Loske, S., Lutz Andreas, Striouk, S. and Wolf, B. A.
"Fractionation of unsubstituted cellulose from solutions in either Ni-tren or (dimethylacetamide + LiCl)"
Macromolecular Chemistry and Physics 2000, 201, 1940-1945.
Abstract: Starting from solutions of unsubstituted cellulose (Avicel PH101, Mw = 30.1 kg/mol and Mw/ Mn = 3 or Solucell 500, Mw = 230 kg/mol, Mw/ Mn = 2.8) in either Ni-tren (0.8 M aqueous solution of the dihydroxo-tris(2-aminoethly)amine-nickel(II)-complex) or in a mixed solvent DMAc+LiCl (consisting of N,N-Dimethylacetamide plus lithium chloride) it was investigated whether the segregation of a second phase caused by the addition of suitable precipitants leads to polymer fractionation. With Ni-tren the long chains accumulate in the precipitate formed upon the addition of sulfuric acid; as the pH falls below 9, the solution is free of cellulose. Nevertheless this route option for fractionation must be ruled out because of a pronounced chain scission taking place in that solvent. For (DMAc+LiCl) the best low molecular weight precipitant that could be found was acetone; it allows the fractionation of the lower molecular weight Avicel but fails for Solucell as a result of the high viscosities of its solutions in the presence of acetone. It was therefore investigated whether that deficiency could be overcome by the use of high molecular precipitants. In these experiments poly(methyl methacrylate), incompatible with cellulose, was used to cause phase separation. The results demonstrate the suitability of this system for discontinuous experiments even in the case of the higher molecular weight Solucell.
preprint number: 208