Aqueous dispersion of polymer additive and process for preparing the same

An aqueous dispersion of a polymer additive with a weight average molecular weight of from 2,000 to 25,000 g/mol, wherein the polymer additive comprises, by weight based on the weight of the polymer additive,

• (i) from 20% to 85% of structural units of an ethylenically unsaturated siloxane monomer of formula (I), (II), or (III),
• wherein, in formula (I), R is an ethylenically unsaturated group, and j and k are each independently in the range of from 0 to 100, and j+k=5 to 100;
• wherein, in formula (II), R is an ethylenically unsaturated group, R1 is a hydroxyl, alkyl, aryl, alkoxyl, aryloxy, alkyl ether, or aryl ether group, and m is from 1 to 100;
• wherein, in formula (III), R is an ethylenically unsaturated group, R1 and R2 are each independently a hydroxyl, alkyl, aryl, alkoxyl, aryloxy, alkyl ether, or aryl ether group, n is from 1 to 5, and p is from 1 to 100;
• (ii) from 0.1% to 10% of structural units of an ethylenically unsaturated functional monomer carrying at least one functional group selected from an amide, ureido, carboxyl, carboxylic anhydride, hydroxyl, phosphorus acid, or sulfonic acid group, a salt thereof, or mixtures thereof;
• and
• (iii) from 5% to 79.9% of structural units of an additional ethylenically unsaturated nonionic monomer;
• wherein the coagulum content of the aqueous dispersion is less than 2,000 ppm after filtration through a 44 micron sieve.