A study has been made of the stability and copolymerization of concentrated emulsion of styrene (St) and butyl acrylate (BA) in the presence of polyurethane macromonomer (DPUA), which contains C=C at one end. First, the DPUA macromonomer was synthesized from the appropriate amount of 2,4-diisocyanate (TDI), polypropylene glycol (PPG), 2-hydroxyethyl methylacrylate (HEMA), dimethylolpropionic acid (DMPA), and triethylamine (TEA) by four steps. Then, the DPUA was dissolved in St-BA monomer mixtures. The DPUA/St-BA concentrated emulsion copolymerization using sodium dodecyl sulfate/cetyl alcohol (SDS/CA) as composite surfactant and polyvinyl alcohol (PVA) as liquid film reinforcer, and ammonium persulfate/sodium hydrogen sulfate (APS/SHS) as redox initiator system was carried out at 30 degrees C. The effect of NCO/OH molar ratio, surfactants' concentration, mass ratio of DPUA/St-BA, initiators' concentration, volume fraction of the monomer phase (Phi), and temperature on the stability or the copolymerization of the concentrated emulsion of DPUA/St-BA were investigated. The average size and distribution of the latex particles obtained under different conditions were also analyzed. (c) 2006 Wiley Periodicals, Inc.