Ionic grafting

Thus, confirmation of whether the product obtained in an attempted reaction in a true random copolymer is important to clarify the mechanism of the propagation reaction and to correlate structure and reactivity in ring-opening polymerizations. Considering that apparent copolymers may be formed by reactions other than copdymerization, for example, by ionic grafting or by combination of polymer chains, characterization of cross-sequences appears to be one of the best ways to check the formation of random copolymers. 

Ding, J. F, Chuy, C. and Holdcroft, S. 2002. Solid polymer electrolytes based on ionic graft polymers Effect of graft chain length on nano-structured, ionic networks. Advanced Functional Materials 12 389-394. 

This chapter is concerned primarily with the simultaneous polymerization of two monomers to produce statistical and alternating copolymers. The different monomers compete with each other to add to propagating centers, which can be radical or ionic. Graft and block copolymers are not synthesized by the simultaneous and competititive polymerization of two monomers. Each monomer undergoes polymerization alone. A sequence of separate, noncompetitive polymerizations is used to incorporate the different monomers into one polymer chain. The synthesis of block and graft copolymers and variations thereof (e.g., star, comb) are described in Secs. 3-15b-4, 3-15b-5, 5-4, and 9-9. 

Of particular interest are certain ionic graft copolymerizations in which the polymerization reaction is initiated only on the macromolecular framework and no homopolymer is formed. An example is provided by the formation of polymeric carbonium ions from chloride-containing polymers, such as poly(vi-nylchloride), in the presence of diethylaluminum chloride ... 

Perhaps the most promising applications of grafted cellulose are those related to ionic grafted side chains such as polyacrylic acid. These grafts can be synthesized either by direct... 

Both methods are very general. They apply to any polymer which undergoes radiolysis (i.e., "any" polymer) and the only limitation with respect to the monomer is that it polymerize by a free radical mechanism. Ionic grafting was also initiated by radiation (28,29) but the yields of this process are generally quite low. 

Ionic grafting usually leads to well defined copolymers due to the limited (if any) termination reactions. Anionic sites can be created by metallation of the backbone. This can be accomplished by complexation of several types of C-H bonds (allylic, benzylic, aromatic) with organometallic compounds such as sec-BuLi. Usually chelating compounds, for example N,N,N/>N/-tetra methyl ethylene diamine (TMEDA), act as solvating bases facilitating the reaction. By this method PB-g-PS [36-38] and Pl-g-PS [39] graft copolymers have been prepared. 

Grafting from is useful since many polymers can he used together with a range of reaction conditions (radical and ionic). Grafting through is also convenient but requires the synthesis of a macromonomer. Grafting onto is the least useful method since reactions between polymers are slow and there are relatively limited numbers of polymers with functional... 

Another example of ionic graft copolymerization is a reaction carried out on pendant olefinic groups using Ziegler-Natta catalysts in a coordinated anionic-type polymerization. The procedure consists of two steps. In the first, diethylaluminum hydride is added across the double bonds. In the second the product is treated with a transition metal halide. This yields an active catalyst for polymerizations of a-olefms. By this method polyethylene and polypropylene can be grafted to butadiene styrene copolymers. Propylene monomer polymerization results in formations of isotactic polymeric branches ... 

Graft copolymers possessing ionic grafts bound to a hydro-phobic backbone appear suitable as struaures for studying... 

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