Derivatizing solvents

The basic requirement for cellulose dissolution is that the solvent is capable of interacting with the hydroxyl groups of the AGU, so as to eliminate, at least partially, the strong inter-molecular hydrogen-bonding between the polymer chains. There are two basic schemes for cellulose dissolution (i) Where it results from physical interactions between cellulose and the solvent (ii) where it is achieved via a chemical reaction, leading to covalent bond formation derivatizing solvents . Both routes are addressed in details below. 

Derivatized solvents are modified solvent molecules that are designed to mimic the solubility properties of the original solvent while greatly reducing its volatility. An example is n-octyl tetrahydrofurfuryl ether, used as a replacement for tetrahydrofuran (THF). By taking this concept a step further, immobilized solvents are solvent molecules that are tethered to a low-molecular-weight polymer, further reducing its volatility (Sherman et al., 1998). 

Immobilized and derivatized solvents are expensive to produce. The life-cycle impact of using them has not been characterized. The recyclability of the solvents has not been characterized. Separations may be difficult in some cases. 

These alkylating derivatization reactions can be accomplished within 15 min at a temperature of 353 K using acetonitrile (250,251) or dimethylformamide (245-248) as derivatization solvents. The average yield under such conditions is often higher than 97%. Although the presence of small amounts of water does not influence the reaction yield significantly (238), removal of excess water can... 

Basic studies on diazonium-CNT chemistry led to two very efficient techniques for SWCNT derivatization solvent-free functionalization [176] and functionalization of individual (unbundled) nanotubes [175], With the solvent-free functionalization (Scheme 1.26), heavily functionalized and soluble material is obtained and the nanotubes disperse in polymer more efficiently than pristine SWCNTs [176], With the second method, aryldiazonium salts react efficiently with the individual (unbundled) HiPCO produced and sodium dodecyl sulfate (SDS)-coated SWCNTs in water. The resulting functionalized tubes (one addend in nine tube carbons) remained unbundled throughout their entire lengths and were incapable of reroping. [175],... 

Fig. 6.10. Isocratic electrochromatography of an oligosaccharide ladder in a capillary filled with a macroporous polyacrylamide/poly(ethylene glycol) matrix, derivatized with C4 ligands (15%) and containing vinylsulfonic acid (10%) (Reprinted with permission from [35]. Copyright 1997 American Chemical Society). Conditions capillary length, 50 cm (40 cm effective length) x 100 pm i.d. mobile phase, 0.1% aqueous acetic acid containing 5% (v/v) acetonitrile field strength, 600 V/cm, injection, 100 V/cm for 5 s sample concentration, 30 mg/mL in derivatization solvent and thereafter diluted 1 100 in the mobile phase.

Complexatlon principle of cellulose with derivatizing solvent molecules illustrated for the case of cuprammonium hydroxide. Solvent molecules replace the existing hydrogen bonds with solvating Cu-complexes. (After Burchardt et al. [47])... 

The oldest and most widely practiced cellulose regeneration technology of the derivatizing solvent-type is the viscose rayon process. It is based, in part, on the discovery in 1857 by Cross, Bevin, and Beadle of the dissolution of sulfidized cellulose in alkali. Viscose fibers are by far the most important cellulose regenerates, amounting to an annual fiber production of 2.5 X 10 t worldwide [13,74]. 

Further processing, for example, dilution, derivatization, solvent exchange measurement... 

From the synthetic point of view, more flexibility is achieved by employing non-aqueous non-derivatizing solvents. Extensive work has been carried out on binary or ternary mixtures like inorganic or organic electrolytes in strongly dipolar aprotic solvents. The best known example is LiCl in DMA, in A-methyl-2-pyrrolidone (NMP), or in 1,3-dimethyl-2-imidazolidinone (DMI) [5]. The structure of these ceUulose/solvent system complexes has been described by several authors, differing essentially in the role played by the Li and CD ions, as comprehensively discussed in a specific review [6]. 

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