Morphology and electrokinetic behavior of styrene-2-ethylhexyl acrylate copolymer latex for coatings prepared by two-stage seeded emulsion polymerization

Abstract

Department of Chemical Engineering, Qingdao University of Science and Technology, Qingdao, 266042, P. R. China E-mail: [email protected] Fax : 86-0532-4863434 Manuscript received 5 September 2003, revised 1 April 2004, accepted 23 August 2004 The styrene (ST)-2-methylhexyl acrylate (EHA) copolymer latexes were synthesized through two-stage seeded emulsion polymerization (TSSEP) technique which were compared with the conventional emulsion polymerization (CEP) technique. The morphologies, particle size and electrokinetic behaviors of TSSEP and CEP latexes were studied through transmission electron microscopy (TEM) and Zetasizer respectively. It was found that the latex particles of TSSEP were all uniform and almost spherical in morphology. The particle size as well as polydispersity of TSSEP latex was smaller than that of CEP latex, and the particle size measurement of TEM corresponded with that of Zetasizer. Electrokinetic studies showed that all latexes were negative systems, and the particles exhibited colloidal stability under basic conditions. The negative value of ζ-potential for TSSEP latex was larger than that for CEP latex over the whole range of measured pH and NaCI concentrations, i.e. TSSEP latex demonstrated higher electrostatic stability than CEP latex. The ζ-potential reached the maximum value at approximately 3 x 10^-3 mol dm^-3 of NaCI concentration indicating the highest colloidal stability of TSSEP and CEP latexes. At very high salt concentration ([NaCi] = 0.1 M), we obtained very small ζ-potential values, thus the colloidal stability of ST-EHA copolymer latexes was much low.