Grafting, anionic Process polymers

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 methods for obtaining polymer chains grafted onto the surface of nanoparticles can be divided into two classes grafting-from and grafting-to processes. In the former method, the nanoparticle surface is modified with functional groups by the reaction between molecules and particles, and then the molecules begin the polymerization processes via radical, cationic, or anionic polymerization. In the latter method, the groups at the end of preformed polymers react with the nanoparticle surface. 

This polymerization technique provides an extensive and unprecedented control over the polymerization process. This includes polymer composition, microstructure, molecular weight, molecular weight distribution, choice of functional end groups and even monomer sequence distribution. The synthesis of graft copolymers by anionic pol3nnerization can be achieved either by "grafting from" or by "grafting onto" processes. 

Grafting onto" processes require reacting the anionic sites of a "living" polymer with electrophilic sites fitted on the backbone of another macromolecule. ... 

The second approach for improving the processabihty of ICPs is to prepare their colloidal dispersions in water or an appropriate solvent The colloid dispersions of ICPs can be obtained by chemical or electrochemical oxidation of the monomer in the presence of a steric stabihzer [29-31].The key parameter for such synthesis is the choice of an appropriate steric stabihzer which adsorbs or grafts onto the polymer coUoidal particles to prevent their aggregation or precipitation. Several polymers such as polyfethylene oxide) [32], poly(vinyl pyrroHdone) [33,34], poly(vinyl alcohol) [35], ethyl hydroxy cellulose [36], poly(vinyl alcohol-co-acetate) [37], poly(vinyl methyl ether) [38,39] and block copolymer stabihzer [40] have been used as steric stabihzers to produce PPy coUoidal dispersions. Surfactants are also employed for the synthesis of ICP coUoidal dispersions [41,42]. Very recently, stable PPy dispersions were prepared by Lu et al. by polymerizing pyrrole in an aqueous medium containing different anionic salts such as sodium benzoate, potassium hydrogen phthalate, and sodium succinate [43]. These authors also reported that the conductivity of PPy dispersions was enhanced when sodium benzoate was used as dopant. Chemical oxidahve polymerization in the presence of PSS in aqueous medium produces coUoidal dispersions and improves processability [44]. CoUoidal dispersions... 

The living anionic ends can be functionalized by adding such agents as ethylene oxide, carbon dioxide, and methacryloyl chloride [33]. The resulting new polymer is capable of being copolymerized with additional monomers. This process can lead to the formation of various graft copolymers [29-32]. 

The emulsion polymerization process involves the polymerization of liquid monomers that are dispersed in an aqueous surfactant micelle-containing solution. The monomers are solubilized in the surfactant micelles. A water-soluble initiator catalyst, such as sodium persulfate, is added to the aqueous phase. The free radicals generated cause the dispersed monomers to react to produce polymer molecules within the micellar environment. The surfactant plays an additional role in stabilizing dispersion of the produced polymer particles. Thus, the surfactants used both provide micelles to house the monomers and macroradicals, and also stabilize the produced polymer particles [193,790], Anionic surfactants, such as dodecylbenzene sulfonates, are commonly used to provide electrostatic stabilization [193], These tend to cause production of polymer particles having diameters of about 0.1-0.3 pm, whereas when steric stabilization is provided by, for example, graft copolymers, then diameters of about 0.1-10 pm tend to be produced [790,791]. 

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