Patent ID: 8268927

Claim:
A water redispersible polymer powder (RDP) comprising a co-dried admixture of: A) a water insoluble film-forming high T g polymer, said film forming polymer comprising a styrene-butadiene copolymer or the copolymerization product of styrene, butadiene and one or more other monomer and having a glass transition temperature (T g ) of greater than 15° C., an average particle size of from 50 nm to 500 nm, and an amount of carboxylation of from 0.1 wt. % to 10 wt. % of at least one ethylenically unsaturated mono- and/or di-carboxylic acid, salts thereof, or mixtures thereof, based upon the weight of the water insoluble film forming high T g polymer, and B) a water insoluble film-forming low T g polymer, said film forming polymer comprising a styrene-butadiene copolymer or the copolymerization product of styrene, butadiene and one or more other monomer and having a glass transition temperature (T g ) of from −30° C. to 10° C., an average particle size of from 20 nm to 400 nm, and an amount of carboxylation of from 0.1 wt. % to 10 wt. % of at least one ethylenically unsaturated mono- and/or di-carboxylic acid, salts thereof, or mixtures thereof, based upon the weight of the water insoluble film forming low T g polymer, wherein the ratio of the average particle size of the high T g polymer to the low T g polymer is from 1:1 to 5:1, and the amount of the high T g polymer is from 20 wt. % to 35 wt. %, based upon the total weight of the high T g polymer and the low T g polymer.