Gas phase grafting

Gas-Phase Grafting Liquid-Phase Grafting Deposition-Precipitation... 

Gas-phase grafting (GG) is characteristic in that gold can be deposited even on the acidic surfaces, such as activated carbon and on Si02 [27]. The vapor of gold acac complex is adsorbed on the support powder probably through the interaction of electron-rich oxygen atoms in acetylacetonate and then calcined in air to decompose it into metallic gold particles. 

Fig. 6.3. TEM image of Au/SiOj catalyst prepared by gas-phase grafting and calcined in air at 673 K for 4h. Black points are An particles (from [75])...

Table 1. Surface C atom hybridization and OML coverage ( 10%) for liquid phase and gas phase grafting on PLD and sputtered a-C films ( after Ar+ surface preparation)...

In contrast, gas phase grafting (GG) of dimethyl Au(III) acetylacetonate results in Au deposition both on Ti and on the Si02 surfaces, which causes p>oor selectivity to PO [24] (Table 14.2). 

The modihcation of polymer surfaces by graft copolymerization of a monomer or monomers from active sites has been reported in numerous references [165-169]. The most common techniques are y- and EB radiations, which generate surface radicals. Monomers can be present in gas phase (sublimed solid), in solution or as neat liquid. 

The first chiral phases introduced for gas chromatography were either amino acid esters, dipeptide, diamide or carbonyl-bis(amino acid ester) phases [721,724,756-758]. In general, these phases exhitdted poor thermal stability and are infrequently used today. Real interest and progress in chiral separations resulted from the preparation of diamide phases grafted onto a polysiloxane backbone. These phases were thermally stable and could be used to prepare efficient open tubular columns [734,756,758-762]. These phases are prepared from commercially available poly(cyano-propylmethyldimethylsiloxanes) or poly (cyanopropylmethylphenyl-... 

A heterogeneous olefin epoxidation catalyst containing both V and Ti in the active site was prepared by sequential non-hydrolytic grafting. The silica was exposed first to VO(OiPr)3 vapor followed by Ti(0 Pr)4 vapor. Formation of propene is evidence for the creation of Ti-O-V linkages on the surface. Upon metathesis of the 2-propoxide ligands with BuOOH, the catalyst becomes active for the gas phase epoxidation of cyclohexene. The kinetics of epoxidation are biphasic, indicating the presence of two reactive sites whose activity differs by approximately one order of magnitude. 

Two different approaches have been used to graft molybdenum on alumina, namely, either a two-step process involving gas-phase impregnation and further decomposition at high temperature (GPID) or the direct contact of [Mo(CO),5] vapor with the alumina support placed in a hot zone so as to achieve its decomposition. All of the relevant studies point to the existence of a close relationship between the OH group density on the support and the amount of deposited molybdenum as well as the chemical nature of such deposits. Hence, we successively deal with three types of alumina highly, partially and fully dehydroxylated surfaces. 

While photo-grafting of organic polymers is a fairly mature field, there is a need for more efficient photosensitizers. Convenient methods to graft onto natural fibers would be valuable for specialty fabrics as well as consumer products, particularly if the monomer can be delivered in the gas phase or as an aqueous solution. 

Heterogeneous diene polymerization catalysts based on modified and unmodified silica-supported lanthanide complexes are known as efficient gas-phase polymerization catalysts for a variety of support materials and activation procedures (see Sect. 9). Metal siloxide complexes M(()SiR3 )x are routinely employed as molecular model systems of such silica-immobilized/ grafted metal centers [196-199]. Structurally authenticated alkylated rare-earth metal siloxide derivatives are scarce, which is surprising given that structural data on a considerable number of alkylated lanthanide alkoxide and aryloxide complexes with a variety of substitution patterns is meanwhile available. 

Solution grafting has been the predominant approach for the immobilization of rare-earth metal precatalyst components [288]. The identification of the catalytically active surface species, commonly formed upon interaction with organoaluminum compounds, is difficult and assisted by molecular model complexes. Several types of support materials including magnesium chloride [289], silica [290], and organic (co-)polymers [291,292], were examined both in the gas-phase and the slurry polymerization of 1,3-dienes. 

Growth at polymer plasma interface. Deposition occurs by grafting of gas-phase material onto an activated surface. This could be particularly favoured if the grafted compound contained unsaturation. It is usually argued... 

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