Eluent gel permeation chromatography: Application to the association of block copolymer F127 in aqueous solution

A new method is described for the study of micellar solutions of block copolymers by gel permeation chromatography. Results are presented for the micellization in aqueous media of a poly(oxyethylene/oxypropylene/oxyethylene) triblock copolymer (Synperonic F127) which has been well studied by other methods. The new approach circumvents the dilution effect which normally greatly restricts the study of associating systems by GPC. The characteristic feature of eluent GPC is the use of the block copolymer solution as the eluent instead of simply the pure solvent. The association behaviour of the eluent at a particular concentration and temperature is probed by injecting an additional small volume of copolymer solution into the system. Studies showed that changes in concentration of the injected probe solution, within certain limits, did not affect the relative areas of the micelle and molecule (unassociated chain) peaks. The relative areas of the peaks were essentially determined by the association equilibrium within the eluent solution and provided a direct measure of the relative weight concentrations of the micelle and molecule peaks in the eluent. An analysis of elution volumes indicated there was an increase in micellar size with increasing temperature up to 20 K above the cmT.