Preparation And Properties Of Emulsifier-Free St/BA Latexes In The Presence Of Functional Monomers

A series of stable and high solid content (-wt50%) St/BA emulsifier-free latexes were successfully synthesized with the addition of a small amount of functional monomers AMPS and AHPS. The influences of St/BA ratio, amount of functional monomers and initiator on the properties of the emulsifier-free latexes (such as the monomer conversion ratios, polymerization stability, particle diameter and zeta potential) and the latex films (such as glass transition temperature Tg, water resistance and solvent resistance) were studied in detailed. The character groups of emulsifier-free latexes copolymers were characterized by Fourier Transform Infrared (FTIR) Spectrometer. The size distribution and morphology of the latex particles were characterized by means of PCS and transmission electron microscopy (TEM). Latexes stability such as stability against electrolytes, freeze-thaw stability and pH stability were investigated as well.The results show that the two functional monomers have been successfully bonded onto the particle surfaces. The size of emulsifier-free latex particles is400-600nm in diameter, which is larger than that of the conventional latex particles. And the particle size distribution is narrow and uniform. The diameter of the latex particles decreases with the increasing content of styrene, initiator KPS and functional monomers AMPS and AHPS in the emulsifier-free emulsion polymerization system. And the water uptakes of the films increase with the increasing content of initiator KPS and functional monomers AMPS and AHPS in the emulsifier-free emulsion polymerization system. The water uptakes of the films prepared by emulsifier-free latex are much lower than that of the conventional latex sample. Compared with the film that prepared by conventional latex, solvent resistant of emulsifier-free latex film is greatly improved. The glass transition temperature results show that the compolymers’Tg decrease with the increasing of the contents of the monomer BA. The results also show that polymerization methods have no influence on Tg at the same St/BA ratio. The zeta potential values of the emulsifier-free latexes decrease with the increasing contents of functional monomers AMPS and AHPS. And when the contents of functional monomers are high enough, the zeta potential values will increase. The zeta potential values of the emulsifier-free latexes varied in range from-38.1mV to-49.2mV, and most of them were below the zeta potential value of the conventional latexes. The viscosity measure result shows that the apparent viscosity decreases sharply as the shear rate increases (called shear thinning). The emulsifier-free latexes belong to pseudoplastic non-Newtonian fluid. The stability results show that, the latex stabilized with functional monomers AMPS and AHPS have better stability against electrolytes and pH stability than those stabilized with SDS. And none of the emulsifier-free latex and conventional latexes can resist the freeze/thaw test.