Cellulose substituent distribution

Recently, use of LiCl/DMAc and LiCl/l,3-dimethyl-2-imidazolidinone as solvent systems for acetylation of cellulose by acetic anhydride/pyridine has been compared. A DS of 1.4 was obtained the substituent distribution in the products synthesized in both solvents was found to be the same, with reactivity order Ce > C2 > C3. Therefore, the latter solvent system does not appear to be better than the much less expensive LiCl/DMAc, at least for this reaction. It appears, however, to be especially efficient for etherification reactions [178]. It is possible, however, that the effect of cellulose aggregation is more important for its reaction with the (less reactive) halides than with acid anhydrides this being the reason for the better performance of the latter solvent system in ether formation, since it is more efficient in cellulose dissolution. 

The application of fluorescence labels in combination with GPC can be considered a step forward in the analysis of oxidized functionalities in cellulosics. However, a large number of questions still remain to be addressed in the future. If oxidized functionalities are considered as substituents along the polymer chain of cellulose, then a thorough analysis of the substituent distribution within the cellulose chains and per anhydroglucose unit should provide many new insights. The differentiation of aldehyde and keto functions will be a next step. Also the exact position of carbonyls (keto or aldehyde) within the AGU needs to be resolved, and differences in their reactivity determined. Furthermore, it is an open question whether oxidation occurs statistically within cellulose chains or forms clusters of highly oxidized areas. 

While SEC aims to separate a polymeric mixture only with respect to size (hydro-dynamic volume), investigations of substituent distribution requires a separation with respect to the chemistry of the constituents. Spurlin, very early on, recognized this problem and fiactionated cellulose nitrate by repeated dissolution and precipita-tion. The fractions obtained showed increasing viscosities and, related to this, increasing flexibihty of solution-cast thin films. Saake et al. also made use of this common principle in polysaccharide isolation, in particular the (stepwise in this instance) precipitation of CMC by ethanol from aqueous solution. ... 

S. Richardson and L. Gorton, Characterisation of the substituent distribution in starch and cellulose derivatives. Anal. Chim. Acta, 497 (2003) 27-65. 

W. Wagenknecht, I. Nehls, A. Stein, D. Klemm, and B. Philipp, Synthesis and substituent distribution of sodium cellulose sulfates via trimethylsilyl cellulose as intermediate, Acta Polym., 43 (1992) 266-269. 

P. W. Arisz, H. T. T. Thai, and J. J. Boon, Changes in substituent distribution patterns during the eonversion of cellulose to 0-(2-hydroxyethyl)celluloses,... 

R. Adden, R. Muller, and P. Mischnick, Analysis of the substituent distribution in the glueosyl units and along the polymer chain of hydroxypropylmethylcel-luloscs and statistical evaluation. Cellulose, 13 (2006) 459—476. 

Y. Tezuka and Y. Tsuchiya, Determination of substituent distribution in cellulose acetate by means of a C NMR study on its propanoated derivative, Carbohydr. Res., 273 (1995) 83-91. 

Y. Tezuka, K. hnai, M. Oshima, and T. Chiba, Determination of substituent distribution in cellulose ethers by means of a carbon-13 NMR study on their acetylated derivatives. 1. Methylcellulose, Macromolecules, 20 (1987) 2413-2418. 

S.-J. Lee, C. Altaner, J. Puls, and B. Saake, Determination of the substituent distribution along cellulose acetate chains as revealed by enzymatic and chemical methods, Carbohydr. Polym., 54 (2003) 353-362. 

B. Saake, S. Lebioda, and J. Puls, Analysis of the substituent distribution along the chain of water-soluble methyl cellulose by combination of enzymatic and chemical methods, Holzforschung, 58 (2004) 97-104. 

Other characteristics of cellulose derivatives that influence its properties are molecular weight (MW), MW distribution, and substituent distribution in and over the polymer chains. ... 

Esters of cellulose with interesting properties such as bioactivity and thermal and dissolution behavior can be obtained by esterification of cellulose with nitric acid in the presence of sulfuric acid, phosphoric acid, or acetic acid. Commercially important cellulose esters are cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate. Cellulose esters of aliphatic, aromatic, bulky, and functionalized carboxylic acids can be synthesized through the activation of free acids in situ with tosyl chloride, iV,iV -carbonyldiimidazole, and iminium chloride under homogeneous acylation with DMA/LiCl or DMSO/TBAF. A wide range of cellulose esters that vary in their DS, various substituent distributions, and several desirable properties can be obtained through these reactions. Recently, a number of enzymes that degrade cellulose esters have been reported. Some of them are acetyl esterases, carbohydrate esterase (CE) family 1, and esterases of the CE 5 [169-172] family. 

C. Altaner, J. Puls, B. Saake, Enzyme aided analysis of the substituent distribution along the chain of cellulose acetates regioselectively modified by the action of an Aspergillus niger acetylesterase, Cellulose 10 (4) (2003) 391-395. 

SCH Schagerlof, H., Johansson, M., Richardson, S., Brinkmalm, G., Wittgren, B., and Tjemeld, F., Substituent distribution and clouding behavior of hydroxypropyl methyl cellulose analyzed using enzymatic degradation. Biomacromolecules, 1, 3474, 2006. 

Tsunashima Y., Hattori K., Substituent distribution in cellulose acetates Its control and the effect on structure formation in solution, J. ColloidInterf. Sci., 228, 2000, 279-286. 

Schagerlof, H., Johansson, M., Richardson, S., Brinkmalm, G., Wittgren, B., and Tjemeld, F., Substituent distribution and clouding behavior of hydroxypropyl methyl cellulose analyzed using enzymatic degradation. Biomacromolecules, 7, 3474, 2006. Shartna, S.C., Acharya, D.P., Garcia-Roman, M., Itatni, Y., and Kunieda, H., Phase behavior and surface tensions of amphiphilic fluorinated random copolymer aqueous solutions, Colloids Surfaces A, 280, 140, 2006. 

Nakayama E, Azuma J (1998) Substituent distribution of cyanoethyl cellulose. Cellulose 5 175-185... 

The main polymers used as thickeners are modified celluloses and poly(acrylic acid). Several different modified celluloses are available, including methyl-, hydroxypropyl methyl-, and sodium carboxymethyl-cellulose and their properties vary according to the number and distribution of the substituents and according to relative molar mass of the parent cellulose. Hence a range of materials is available, some of which dissolve more readily than others, and which provide a wide spread of possible solution viscosities. Poly(acrylic acid) is also used as a thickener, and is also available in a range of relative molar masses which give rise to give solutions of different viscosities. 

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