ and Co–Mo/Al₂O₃ catalysts can be predicted by means of Co(CO)₃NO as a “probe” molecule. An attempt was made to determine the fate of Co(CO)₃NO adsorbed on MoS₂/Al₂O₃. The effects of the support on Co–Mo sulfide catalysts in HDS and HYD were investigated by use of CVD-Co/MoS₂/support catalysts. XPS and NO adsorption showed that model catalysts can also be prepared for SiO₂-, TiO₂- and ZrO₂-supported catalysts by means of the CVD technique. The thiophene HDS activity of CVD-Co/MoS₂/Al₂O₃, CVD-Co/MoS₂/TiO₂ and CVD-Co/MoS₂/Al₂O₃ is proportional to the amount of Co species interacting with the edge sites of MoS₂ particles or CoMoS phases. It is concluded that the support does not influence the HDS reactivity of CoMoS phases supported on TiO₂, ZrO₂ and Al₂O₃. In contrast, CoMoS phases on SiO₂ show catalytic features characteristic of CoMoS Type II. With the hydrogenation of butadiene, on the other hand, the Co species on MoS₂/TiO₂, ZrO₂ and SiO₂ have the same activity, while the Co species on MoS₂/Al₂O₃ have a higher activity.     

Differential scanning calorimetry study of linseed oil cured with metal catalysts

Differential scanning calorimetry (DSC) has been used to study the autoxidative curing process of linseed oil catalyzed by conventional metal driers and two metal sol-gel precursors, Ti(Oi-Pr)₂(acac)₂ and Ti(Oi-Pr)₄, at elevated temperatures. Linseed oil resins with a range of 0–5.0 wt.% metal sol-gel precursor and 0–9.0 wt.% zirconium dric have been investigated by both dynamic and isothermal methods. The onset, peak and end temperatures of the reaction exotherms were observed as a function of metal catalyst type and content. The Borchardt and Daniels kinetics method was used to quantify the heat of reaction of the dynamic DSC scans. The indention hardness of the resultant coatings in the DSC sample pans was measured as an indication of crosslink density. The inclusion of small quantities of metal catalyst (0–5.0 wt.% titanium alkoxide, 0–2.0 wt.% zirconium drier) caused the reaction exotherm to broaden and shift to lower temperatures. At higher metal catalyst content (>5.0 wt.% Ti(Oi-Pr)₂(acac)₂ or 5.0 wt.% Ti(Oi-Pr)₄) the reaction exotherms became imperceptible. Overall, as the metal catalyst content was increased, the heat of reaction decreased while indention hardness increased. The effects of the two sol-gel precursors on the reaction exotherms were similar to the effects of conventional driers. Combinations of conventional driers were also studied.     

Grafting and crosslinking reaction of carboxyl-terminated liquid rubber with silica nanoparticles and carbon black in the presence of Sc(OTf)3

The grafting of carboxyl-terminated liquid rubbers, specifically polybutadiene (BR-COOH) and nitrile rubber (NBR-COOH), was investigated in the presence of scandium trifluoromethanesulfonate (Sc(OTf)₃) as a catalyst, on silica nanoparticles and on carbon black surfaces. In the absence of the catalyst, the grafting of the liquid rubbers onto silica nanoparticles and carbon black minimally proceeded. In contrast, terminal-carboxyl groups of the liquid rubbers readily reacted with amino groups on silica and phenolic hydroxyl groups on carbon black in the presence of Sc(OTf)₃ to give BR-grafted and NBR-grafted silica and carbon black. After the grafting reaction, Sc(OTf)₃ was easily recovered and the recovered Sc(OTf)₃ could be reused in the grafting of the liquid rubbers onto silica and carbon black. In addition, when an excess of silica nanoparticle and carbon black was reacted in the absence of solvent, the crosslinking reactions of the liquid rubbers by silica nanoparticles and carbon black proceeded in the presence of Sc(OTf)₃.     

