Synthesis and characterization of self-crosslinkable zinc polyacrylate latices at room temperature

Abstract

The zinc ion self-crosslinkable polyacrylate latexes (PAs) cured at room temperature were synthesized by seeded semi-continuous emulsion polymerization with zinc oxide (ZnO) as crosslinker. The ZnO and methacrylic acid (MAA) mass contents, method of ZnO introduction in relation to the degree of crosslinking, and the properties of self-crosslinkable latices are examined and discussed. The characterization techniques such as Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA) have been used to determine the structure and properties of PAs. The experimental results show that in a certain range, the average particle size decreases with an increase in the content of MAA, while the latex stability is undoubtedly improved. The optimum mass content of MAA is 12 % of the total monomers. The optimum amount of ZnO needed is 25 % (mole fraction) of MAA, and the optimum temperature of ZnO introduction is 60 °C. TEM analyses show that the latex particles are coarse spherical particles with surface enriched with comprising abundant carboxyl groups, and zinc ions are dissociated as zinc ammine complex in the aqueous phase. FTIR analyses confirm that the chelate crosslinking occurs between zinc ions and carboxylic acid during the film-forming process. The DSC results indicate that the glass transition temperature (Tg) of PAs increases as a function of the formation of a coordinate structure, and the obtained film exhibits excellent initial hardness and sandability. TGA analyses demonstrate that the introduction of ZnO evidently enhances the thermal stability of self-crosslinkable PAs.