Dimethylacetamide-lithium chloride

Several derivatives of cellulose, including cellulose acetate, can be prepared in solution in dimethylacetamide—lithium chloride (65). Reportedly, this combination does not react with the hydroxy groups, thus leaving them free for esterification or etherification reactions. In another homogeneous-solution method, cellulose is treated with dinitrogen tetroxide in DMF to form the soluble cellulose nitrite ester this is then ester-interchanged with acetic anhydride (66). With pyridine as the catalyst, this method yields cellulose acetate with DS < 2.0. 

In another oudine, cellulose was complexed with cuprammonium ions (Nicoll and Conaway, 1943). Lately, laboratory-scale isolation has relied on polar aprotic solvents and solvent systems, e.g., dimethylsulfoxide, pyridine, Af,7V-dimethylacetamide-lithium chloride, and l-methyl-2-pyrrolidinone-lithium chloride (Baker et al., 1978 McCormick and Shen, 1982 Seymour et al., 1982 Arnold et al., 1994). These solvents have enabled such homogeneous17 reactions as O- and N-derivatization of cellulose and chitin (Williamson and McCormick, 1994) and selective site chlorination (Ball et al., 1994). Dimethylsulfoxide was the solvent in a homogeneous reaction of cellulose and paraformaldehyde, prior to isolation of purified cellulose (Johnson et al., 1975). In yet another outline, paraformaldehyde enabled superior quality extracts when the parent tissues were presoaked in this solution (Fasihuddin et al., 1988). 

For a specific polymer, critical concentrations and temperatures depend on the solvent. In Fig. 15.42b the concentration condition has already been illustrated on the basis of solution viscosity. Much work has been reported on PpPTA in sulphuric acid and of PpPBA in dimethylacetamide/lithium chloride. Besides, Boerstoel (1998), Boerstoel et al. (2001) and Northolt et al. (2001) studied liquid crystalline solutions of cellulose in phosphoric acid. In Fig. 16.27 a simple example of the phase behaviour of PpPTA in sulphuric acid (see also Chap. 19) is shown (Dobb, 1985). In this figure it is indicated that a direct transition from mesophase to isotropic liquid may exist. This is not necessarily true, however, as it has been found that in some solutions the nematic mesophase and isotropic phase coexist in equilibrium (Collyer, 1996). Such behaviour was found by Aharoni (1980) for a 50/50 copolymer of //-hexyl and n-propylisocyanate in toluene and shown in Fig. 16.28. Clearing temperatures for PpPTA (Twaron or Kevlar , PIPD (or M5), PABI and cellulose in their respective solvents are illustrated in Fig. 16.29. The rigidity of the polymer chains increases in the order of cellulose, PpPTA, PIPD. The very rigid PIPD has a LC phase already at very low concentrations. Even cellulose, which, in principle, is able to freely rotate around the ether bond, forms a LC phase at relatively low concentrations. 

FIG. 16.30 (left) Variation of the viscosity of PpBA in dimethylacetamide/lithium chloride solutions with polymer concentration for various molecular weights expressed as intrinsic viscosities (in mVkg) ... 

Aqueous salt solutions such as saturated zinc chloride or calcium thiocyanate can dissolve limited amounts of cellulose [131]. Two nonaqueous salt solutions with a lengthy history are ammonium thiocyanate/ammonia and dimethylacetamide/lithium chloride (DMAc/LiCl). Solutions up to about 15% can be prepared with these solvents. DMAc-LiCl has been used for molecular weight determinations of cotton [135] (see Section 1.5.2). 

Conio, G. Corazza, P. Bianchi, E. Tealdi, A. Ciferri, A. Phase equilibria of cellulose in N,N-dimethylacetamide/lithium chloride solutions. J. Polym. Sci. Polym. Lett. 1984, 22 (5), 273-277. 

In this regard, polyvinyl alcohol (PVA), a hydrolysis product of polyvinyl acetate, is well suited for blending with natural polymers since it is highly polar and water-soluble synthetic polymer which is also biodegra ble. PVA and starch films have been prepared for use as agricultural mulch films and as water-soluble laundry bags. Cast films made firom PVA and cellulose, prepared in N,N-dimethylacetamide-lithium chloride, exhibited good miscibility due to their mutual ability to form infra-... 

Essentially we find in the literature just two polymers which have been spun to such fibres. Their preparation is simplicity itself merely requiring the bringing together of 2,5-dimethyl piperazine (XIV) and a bis-isocyanate of the type (XV) (where R = H or CH3) in a suitable solvent such as dimethylacetamide-lithium chloride. The resulting viscous polymer solution may be employed as the spinning dope. 

Poirier, M. and Charlet, G. (2002) Chitin fractionation and characterization in N, N-dimethylacetamide/ lithium chloride solvent system. Carbohydrate Polymers, 50, 363-370. 

Poly(e-caproamide) A, A -dimethylacetamide/lithium chloride and water 2004FEN... 

FEN FenTso, L.A., Bil dyukevich, A.V., and Soldatov, V.S., Phase diagrams of a poly(e-caproamide)-dimethylacetamide-lithium chloride system (Russ.), Vysokomol. Soedin., Ser. A, 46, 706, 2004. 

Nishio, Y. and John Manley, R.S. 1988. Cellulose-polyfvinyl alcohol) blends prepared from solutions inIVdV-dimethylacetamide-lithium chloride. Macromolecules 21 1270-1277. 

Cellulose Sulfonates. Cellulose sulfonates are inorganic esters of cellulose and sulfonic acids in which there is a sulfur-oxygen bond formed to link the cellulose and sulfonic acid moieties. Figure 4 depicts the three most common cellulose sulfonates described in the literature, cellulose methanesulfonate (mesylate) (4), cellulose toluenesulfonate (tosylate) (5), and cellulose dansylate (6) (22-25). Cellulose tosylate is the most commonly described cellulose sulfonate in the literature. Cellulose sulfonates are typically prepared in a homogeneous process by dissolving cellulose in a dimethylacetamide/lithium chloride (DMAc/LiCl) mixture and reacting the cellulose with sulfonylchloride in the presence of triethylamine (Fig. 5) (25). Cellulose sulfonates can also be prepared in situ for use as reactive intermediates (26,27). The use of cellulose tosylate as a reactive intermediate is be discussed in more detail later in this report. 

Salaris, F., Valenti, B., Costa, G. Ciferri, A. (1976). Phase equilibria of poly(p-benzamide) in N,N-dimethylacetamide/lithium chloride solutions. Makromol. Chem., Vol. 177, pp. 3073- 3076. 

Still due to the strong cohesion of this material, cellulose is insoluble in most organic solvents. Only some highly polar mixtures such as A, A -dimethylacetamide/ lithium chloride, AT-methylmorpholine/water, Cu(OH)2/ammonia, trifiuoroacetic acid/alkyl chloride, calcium thiocyanate/water, and ammonium thiocyanate/liquid ammonia are solvents of cellulose. In spite of the potential applications of such solutions, they are exploited relatively little due to their high cost. 

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