Size selective concentrating of poly(ethylene oxide) in aqueous solution by thermosensitive hydrogels

Thermally reversible hydrogels of poly(N-isopropylacrylamide-co-acrylic aci d) crosslinked with three different contents of N,N ' -methylenebis(acryl-a mide) have been swollen to equilibrium at 25 degreesC. The aqueous swelling medium comprised a 1 g (.) dm(-3) solution of two species of polyethylene oxide (PEO) the fixed species being of molecular weight (M) 0.2 kg (.) mol( -1) and the other species being of M = 1, 4, 6, 10, 35, 110 or 1700 kg (.) mol(-1). The swelling ratios (= mass hydrogel/mass xerogel) of the resultan t hydrogels were smaller than the corresponding values for swelling in pure water. The remaining solution (raffinate) was of enhanced total concentrat ion. Concentrations of each of the two polymer species in initial solution and raffinate were measured by GPC. The ability of the hydrogel to concentr ate a particular species is quantified by alpha, where alpha is the ratio o f concentrations ofthe PEO species in raffinate to that before swelling. Th ability of hydrogel to concentrate one species in preference to a differen t species is quantified by lambda, where lambda is the ratio of alpha for M = 0.2 kg (.) mol(-1) to alpha for PEO of a different M. The findings are d iscussed in part on the basis of correlation length of gel cf. equivalent h ydrodynamic radius of the PEO sample. [GRAPHICS] Values-of the size selective separation factor (lambda) for hydrogels of di fferent crosslinker content. Contents of BIS are (lozenge) 0.25 mol-%, (squ are) 0.50 mol-%, (triangle) 1 mol-%. Swelling media are aqueous solutions a t a total concentration of 1 g (.) dm(-3) of PEO-0.2 in admixture with PEO- M.