No abstract

Aqueous core−shell latexes were synthesized through two-step emulsion copolymerization of vinylidene chloride (VDC) with ethyl acrylate (EA) and butyl acrylate (BA), respectively. First, seed latexes of EA-VDC85 copolymers with 85% VDC content were prepared by the binary emulsion copolymerization of VDC with EA. Subsequently, EA-VDC85 seed latexes were employed in the seed emulsion copolymerization of VDC with BA and the resulting BA-VDC80 copolymers with 80% VDC content covered onto EA-VDC85 seed latexes to form the core−shell latexes. Transmission electron microscopy and dynamic light scattering characterization demonstrated that the size and size uniformity of seed latexes were influenced markedly by the content of emulsifiers in the copolymerization, and higher emulsifier content led to smaller and more uniform latexes. Furthermore, only the utilization of homogeneous seed latexes in the seed emulsion polymerization could lead the majority of the formed latexes to bear the core−shell structure. These aqueous latexes were employed as coating films for the heavy-duty anticorrosion of metal. After 500 h of harsh salt-spray corrosion, electrochemical impedance spectroscopy measurement, corrosion evaluation around the scribe and adhesion tests demonstrated that the coating films (ca. 50 μm in thickness) formed by the optimal core−shell latexes could still protect steel plates well, and the adhesions of the coating films to steel plates were still the best. After 500 h of corrosion, the coating film formed by the best seed latex still showed good barrier properties; however, it lost adhesion to the steel plate. As for the coating film formed by the BA-VDC80 shell copolymer, both its barrier property and adhesion to steel sheet became poor after 500 h of corrosion. Therefore, it could be deduced that such aqueous core−shell latexes had more excellent comprehensive anticorrosion performances than the normal latexes composed of only the core or shell copolymers, and designing a suitable core−shell structure is also a good way to promote the heavy-duty anticorrosion performances of water-borne acylate-VDC copolymer latexes.