Indirect grafting

The two main immobilisation techniques on a mesoporous material are direct grafting and indirect grafting (tethering), as shown in Scheme 1. In the former case, the complex interacts directly with the matrix. In the latter case, the complex is tethered to the supporting material via a spacer ligand, which is either introduced first on the support (as shown on the upper part of Scheme 1) or integrated into the complex before being anchored onto the support (lower part of Scheme 1). 

Scheme 1 Schematic drawing of direct and indirect grafting...

Another important paper on indirect grafting was due to Sakurada and co-workers (26) who did an extensive work on the composition of the styrene... 

By chemical agents, indirect grafting on Nylon in liquid phase is frequently referred to in the bibliography. The most common reagent is air (144) or ozone, under controlled conditions, in order to avoid deterioration on the mechanical properties of the fiber, which is then immersed in the monomer. Hence, styrene (145-149), vinylidene chloride (146), vinyl acetate (146), acrylic and methacrylic acids (149), methyl methacrylate (146), acrylonitrile (146,148,149), 2-methyl-5-vinylpyridine (149) were successfully employed as grafting comonomers. 

N-Halogenation as the preliminary step of indirect grafting on polyamide backbone is another interesting method which was studied with good results by Bamford and co-workers (150). The N-chlorination was undertaken by immersion for several minutes at room temperature in an aqueous solution of sodium hypochlorite to which acetic acid was added until reaching pH 4—4.5, followed by washing with distilled water and drying in vacuum at 40° C. N-Bromination... 

An anionic technique by indirect grafting was proposed for N-metallation of Nylon by Yamaguchi (153-155), in which alcali metals dissolved in liquid ammonia displace the amidic hydrogen atoms. Nylon derivatives and graft copolymers can be synthetized from the N-metallated Nylon (153). For ethylene oxide as grafting monomer, the metallated fibers were soaked in a tetrahydro-furan solution of the monomer, at 60° C (154). Methyl methacrylate is grafted on Nylon with a conversion over 90% by this technique (155). Other procedures involve the use of sodium methoxide in methanol solution and subsequent anionic graft copolymerization of acrylonitrile in a tetrahydrofuran solution (156). 

Indirect grafting is reported for vinyl acetate on Nylon 6 which had been preirradiated with UV light (194). 

Berisha, A., C. Combellas, F. Kanoufi, J. Pinson, S. Ustaze, and F. I. Podvorica. Indirect grafting of acetonitrile-derived films on metallic substrates. Chem. Mater. 22, 2010 2962-2969. 

Both R8 and 804 directly or indirectly initiate polymerization. It was observed that the percentage of grafting of MA onto reduced wool was higher than in wool. This suggested that the additional —8H groups provide sites for grafts [45]. 

Indirect pathway. Recipient APCs migrate into the graft and phagocytize alloantigens. The donor MHC molecules then are expressed on the cell surfaces of the recipient s APCs and presented to recipient T cells in the lymph nodes. 

The formation of appreciable quantities (up to "oQ0% based on the initial additive concentration) of the grafted substituted hydroxylamine O W0PP as from reaction 7) in photo-degrading PPH can be demonstrated by indirect methods (10, 11). For example after the rapid loss of the initial concentration of a piperidine or its nitroxide in PPH film, heating the film immersed in isooctane for several hours at 100 C in the presence of oxygen causes the re-appearance of nitroxide in appreciable quantities as measured by e.s.r. spectroscopy (ll). This nitroxide most likely results from a reaction analogous to reaction 8 (l2). In addition we have observed the ) N-0-C band (at 1306 cm 1) in the infrared spectrum of irradiated, nitroxide-containing PP films by Fourier Transform IR spectroscopy (ll)., ... 

It is known that some spinel-structured 3d-metal oxides are good catalysts for many processes involving electron transfer [12]. However, their low conductivity does not allow for the direct use in the electrode of the battery, and grafting them onto the carbon matrix is also very difficult technical problem. It was found recently that this problem could be solved indirectly, creating the spinel catalytic centers on the surface of carbon by means of adsorption of some 3d-metal complexes on the graphite surface followed by subsequent pyrolysis at certain temperatures [13,14],... 

Acrylonitrile and other olefinic monomers can be grafted on polycaprolactam by an indirect method in which the polyamide powder is first submitted to nitro-sation with dinitrogen trioxide and then bulk polymerized at 60° C (12). 

Such graft polymers, which virtually contain all the poly (vinyl chloride) in a grafted condition, can be crosslinked easily with peroxides via the EVA copolymer chains. This corresponds to an indirect statement on the degree of grafting of the products. 

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