AGGREGATION BEHAVIOR OF AN AMPHIPHILIC GRAFT COPOLYMER IN AQUEOUS-MEDIUM STUDIED BY ASYMMETRICAL FLOW FIELD-FLOW FRACTIONATION

Flow field-flow fractionation (FlFFF) was used to characterize the agg regation of a charged, amphiphilic copolymer, MMA 550, prepared from p oly(styrene-co-methyl methacrylate-co-maleic anhydride) and poly(ethyl ene oxide) monomethyl ether. MMA 550 has a charged hydrophobic backbon e and hydrophilic grafts which give the polymer a complex behavior in aqueous solution. FlFFF turned out to be a powerful tool for separatio n and size determination of different polymer aggregate populations in various media. The hydrodynamic diameter of the polymer was obtained from FlFFF measurements in water and pH-adjusted solutions. In pure wa ter, the majority of the polymer molecules had a hydrodynamic diameter of 3-4 nm, which was also found at higher pH values (pH 9), When the pH was lowered, the hydrodynamic diameter increased rapidly. This sugg ested the formation of large micelles, probably polymolecular, as an e ffect of the reduced charge repulsion.