Continuous polymer fractionation: How does it function and how can it be applied to celluloses?

For basic research as well as for some technical applications it is often m andatory to have access to sufficient amounts of polymers with narrow molec ular weight distribution. In case such products cannot be synthesized they must be obtained by fractionation. A method called CPF (Continuous Polymer Fractionation) allows the separation of the starting materials in their sho rt chain and in their long chain constituents on a technical scale. This pr ocedure consists in a continuous counter-current extraction; its successive application yields products with desired molecular weights and molecular w eight distributions. So far CPF has been successfully applied to approximately two dozens of syn thetic polymers. Cellulose, however could up to now only be fractionated in its derivatized form. Hydroxyethylcellulose did not show any particular di fficulties. To prepare cellulose with narrow molecular weight distribution, CPF was also performed with trimethylsilylcellulose (where the substituent s can be easily removed); here, however it turned out necessary to overcome several problems which are particularities of the system. In order to get easier access to such products we are presently checking whether there exis t mixed solvents for cellulose which are suited for CPF.