Effect of potassium on the catalytic activity of TS-1

Titanium silicate-1 (TS-1) samples contained a significant amount of potassium derived from contaminants in an aqueous solution of Pr₄NOH. By washing with H₂SO₄, the alkali-exchanged sites were converted to sites with two OH groups or ‘closed’ Ti(OSi)₄ sites. Treatment of the acid-washed samples with an aqueous solution of K₂CO₃ led to the incorporation of potassium with a K/Ti ratio of around unity, suggesting that K ion exchange on TS-1 corresponds to the presence of Ti in the framework. The potassium ion exchange is considered to occur mainly on the Si–OH group adjacent to the ‘open’ Ti site. The presence of potassium retarded the oxidation of organic compounds with aqueous H₂O₂ to a different extent depending on the substrates. The retarding effect decreased in the order hexane>2-hexene>2-penten-1-ol and there was little inhibition in the oxidation of 2-penten-1-ol. This could be interpreted in terms of polarities of substrates and active sites in TS-1; non-polar hexane was less easily accessible to the Ti environment made more polar by adjacent potassium. In a similar manner, promotion of the oxidation of the alcoholic group in the reaction of 2-penten-1-ol over the K-type TS-1 might be ascribed to increased interaction of the alcoholic group with the active Ti site.     

Use of mesoporous SBA-15 for nanostructuring titania for photocatalytic applications

SBA15–TiO₂ samples prepared by introducing titanium with a grafting method and having TiO₂ loadings below 15 wt.% have been characterized by XRF, XRD, IR, porosimetry, SEM, HRTEM, and UV–Visible diffuse reflectance. Differently from the samples reported in the literature characterized by a high TiO₂ loading, no evidences have been found for the presence of titania particles inside or outside the mesopores of SBA-15. Three different titanium species were instead evidenced to be present. The first two derive from the reaction of titanium with silanol groups in the corona area of inner SBA-15 walls leading to the formation of either TiO₄ tetrahedral sites (by reaction by hydroxyl nests of surface defect sites) and/or pseudo-octahedral surface sites anchored by two (or more) Si or Ti ions through bridging oxygens. The third species derives from the reaction of titanium in the regions with high sylanol density, e.g. in the micropores located in the corona of SBA-15 channels, leading to the formation of TiO₂-like nanoareas (probably Si-doped) with dimensions of around 1–2 nm maximum. The potential interest of these materials as photocatalysts, for the presence of a TiO₂-like nanoareas highly accessible by reactants, is discussed.     

Pt/TiO_2催化二甲醚部分氧化重整制氢

二甲醚是一种理想的氢载体,可用于解决氢的储存和运输。以Pt/TiO_2为部分氧化催化剂,结合Ni/Al_2O_3重整催化剂,考察钛前驱体和焙烧温度对二甲醚部分氧化重整制氢反应的影响。结果表明,以Ti(C4H9O)4为原料制备的TiO_2为金红石相,Ti(SO4)2或Ti O(OH)2为原料制备的TiO_2为锐钛矿相;以Ti(C4H9O)4为原料制备的Pt/TiO_2-E催化剂催化性能略好,转化率接近100%,H2收率约90%,表明金红石相TiO_2负载的Pt催化剂略佳;以Ti(SO4)2为原料制备的Pt/TiO_2-S催化剂500℃焙烧可获得金红石相TiO_2。与Pt/Al_2O_3催化剂相比,Pt/TiO_2催化剂具有更好的催化性能,H2收率超过90%,而Pt/Al_2O_3催化剂H2收率约80%。     

Characterization of Mo–Sn–O system by means of Raman spectroscopy and electrical conductivity measurements

Mo–Sn–O systems were characterized by Raman spectroscopy and electrical conductivity measurements. The catalysts were obtained from precipitation of SnCl₄ by ammonia in the presence of (NH₄)₂Mo₇O₂₄ using four different levels of Mo concentration. The electrical conductivity measurements showed that particles are formed by agglomeration of SnO₂ crystals aggregated by polymolybdate. Raman spectroscopy suggested that four-coordinated species are dispersed at the external surface while six-coordinated species are inside the particles. For high Mo concentration (Mo >10%), octahedral coordinated species are also on the surface. Bulk MoO₃ oxide was not observed. These results confirm the model previously proposed.     

