Hydrophobically modified alkali-soluble latex thickeners were prepared by semi-batch emulsion polymerization using methacrylic acid, ethyl acrylate, diallyl phthalate as the main monomers, with a varying amount of behenyl polyoxyethylene ether methacrylate (BEM) as functional monomer. Viscosity, light transmittance, particle size and its distribution of the thickener latexes were determined. Viscosity and light transmittance variations with pH were followed at different solids of the latexes. It was found that particle size increased with BEM content. Light transmittance of thickener latexes sharply increased when pH varied from 6.5 to 7.5, and remained relatively constant with continuing pH increase; while for the viscosity, a significant increase was also observed, this increase followed by a fast decline after a maximum. Compared with latex thickener without BEM, performance and shear resistance of the associative latex thickeners were enhanced when BEM content was below 5.0 wt% relative to total monomers mass and at 0.5 wt% solid or higher. However, performance and shear resistance of the thickeners bearing more BEM (8.0% or higher) were reduced. Thickening performance of thickeners for a latex of poly(styrene-acrylate) was investigated. Results showed that the samples done with 2.5 wt% BEM manifested highest thickening effect among all samples. Thickeners modified with BEM possessed higher thickening performance with less functional monomer than those prepared with triphenylethyl phenoxy polyoxyethylene ether methacrylate (SEM-25).

Key words: BEM functional monomer, associative latex thickener, hydrophobic modification, viscosity