In the absence of emulsifier, we prepared stable emulsifter-free polymethylmethacrylate/polystyrene (PMMA/PSt) copolymer latex by batch method with comonomer NN-dimethyl, N-butyl, N-methacryloloxylethyl ammonium bromide (DBMEA) by using AIBN as initiator. The size distribution of the latex particles was very narrow and the copolymer particles were spherical and very uniform. Under the same recipe and polymerization conditions, PMMA/PSt and PSt/PMMA composite polymer particle latices were prepared by a semicontinuous emulsifier-free seeded emulsion polymerization method. The sizes and size distributions of composite latex particles were determined both by quasi-elastic light scattering and transmission electron microscopy (TEM). The effects of feeding manner and staining agents on the morphologies of the composite particles were studied. The results were as follows: the latex particles were dyed with pH 2.0 phosphotungestic acid solution and with uranyl acetate solution, respectively, revealing that the morphologies of the composite latex particles were obviously core-shell structures. The core-shell polymer structure of PMMA/PSt was also studied by H-1, C-13, D-2 NMR, and distortionless enhancement by polarization transfer, or DEPT, spectroscopy. Results showed that PMMA/PSt polymers are composed of PSt homopolymer, PMMA homopolymer, and PMMA-g-PSt graft copolymers; results by NMR are consistent with TEM results. (c) 2005 Wiley Periodicals, Inc.