Patent ID: 6262144
Filing Date: 2001-07-17
Classification: C08F,C09D,C09J,D21H,Y10S

Abstract:
A process for preparing aqueous polymer dispersions, where first monomers having at least one ethylenically unsaturated group are polymerized by the method of free-radical aqueous emulsion polymerization to give a polymer 1, in dispersed distribution in the aqueous medium, and then, in one or more successive polymerization stages i, further monomers are subjected to free-radical polymerization in the presence of the polymer 1 that is in disperse distribution in the aqueous medium, with the proviso thata) the polymer 1 has a glass transition temperature Tg.sup.1 ;b) the monomers polymerized in each of the polymerization stages i are such that isolated random copolymerization of these monomers would give a polymer i whose glass transition temperature tends with increasing molecular weight toward the limit value Tg.sup.i ;c) for each Tg.sup.i the difference Tg.sup.i -Tg.sup.1 is .gtoreq.10.degree. C.;d) the amount of the monomers polymerized to prepare the polymer 1 in disperse distribution, based on the amount of all of the monomers polymerized in the process, is .gtoreq.90% by weight and .ltoreq.99.9% by weight;e) the total amount of the monomers polymerized in all polymerization stages i, based on the total amount of all of the monomers polymerized in the process, is .gtoreq.0.1% by weight and .ltoreq.10% by weight;f) in each of the polymerization stages i, the addition of the monomers i to the polymerization vessel is made such that at no time up to the end of the addition does the degree of polymerization U.sup.i of monomers i exceed 50 mol-%;g) the total amount of the monomers polymerized to prepare the polymer 1, apart from the monomers having two conjugated ethylenically unsaturated groups, does not include more than 5% by weight of monomers having more than one ethylenically unsaturated group; andwherein in each of the polymerization stages i the monomers are added in pure form.