Grafting, anionic Chemical methods

In another elegant application of the masked disilene method, the anionic polysilanyl chain ends were chemically bound to substrate surfaces to form end-graft polysilanes. These systems are discussed in Section 3.11.4.2.3. 

The production of aldehyde groups through periodate oxidation and subsequent formation of oxime groups is being used as a basis for an anionic initiation of grafting with titanium chloride as catalyst according to a process claimed by Asahi Chemical Industries Company (135). With this method styrene was grafted onto viscose rayon. Also bi- and tri-valent vanadium salts can be used as initiators. 

Grafted Types. Graft polymers have been synthesized by a variety of approaches including all of those mentioned earlier (anionic, cationic, radical, etc.). Four of these approaches will be described in this chapter. However, the reader should recognize that many chemical paths to grafting are available, albeit many of these suffer from the complexity of products produced and overall inefficiency of the grafting method. 

Similar to PANI, the carbon-related materials, activated carbon, carbon nanotube, and GO, were also doped with PPy to fabricate PPy/carbon-related material composites for wastewater treatment. PPy/impregnated porous carbon was prepared by vapor infiltration polymerization technique to obtain a mesoporous structure [72], The as-prepared composite exhibited an improved adsorption ability to remove heavy metal ions, such as Hg(II), Pb(II), and Ag(I) due to amino groups of PPy. PPy/carbon nanotube composites can be prepared by grafting from technique either chemically or electrochemically. The chemical fabricated PPy/carbon nanotube composite can effectively remove heavy metals, anions and chemical oxygen demand from paper mill waste [73]. The electrochemical synthesized PPy/carbon nanotube provided a simple and highly effective method for ClO removal via electrically switched ion exchange technique (Figure 11.15) [74]. 

The grafting onto, although offering unlimited chance for various architeaures, suffers from stria reaction conditions, which are almost similar to those used in the anionic polymerization process. The highly aaive polymer anion has less tolerance to functional groups for further chemical reaaion or modification. Click chemistry may overcome this shortcoming, but there is still no efficient method to attach long side chains to the backbone. 

The grafting-to method (without involving elaborate synthetic procedures) involves a chemical reaction between (end)-functionalized polymers and complementary reactive groups on the surface of nanoparticles. The reactive polymers can be synthesized by controlled radical, anionic, or other polymerization techniques. Compared with other polymer attachment techniques, the (end)-functionalized polymer can be thoroughly characterized via various chemical and physical methods. However, the major shortcoming of this method is the low maximum thickness of the obtained polymer layers [113]. 

Some efforts have also been directed towards the preparation of anion exchange membranes from polymer films (approach b ). Generally, these polymers, e.g., polymer films of hydrocarbon polyethylene and polypropylene or fluorocarbon origin (ETFE, PVDF), are insoluble in solvents. The method most commonly used consists in grafting vinyl monomers, such as styrene, onto polymer films followed by subsequent chemical modifications, such as chloromethylation-amination instead of sulfona-tion [6-8]. 

Novel polyimide-g-nylon 6 and nylon 6- polyiniide-] nylon 6 copolymers were synthesized by polycondensation and subsequent anionic, ring-opening polymerization methods. The graft and triblock copolymer structures were characterized with FTIR, GPC, selective extractions, DSC,TGA, tensile test and DMA. The effective reinforcement of nylon 6 with the incorporation of only a few wt% polyimide was demonstrated by the sigmOcant improvements in the copolymers thermal and mechanical properties, and chemical resistance. 

Of all the polymerization methods, the anionic [2] and controlled radical polymerizations [3] give the best control over the chain length and produce polymers with the lowest polydispersities. In addition, polymers prepared through these routes bear a terminal function that can add to one of the double bonds (6-6 bonds) of Cgq respectively, a carbanion, a stabiUzed radical or a bond that can be converted into a radical. Furthermore, it is possible to take advantage of the specific shape and chemical reactivity of Qo to perfectly control the number of polymer chains grafted onto the fullerene using these two types of addition. This is why the mechanism of these two addition reactions will be discussed in more detail. 

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