Grafting direct

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 ... 

Radical induced grafting may be carried out in solution, in the melt phase,292 29 or as a solid state process.296 This section will focus on melt phase grafting to polyolefin substrates but many of the considerations are generic. The direct grafting of monomers onto polymers, in particular polyolefins, in the melt phase by reactive extrusion has been widely studied. Most recently, the subject has been reviewed by Moad1 9 and by Russell.292 More details on reactive extrusion as a technique can be found in volumes edited by Xanthos," A1 Malaika and Baker et a 21 7 The process most often involves combining a frcc-radical initiator (most commonly a peroxide) and a monomer or macromonomer with the polyolefin as they are conveyed through the extruder. Monomers commonly used in this context include MAII (Section 7.6.4.1), maleimidc derivatives and malcate esters (Section 7.6.4.2), (meth)acrylic acid and (meth)acrylate esters (Section 7.6.43), S, AMS and derivatives (Section 7.6.4.4), vinylsilancs (Section 7.6.4.5) and vinyl oxazolines (Section 7.6.4.6). 

The rhodium complex with bis(diphenylphosphino)phenoxazine was immobilized on silica using the sol-gel technique or by a direct grafting to commercially available silica [127]. Under standard hydroformylation conditions (CO/H2 atmosphere), a neutral hydridic complex (57) and cationic species (58) (Scheme 4.35) coexist on the support and act as a hydroformylation/hydrogenation sequence catalyst, giving selectively 1-nonanol from 1-octene 98% of 1-octene were converted to mainly linear nonanal which was subsequently hydrogenated to 1-nonanol. The... 

Three predominant routes have been developed for the solution-grafting of organorare-earth metal /actinide complexes (i) direct grafting (route A),... 

Scheme 12.8 (a) Introduction of bulky ligands (L ) by direct grafting of heteroleptic lanthanide silylamide complexes on mesoporous MCM-41 (22-25) (cf route A in Scheme 12.3) (b) grafting of (homoleptic) lanthanide silylamide complexes on a mesoporous material (cf route A in Scheme 12.3) followed by a subsequent ligand exchange (cf route C in Scheme 12.3) via protonolysis of the Ln-N bond with HL (A-L). 

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 2 Direct grafting of dioxomolybdenum complexes Mo02X2(THF)2 onto MCM-41 and MCM-48...

Schemes Direct grafting of CpMo(CO)3Cl onto zeolites containing alumina (zeolite- 8, zeolite-Y, AM-41, AM-48) and zeolites not containing aliunina (SM-41, SM-48)...

In liquid phase, by direct grafting, much work has been done especially using cobalt-60 source of irradiation. 

A review on individual monomers using gamma-rays irradiation, still by direct grafting of polyamides, is presented below. 

In the vapor phase, by direct grafting, a large number of authors have studied gamma-rays as the agent for creating active centers in the polyamidic backbone at room temperature. Dose irradiation ranges usuafly from 0.5 to 19Mrads. 

The literature reports direct grafting by gamma-rays exposure of Nylon fibers or films to the following monomers carbon monoxide (/65), ethylene (157), propylene (157), acetylene (166), butadiene (157.162,163), styrene (158, 161,163,167,168), vinyl chloride (157,163), vinyl fluoride (169-172), vinyl acetate (161,163,173), vinyl propionate (161), vinyl butyrate (161), vinyl crotonate (161), vinyl 2-ethyl hexanoate (161), acrylic add (173,174), methyl acrylate (162, 163), ethyl acrylate (162,163), allyl acrylate (163), methyl methacrylate (28,161, 163,164), butyl methacrylate (161), acrylamide (158), methylol acrylamide (163), acrylonitrile (157,160-163, 167, 175-179), divinyl sulfone (161), vinyl pyridine (167,173), vinyl pyrrolidone (28) and triallyl cyanurate (158). 

Heating the monomer vapors to which Nylon pellets, fibers or films are exposed, is another method for direct grafting, although not much used. Ethylene oxide vapors at about 80° C have been successfully employed for graft copolymerization of the polyamide skeleton by that procedure (187,188). 

In the present work the synthesis of highly dispersed niobium or titanium containing mesoporous molecular sieves catalyst by direct grafting of different niobium and titanium compounds is reported. Grafting is achieved by anchoring the desired compounds on the surface hydroxyl groups located on the inner and outer surface of siliceous MCM-41 and MCM-48 mesoporous molecular sieves. Catalytic activity was evaluated in the liquid phase epoxidation of a-pinene with hydrogen peroxide as oxidant and the results are compared with widely studied titanium silicalites. The emphasis is directed mainly on catalytic applications of niobium or titanium anchored material to add a more detailed view on their structural physicochemical properties. 

In agreement with catalytic results it is clear that upon direct grafting, a very high dispersion of isolated tetrahedral centres may be generated on the walls of mesoporous MCM-41 and MCM-48. This in turn allows for the possible tuning to improve the catalytic activity while preserving the mesoporous framework intact. Epoxidation with samples where template was removed by solvent extraction proceeds at better rate than with other mesoporous samples. 

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