The properties and morphologies of poly(4-vinylpyridine-co-styrene) [P(4VP/St)] lattices, prepared by soap-free emulsion polymerization using the water-soluble initiator 2,2'-azobis(2-amidinopropane) 2HCl (V50), were greatly affected by the addition of ethyl acetate (EA). The properties and morphologies of the resultant lattices were characterized by measuring the zeta potential, viscosity average molecular weight, particle size and distribution, glass-transition temperature (T-g), and photographs taken by SEM and TEM. The effects of two kinds of monomer feeding modes, that is, the batch and semicontinuous emulsion copolymerization, were also investigated. For batch emulsion copolymerization, by charging EA, the core-shell morphology resulting from the disparate reactivity ratios of the 4VP(1)St(2) copolymerization system (r(1) = 1.04, r(2) = -0.73) disappeared. Instead, first a bimodal particle size distribution, with an apparently asymmetric composition structure, and then spherical microspheres were obtained as the amount of EA charged increased from 2 to 10 wt %. The particle size increased twofold by the addition of EA. The zeta potential of particles increased from +64.4 to more than +100 mV, and viscosity average molecular weight decreased from 9.70 to 0.97 x 10(5) g/mol, as EA increased from 0 to 8 wt %. With the semicontinuous copolymerization, raspberry-like particles were obtained by charging 10 wt % EA, whereas a sandwich-like morphology was obtained without EA. The DSC curves showed one T-g for all the lattices prepared with charging EA, but two T-g's for the latex prepared without using EA, regardless of the monomer feeding modes.