Abstract: Based on monomer reactivity ratios and monomer partition coefficient, the glass transition temperature (T_g) of emulsion eopolymers of butyl acrylate (BA) and vinyl acetate (VA) was simulated using Johnson's equation, and T8 diagrams versus polymer weight fraction distribution was given.The simulation results, as well as experiments, showed that one T_g was observed for semi-continuous eopolymers, and two well separated T_g's for batch process eopolymers.In semi-continuous eopolymers, T_g's values constantly increase with VAcontent in the eopolymers, and by theoretical simulation of T_g's in batch eopolymers at different conversions, it is shown that the experimentally observed lower T_g, which is moving towards higher temperature zone with VAcontent in copolymerization, represents a BA-rich copolymer mainly formed in an early stage of the copolymerization, while the higher T_g, representing a nearly PVAhomopolymer and unaffected by monomer ratio variation in copolymerization, is mainly produced at a later stage of the copolymerization after BAexhausted.The theoretical simulation agrees well with experimental results.

Key words: Butyl acrylate, Vinyl acetate, Emulsion copolymerization, T_g, Theoretical simulation