Synthesis and aggregation behavior of amphiphilic block copolymers in aqueous solution: Di- and triblock copolymers of poly(ethylene oxide) and poly(ethyl acrylate)

Di- and triblock copolymers of ethylene oxide (EO) and ethyl acrylate (EA) were synthesized by the atom transfer radical polymerization technique. The chemical compositions of the di- and triblock copolymers as determined by NMR and gel permeation chromatography are represented by [EO(114)EA(10)] and [EA(10)EO(445)EA(10)], respectively. The aggregation behaviors of these polymers in aqueous solutions were studied using a combination of static light scattering (SLS), dynamic light scattering, steady fluorescence, time-resolved fluorescence quenching (TRFQ), and surface tension techniques. The hydrodynamic radii (R-h) of PEO-b-PEA and PEA-b-PEO-b-PEA, where PEO is poly(ethylene oxide) and PEA, poly(ethylene acrylate), in an aqueous solution possess values of 15.3 and 25.5 nm, respectively, and they are independent of the polymer concentrations, which suggest that these micelles are formed via the closed association model. The critical micelle concentration (cmc) for the di- and triblock copolymers as determined from the surface tension are 0.002 and 0.007 wt %, while the aggregation numbers (N-agg) determined from the SLS and TRFQ are 18 and 26, respectively. When the di- and triblock copolymers are mixed in various proportions, unique intermediate cmc values are obtained. The Rh of the mixtures cannot be described by the simple or inverse mixing rule, which confirms that mixed micelles are produced.