Redispersible powder and its aqueous dispersion, preparation process and use

Abstract

The invention relates to a redispersible powder obtainable by (co)polymerization, using a polymer with cationic functionality in an aqueous medium, optionally accompanied by the use of conventional additives, the polymer with cationic functionality being obtained by (co)polymerization in an aqueous medium of olefinically unsaturated (co)monomers, wherein at least one (co)monomer has a cationic functionality, further (co)monomers are added and polymerization takes place in the presence of suitable initiators, and by drying the aqueous dispersion obtained, the (co)polymerizate having one or more reactive groups. According to another embodiment, the polymer with cationic functionality is formed in situ in the presence of a seed. According to another embodiment, the process is controlled in such a way that a (co)polymerizate particle with heterogeneous morphology is formed. The invention also relates to the aqueous dispersions, a process for the preparation of the redispersible powder and the use thereof.

1 . A film-forming, redispersible polymer powder comprising particles with a heterogeneous morphology and having at least one polymer phase with a glass transition temperature of below +50° C., 
 wherein the powder having particles with heterogeneous morphology is formed by polymerization of at least one comonomer with at least one initiator in an aqueous medium in the presence of a polymer with cationic functionality having one or more reactive groups,    wherein the polymer with cationic functionality is obtained by polymerization in an aqueous medium of olefinically unsaturated monomers and by subsequently drying the aqueous dispersion,    and wherein the olefinically unsaturated monomers comprise a) at least one monomer having cationic functionality and at least one monomer having reactive groups or b) at least one monomer having cationic functionality and reactive groups.    
     
     
         2 . The redispersible powder of  claim 1  wherein at least one comonomer has at least one anionic functionality.  
     
     
         3 . The redispersible powder of  claim 1 , wherein the polymer is polymerized in situ in the presence of a seed monomer.  
     
     
         4 . The redispersible powder of  claim 1  wherein the polymer powder comprises latex particles having a core-shell morphology.  
     
     
         5 . The redispersible powder of  claim 4  wherein said latex particles have an average diameter of from 30 to 1000 nm.  
     
     
         6 . The redispersible powder of  claim 4  having a core-shell morphology comprising a hydrophillic inner phase and a hydrophobic outer phase.  
     
     
         7 . The redispersible powder of  claim 1  wherein said reactive functional groups are selected from the group consisting of hydroxyl, carboxyl, carboxyl ester, amino, ammonium, amide, silane, epoxide, carbonyl, formamide, acetamide, succinimide, epihalohydrin, and mixtures thereof.  
     
     
         8 . The redispersible powder of  claim 1  wherein said cationic functional monomer copolymer comprises 1 to 30 percent by weight of said copolymer.  
     
     
         9 . The redispersible powder of  claim 1  wherein said copolymer is formed from 10 to 100 percent by weight of monomers containing a reactive functional group.  
     
     
         10 . The redispersible powder of  claim 1  wherein said cationic monomer comprises a quaternary ammonium group.  
     
     
         11 . The redispersible powder of  claim 1  wherein said reactive functional groups are activated following a redispersion by a change in the pH of the redispersion.  
     
     
         12 . The redispersible powder of  claim 1  wherein said reactive functional group comprises at least one protonated group which is deprotonated by raising the pH-value of the redispersion.  
     
     
         13 . The redispersible powder of  claim 1  wherein said aqueous dispersion comprises less than 2.5% by weight of emulsifier.  
     
     
         14 . The redispersible powder of  claim 13  wherein said aqueous dispersion is free of emulsifier.  
     
     
         15 . The redispersible powder of  claim 1  wherein said drying is by spray or freeze drying.  
     
     
         16 . An aqueous dispersion comprising the redispersible powder of  claim 1 .  
     
     
         17 . A process for the preparation of the redispersible powder of  claim 1 , comprising the polymerization of at least one comonomer with at least one initiator in an aqueous medium, the polymerization being carried out in the presence of a polymer with cationic functionality having one or more reactive groups to form particles with heterogeneous morphology, 
 wherein the polymer with cationic functionality is obtained by polymerization in an aqueous medium of olefinically unsaturated monomers and by subsequently drying the aqueous dispersion,    and wherein the olefinically unsaturated monomers comprises a) at least one monomer having cationic functionality and at least one monomer having reactive groups or b) at least one monomer having cationic functionality and reactive groups.