Patent ID: 6218468
Filing Date: 2001-04-17
Classification: C08F,C08J

Abstract:
A process for preparing an aqueous polymer dispersion by polymerizing monomers having at least one vinyl group by the free radical aqueous emulsion polymerization method, in which an amphiphilic substance is added to the polymerization vessel before or during the polymerization or both, whereini) 1 l of water at 20.degree. C. and 1 atm is capable of taking up at least 10.sup.-4 mol of the amphiphilic substance in micellar solution;ii) the critical micelle formation concentration of the amphiphilic substance at 20.degree. C. and 1 atm in water is <10.sup.-6 mol/l; andiii) the surface tension of an aqueous or micellar solution or both of the amphiphilic substance in a molar concentration range (0<C.sub.m.ltoreq.10.sup.-4)mol/l at 20.degree. C. and 1 atm does not fall below 60 mN/m;wherein the amphiphilic substance is a two-block polymer of the formula (I) or (I'):[A].sub.a [B].sub.b (I)[B].sub.b [A].sub.a (I')wherein:[B].sub.b is a copolymer block or a homopolymer block comprising monomers selected from the group consisting of styrene, methyl styrene, chlorostyrene, vinyl esters of C.sub.1 -C.sub.8 alkanecarboxylic acids, esters of an .alpha.,.beta.-monoethylenically unsaturated carboxylic acid of 3 to 6 carbon atoms and a C.sub.1 -C.sub.8 -alkanol, butadiene and ethylene;[A].sub.a is a copolymer block or a homopolymer block comprising monomers selected from the group consisting of .alpha.,.beta.-monoethylenically unsaturated mono- and dicarboxylic acids of 3 to 6 carbon atoms, 2-acrylamido-2-methylpropanesulfonic acid, styrene sulfonic acid, vinylsulfonic acid and the alkali metal and ammonium salts of the abovementioned acids, N-vinylpyrrolidone, vinyl alcohol, ethylene glycol and propylene glycol,b is an integer which indicates the number of monomers contained in chemically bonded form in the polymer block [B].sub.b, b being .gtoreq.30, anda is an integer whose magnitude is at least 40%, preferably at least 75%, of the magnitude of b and which indicates the number of monomers contained in chemically bonded form in the polymer block [A].sub.a.