Graft method

In its simplest form the direct grafting method involves the irradiation of polymeric substrate in the absence or presence of oxygen. Graft copolymerization of the monomer to the polymer is then initiated through the free radicals generated in the latter. The reaction can be schematically written as ... 

Anionic grafting methods (vide infra) can be applied to the synthesis of comb-shaped polymers. As an example, a polystyrene backbone is partially chloromethylated (under mild conditions) and used as an electrophilic deactivator for a living polystyrene 89). The grafting onto process yields well defined species that have been characterized accurately. The branches are distributed randomly along the backbone 90). 

The Rh complexes (cod)Rh[ jt-OSi(0 Bu)3] 2 and (nbd)Rh[ jt-OSi (0 Bu)3] 2 thermally decompose primarily via loss of HOSi(O Bu)3 and formation of Rh metal particles, rendering them ineffective for use as precursors to Rh/Si/0 materials however, these complexes are potentially useful as sources of Rh nanoparticles or site-isolated Rh species via grafting methods [99]. 

The continued development of new single-source molecular precursors should lead to increasingly complex mixed-element oxides with novel properties. Continued work with grafting methods will provide access to novel surface structures that may prove useful for catalytic apphcations. Use of molecular precursors for the generation of metal nanoparticles supported on various oxide supports is another area that shows promise. We expect that the thermolytic molecular precursor methods outlined here will contribute significantly to the development of new generations of advanced materials with tailored properties, and that it will continue to provide access to catalytic materials with improved performance. 

After a few minutes irradiation with a high pressure mercury lamp at about 50 C, a rather complete cover of grafted acrylic acid, acrylamide and other vinyl monomers could be obtained. In later experiments a continuous grafting method has been developed where a tape or a fiber bundle after suitable pretreatment is grafted by UV irradiation for a few seconds. Homopolymer formed is removed by washing and grafted polymer analyzed by dye absorption, IR reflection and ESCA spectroscopy. 

Direct hydrothermal synthesis. Prepared using titanium isopropoxide (triethanolaminato) and TEOS as the sources of Ti and Si, respectively, and the Gemini-type surfactant 18-12-18 or cetyl-benzyl dimethylammonium chloride (CBDAC) as a template. In the grafting method, silicious MCM-48 first prepared and then the dry surface grafted with titanium isopropoxide... 

Ti-SBA-15 Grafting method. SBA-15 prepared first using the amphiphilic triblock copolymer poly(ethyleneox-ide) -poly (propyleneoxide) -poly (ethyleneoxide) (EO-PO-EO) as template and TEOS as Si source. The composition was 2 g copolymer 0.021 mol TEOS 0.12 mol HC1 3.33 mol H20. The solid was calcined at 600 K for 4 h to remove the copolymer. Ti in the form of titanium isopropoxide was grafted onto the dehydrated surface of SBA-15 Pore diameter = 6.3 nm, surface area = 518 m2/g, pore volume = 0.68 (25)... 

Most grafting methods initiate mainly long chains which grow out from a few active sites on the fiber substrate. It is usually difficult to influence the number and the length of the grafted chains, grown by free radical processes. 

Table 9.10 Structural characteristics of dendritic polystyrenes obtained by the self-convergent grafting method (adapted from ref. 29)...

Deleuze et al. used the same approach for the synthesis and functionalization of emulsion-derived polymeric foams [119]. Alternatively, a post-synthesis grafting method recently developed in our group offers access to high-capacity functionalized monolithic systems. Such high capacity monoliths are vital to various applications such as catalysis, extraction of environmental contaminants, extraction of biochemicals for either pharmaceutical or clinical purposes or, more generally, separation techniques [100]. With these systems, amounts of grafted monomers can exceed 1 mmol/g [94]. 

S- [51], and C- [49,52] a-sialosides have been prepared using copolymerization or grafting methods. More complex sialylohgosaccharide-containing polymers have also been prepared, including GM3 [53], sialyl Lewis [54], sialyl Lewis [55], and a related 3 -sulfo-Lewis analog [56, 57], including polymerized liposomes [58]. 

Recently this grafting methods has been used to synthesize amphiphilic graft copolymers in which hydrophilic grafts are linked to a hydrophobic backbone. Partly chloromethylated polystyrene is used to deactivate either monofunctional "living" polyethylene oxide or monofunctional "living" polyvinylpyridine. In the latter case subsequent quaternization yields polyelectrolyte grafts. ... 

Niobium and titanium incorporation in a molecular sieve can be achieved either by hydrothermal synthesis (direct synthesis) or by post-synthesis modification (secondary synthesis). The grafting method has shown promise for developing active oxidation catalyst in a simple and convenient way. Recently, the grafting of metallocene complexes onto mesoporous silica has been reported as alternate route to the synthesis of an active epoxidation catalyst [21]. Further the control of active sites, the specific removal of organic material (template or surfactant) occluded within mesoporous molecular sieves during synthesis can also be important and useful to develop an active epoxidation catalyst. Thermal method is quite often used to eliminate organic species from porous materials. However, several techniques such as supercritical fluid extraction (SFE) and plasma [22], ozone treatment [23], ion exchange [24-26] are also reported. 

The purely siliceous MCM-41 and Ti-containing MCM-41 were synthesized by the solvent evaporation method. The chiral salens were immobilized step by step on the siliceous MCM-41 by the new grafting method using 3-aminopropyltrimethoxysilane and 2,6-diformyl-4-tert-butylphenol. The enantioselective diols could be synthesized directly from olefins using the hybrid catalysts of chiral salen complexes and Ti-MCM-41. 

For this study, the chiral salen complexes were synthesized and immobilized onto the MCM-41 by a new multi-grafting method according to the procedure as shown in Scheme 1. In addition, homogeneous symmetrical and unsymmetrical chiral salen complexes of similar structure to the immobilized ones were synthesized to compare the enantioselectivity in the reactions. 

In conclusion, the chiral salen Co(III) complexes immobilized on Si-MCM-41 colud be synthesized by multi-grafting method. The asymmetric synthesis of diols from terminal olefins was applied with success using a hybrid catalyst of Ti-MCM-41/chiral Co(III) salen complexes. The olefins are readily oxidized to racemic epoxides over Ti-MCM-41 in the presence of oxidants such as TBHP, and then these synthesized diols are generated sequentially by epoxide hydrolysis on the salen Co(lll) complexes. This catalytic system may provide a direct approach to the synthesis of enantioselective diols from olefins. 

With adequate swelling vinyl monomers can be satisfactorily grafted to cellulose and its derivatives by the three main methods developed for other polymers (98). These are (1) the mutual or direct method where the polymer is irradiated in the presence of the monomer or monomer vapor, (2) the pre-irradiation (sometimes called post-irradiation grafting) method where the polymer is first irradiated and then brought into contact with the monomer, and (3) the peroxide method in which the polymer is irradiated in air and the resulting polymeric peroxide used to initiate graft polymerization. 

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