Gold catalysts supported on mesoporous titania for low-temperature water–gas shift reaction

Mesoporous titania with high surface area and uniform pore size distribution was synthesized using surfactant templating method through a neutral [C₁₃(EO)₆–Ti(OC₃H₇)₄] assembly pathway. The different gold content (1–5 wt.%) was supported on the mesoporous titania by deposition–precipitation (DP) method. The catalysts were characterized by X-ray diffraction, TEM, SEM, N₂ adsorption analysis and TPR. The catalytic activity of gold supported mesoporous titania was evaluated for the first time in water–gas shift reaction (WGSR). The influence of gold content and particle size on the catalytic performance was investigated. The catalytic activity was tested at a wide temperature range (140–300 °C) and at different space velocities and H₂O/CO ratios. It is clearly revealed that the mesoporous titania is of much interest as potential support for gold-based catalyst. The gold/mesoporous titania catalytic system is found to be effective catalyst for WGSR.     

Structure–activity relationships in alumina-supported molybdena–vanadia catalysts for propane oxidative dehydrogenation

The interactions between Mo and V on alumina are studied for the oxidative dehydrogenation (ODH) of propane. Dispersed surface molybdena and vanadia species share alumina support but show no interaction below Mo + V monolayer coverage. Vanadia and molybdena species react on alumina into mixed Mo–V–(Al)–O above Mo + V monolayer coverage, which nature depends on environmental conditions. Molybdena sites may form Al₂(MoO₄)₃ or Mo–V–O phases depending on loading and temperature. The Mo–V–O phases spread on the support as separate surface oxides at lower coverage, such trend appears promoted by ODH reaction conditions.     

Various approaches to transfers improvement during biphasic catalytic hydroformylation of heavy alkenes

The [HRh(CO)(TPPTS)₃] precursor, where TPPTS is the water-soluble P(m-C₆H₄SO₃Na)₃ ligand, has opened a large area for the Supported-Aqueous-Phase (SAP) catalysed functionalisation of heavy substrates. We investigated several ways to increase the efficiency of heavy alkenes hydroformylation by [Rh₂(μ-S^tBu)₂(CO)₂(TPPTS)₂]. Addition of a cosolvent was shown to lead to a significant leaching of rhodium in the organic phase. Promising results were obtained. First, the Delmas–Chaudhari method of adding small amounts of PPh₃ to [HRh(CO)(TPPTS)₃] to maintain the complex at the interface, was examined for [Rh₂(μ-S^tBu)₂(CO)₂(TPPTS)₂]. Here [Rh₂(μ-S^tBu)₂(CO)₂(PPh₃)₂] was rapidly formed and is operating classically in the organic phase. Moreover, β-cyclodextrin was used as a phase-transfer agent allowing the inclusion of the substrate and its transport to the aqueous phase where the reaction is occurring. Finally, the use of silica with various hydration ratios in SAP catalysis led us to propose that the microreactors containing water, complex and extra TPPTS operate on the surface of the support.     

Niobium sulfide as a dopant for Mo/TiO2 catalysts

Mo/TiO₂ catalysts were modified with Nb by two different methods, sol–gel and surface deposition, in order to study the effect of Nb incorporation on the thiophene HDS activity. The results show that the formation of Nb–Ti mixed oxides leads to catalysts with poor HDS activity while the deposition of Nb oxide species on the surface of TiO₂ leads to catalysts with activities larger than those of Mo/Al₂O₃ and Mo/TiO₂. This increase in activity was attributed to the formation of a larger population of Mo sulfur anionic vacancies when Nb was surface deposited on the TiO₂.