Products of the radical dispersion copolymerization of methacryloyl-terminated poly(ethylene oxide) (PEO) macromonomer and styrene were separated and characterized by size exclusion chromatography (SEC), full adsorption-desorption (FAD)/SEC coupling and eluent gradient liquid adsorption chromatography (LAC). In dimethylformamide, which is a good solvent for PEO side chains but a poor solvent for polystyrene (PS), amphiphilic PS-graft-PEO copolymers formed aggregates, which were very stable at room temperature even upon substantial dilution. The aggregates disappeared at high temperature or in tetrahydrofuran (THF), which is a good solvent for both homopolymers and for PS-graft-PEO. FAD/SEC procedure allowed separation of homo-PS from graft-copolymer and determination of both its amount and molar mass. Effective molar mass of graft-copolymer was estimated directly from the SEC calibration curve determined with PS standards. Presence of larger amount of the homo-PS in the final graft-copolymer products was also confirmed with LAC measurements. The results indicate that there are at least two or maybe three polymerization loci; namely the continuous phase, the particle surface layer and the particle core. The graft copolymers are produced mainly in the continuous phase while PS or copolymer rich in styrene units is formed mostly in the core of monomer-swollen particles.