A process for the purification or fractionation of aqueous soluble
polymers using an aqueous two-phase system is described. The
concentrations of the polymer to be fractionated and of an aqueous
soluble salt, and the temperature of the aqueous fractionation medium are
adjusted so that two phases form, the lower molecular weight polymer
molecules partition into the high salt concentration phase, and the
higher molecular weight polymer molecules partition into the low salt
concentration phase. The resulting high molecular weight polymers are
characterized by a higher average molecular weight and a narrower
molecular weight distribution and decreased unsaturation than the
unfractionated polymers. After being subjected to the fractionation
process, polyol polymers that form hydrogels in aqueous solution
exhibited higher viscosities and a liquid to gel transition over a
narrower temperature range than the unfractionated polyol polymers.
