Alkali soluble associative latex thickeners with hydrophobic multi-phenyl groups were prepared with methacrylic acid, ethyl acrylate, diallyl phthatale and varying amount of a functional monomer, triphenylethyl phenoxy polyoxyethylene ether methacrylate (SEM-25), through emulsion polymerization using a semi-batch process. Thickener latexes of different SEM-25 contents were diluted to different solids, light transmittance and viscosity variations with pH were followed. It was found that light transmittance of the thickener latex sharply increased with varied pH from 6 to 7 due to solubilization of the thickener polymer, which was followed by a plateau region once the thickener latex turned into an aqueous polymer solution. For all latex thickeners, a maximum in viscosity was observed with pH increase. It was revealed that, in order to have a high thickening performance, the solids in the latex thickeners should be kept at an adequate level, equal to or higher than 0.5 wt% regardless of their SEM-25 contents. By comparing the properties of the latex thickeners of different SEM-25, it was observed that the thickener with 1.1 wt% of SEM-25 displayed the lowest viscosity; whereas the one with 5.0 wt% of SEM-25 performed equally to that free of SEM-25; and the thickener with 12 wt% SEM-25 manifested a highest viscosity, providing that solids in the latex thickeners were kept at 0.65 wt% or higher. The experiments were then carried out with the same latex thickeners with varied shearing rate. It was seen that the latex thickener with 5.0 wt% and 12 wt% of SEM-25 outperformed SEM-25 free sample in thickening in all tested shearing range; while the one with 1.1 wt% of SEM-25 showed the lowest thickening effect among all thickener latexes at all tested shearing rates. Finally, 4 latex thickeners, with 0 wt%, 1.1 wt%, 5.0 wt% and 12 wt% of SEM-25 respectively, were separately blended into an aliquot of St-BA (styrene-butyl acrylate) latex of 30 wt% solids. Rheology of the compounded latex was tested. Results showed that the samples done with higher SEM-25 (5.0 wt% and 12 wt%) manifested higher thickening effect than those without SEM-25, and the latter also outperformed the sample done with 1.1 wt% of SEM-25. A detailed discussion on the mechanisms of SEM-25 thickening was given.

Key words: SEM-25 functional monomer, associative latex thickener, hydrophobically modified alkali-soluble latex, viscosity