Emulsifier-free emulsion copolymerization of styrene (St) and butyl acrylate (BA) in the presence of a cationic functional comonomer, N-dimethyl, N-butyl, Nethyl methacrylate ammonium bromine (DBMA) was carried out using azobis(isobutylamidine hydrochloride) (AIBA) as an initiator. The surface properties of particles were studied by testing the actual value of Β©N Ο© Β© Β©C and g NHΒ€ NHΒ€ on the surface of the particles and the surface charge density. The copolymer particles were characterized using transmission electron microscopy (TEM). The effects of reaction temperature, DBMA content, AIBA content, ionic strength, etc., on the conversion of the monomer and the average diameter ( D V w) and number ( Np) of copolymer particles were investigated. Under constant ionic strength, the average diameter of copolymer particles (D V w) decreased with increasing AIBA and DBMA concentrations and de- creased with increasing reaction temperature also. Moreover, it increased with increasing St content in the monomer feeding. Under a constant concentration of the comonomer and initiator as well as the constant monomer composition, D V w shows a change process of increase-decrease-increase in the ionic strength plot. The polymerization reaction rate increased with increasing the DBMA content, AIBA content, and increasing temperature. The surface charge properties of the particles were mainly decided by the DBMA content, AIBA content, ionic strength, etc. The methods of feeding the monomer affects the morphology, structure, size, and surface charge density of the particles.