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Abstract

The present invention relates to aqueous polymer dispersion of voided polymer particles and to a process for preparing such aqueous polymer dispersions. The present invention also relates to polymer particles, in particular powders of said polymer particles, which are obtained by drying a polymer dispersion. Further aspects of the present invention relate to the use of such voided polymer particles and the polymer dispersions as opacifiers and to paints containing such aqueous polymer dispersions. The voided polymer particles comprise: i) an alkali swellable polymer core of polymerized ethylenically unsaturated monomers M(i) comprising polymerized acid monomers M(i.ac) in an amount sufficient for allowing the polymer core to swell at a pH of at least pH 7.5; ii) an intermediate polymer layer of polymerized ethylenically unsaturated monomers M(ii); and iii) a polymer shell of polymerized ethylenically unsaturated monomers M(iii) having a theoretical glass transition temperature according to Fox of at least 60° C. where the monomers M(iii) comprise at least 10% b.w., based on the total weight of the monomers M(iii), of one or more monomers M(iii.a) whose homopolymers have a glass transition temperature of at least 50° C., where the monomer M(iii.a) is selected from the group consisting of C₅-C₂₀-cycloalkyl esters of acrylic acid, C₅-C₂₀-cycloalkyl esters of methacrylic acid, C₅-C₂₀-cycloalkylmethyl esters of acrylic acid, C₅-C₂₀-cycloalkylmethyl esters of methacrylic acid, where cycloalkyl in the aforementioned monomers is mono-, bi- or tricyclic and may be unsubstituted or carry 1, 2, 3 or 4 methyl groups; C₃-C₂₀-heterocycloalkyl esters of acrylic acid, C₃-C₂₀-heterocycloalkyl esters of methacrylic acid, C₃-C₂₀-heterocycloalkylmethyl esters of acrylic acid, C₃-C₂₀-heterocycloalkylmethyl esters of methacrylic acid, where heterocycloalkyl in the aforementioned monomers has a total of 5 to 16 ring-forming atoms, where 1, 2 or 3 non-adjacent ring-forming atoms are oxygen atoms while the remainder of the ring-forming atoms are carbon atoms, and where heterocycloalkyl is mono-, bi- or tricyclic and may be unsubstituted or carry 1, 2, 3 or 4 methyl groups; di-C₁-C₂-alkyl esters of itaconic acid; and combinations thereof.

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First Claim