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The graft copolymers (polystyrene-graft-polyoxyethylene) (PSt-graft-PEO) were prepared by the radical dispersion copolymerization of methacryloyl (MA)-terminated PEO macromonomer and styrene. By means of size-exclusion chromatography, liquid chromatography at the critical adsorption point, and light scattering, the molecular weight parameters and the solution properties of PSt-graft-PEO were investigated. The apparent average molecular weight and the molecular weight distribution (MWD) of graft copolymers were found to decrease with increasing molecular weight of PEO-MA macromonomer. This decreased molecular weight was attributed to the chain transfer to PEO unit and increased contribution of the solution polymerization. The broad MWD varied with the ratio of the polymerization in the continuous phase and the polymer particles. The number of PEO grafts per PSt backbone decreased with increasing molecular weight of the PSt-graft-PEO copolymer, which was attributed to the intramolecular association of PEO segments. The intrinsic viscosity or the coil size of graft copolymer molecules varied with temperature as a result of the dehydration of PEO segments. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3087–3097, 1999