Cellulosates, alkali metal initiator

Recently, the methods of anionic graft polymerization of vinyl monomers have been adopted for graft pol3nnerization to cellulose, and a few papers have appeared in the literature.All of these involve the "grafting from" process. Alkali metal cellulosates are used as initiators for the anionic graft polymerization of vinyl monomers (Scheme 1). Although this method seems more versatile it does not allow adequate structural control, and it often yields rather polydisperse samples. 

The first attempts to produce a graft copolymer of poly(amino acids) onto the natural polymers, such as cellulose, starch, and their derivatives, were carried out by Zilka and Avny in 1965. Sodium methoxide was known to be an initiator of NCA polymerization. Therefore, they proposed to use alkoxide derivatives of polysaccharides as macroinitiators for the graft copolymerization of NCA s of a-amino acids. All known methods for production of alkoxide derivatives of natural polymers, such as the reaction of polyhydroxy polymers with sodium metal in liquid ammonia, or exchange reactions between lower alkoxides and polyhydroxy polymers, - were unsatisfactory for the subsequent graft copolymerization of NCAs, because any residual base would lead to homopolymerization. In addition, alkoxide derivatives of cellulose acetate and nitrocellulose could not be obtained by these conventional methods due to chemical degradation. Zilka et al., finally found that the reaction of alkali metal naphthalenes [20] with polyhydroxy polymers in either... 

It should also be noted that some nonradical ionic and condensation reactions of monomers with cellulose are used to modify the properties of cellulosic products. In one type of anionic-initiated reaction of monomers, cellulose is reacted with concentrated aqueous solutions of alkali metal hydroxides to yield cellulose copolymer. Free alkali metal in liquid ammonia or alkali metal alkoxides in nonaqueous systems may also be used as initiators of cellulose alkoxide derivatives. In cationic-initiated formation of copolymers, cellulose is reacted with an acid, such as boron trifluoride, to yield a cellulosic carbonium ion which initiates reactions with vinyl monomers. Condensation reactions of cyclic monomers with cellulose also form copolymers. Cellulose is usually slightly oxidized and also has reactive hydroxyl groups on carbons C-2, C-3 and C-6 of the anhydroglucose unit. The reactions of cyclic monomers are initiated at these carbonyl groups. A heating step may increase cellulosic oxidation and thereby increase the yield of these condensation products of cellulose and cyclic monomers." ... 

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