Multistage process for producing polymer dispersion of discrete particles
The present invention relates to a multistage radical emulsion polymerization process for producing a polymer dispersion of discrete particles dispersed in water, thereby producing a novel star shaped polymer composition, where the wet and dry properties of the dispersion polymer obtained by radical emulsion polymerization in water are modified. The present invention also relates to its use in coating, textile and adhesive applications.
1 . A multistage radical emulsion polymerization process for producing a polymer dispersion of discrete particles dispersed in water, said process comprising the steps of;
polymerizing in a first stage a core of the discrete particles, as the main polymeric part comprising from 0 to 4.5% by weight of one or more monoethylenically unsaturated monomers containing an acidic functional group based on the total monomer composition of the main polymeric part,
polymerizing in a second stage a swellable/soluble outer layer as the second polymeric part comprising at least 5% by weight of one or more monoethylenically unsaturated monomers containing an acidic functional group based on the total monomer composition of the swellable/soluble outer layer, and non-acid-functional monomers completing the outer layer composition up to 100% by weight, the non-acid functional monomers being selected from monomer combinations capable of copolymerizing with a carboxylic functional monomer(s),
wherein up to 30% by weight of the non-acid-functional monomers are monomers having a functionality that confers or enhances a specific property of the outer layer, said non-acid-functional monomers being selected from nitrogen-containing monomers, epoxy, hydroxy and carbonyl functional monomers, polyunsaturated monomers, dicarbonyl monomers, silane-functional monomers, and phosphate-functional monomers,
wherein the swellable/soluble outer polymeric layer is polymerized onto the surface of the main polymeric part, wherein the amount of swellable/soluble outer layer represents between 3% to 50% by weight of the total polymeric composition,
and adding a swelling agent selected from a base in sufficient amount as to raise the pH and bring the swellable/soluble outer layer (SOL) to the desired degree of swelling or dissolution,
whereby that outer layer undergoes swelling or dissolving when submitted to a pH change, while the main polymeric part remains substantially unaffected.
2 . The process according to claim 1 wherein the swellable/soluble outer layer has a pH-sensitive polymer composition, in the sense that an increase in pH above 6 causes the swellable/soluble outer layer to swell or, eventually, to dissolve.
3 . The process according to claim 1 wherein the amount of swellable/soluble outer layer represents between 5% to 30% by weight of the total polymeric composition.
4 . The process according to claim 1 wherein the amount of swellable/soluble outer layer represents between 7.5% to 25% by weight of the total polymeric composition.
5 . The process according to claim 1 wherein the swellable/soluble outer layer is a polymer containing from 5% to 30% by weight of one or more mono- or di-carboxylic monomer, their anhydrides and their salts, based on the total monomer composition of the swellable/soluble outer layer.
6 . The process according to claim 5 wherein the carboxylic-functional monomer is selected from acrylic acid, methacrylic acid, itaconic acid or crotonic acid.
7 . The process according to claim 1 wherein the non-acid-functional monomer(s) completing the composition of the swellable/soluble outer layer are selected from C 1 to C 16 monomers.
8 . The process according to claim 1 wherein in the second stage, the one or more monoethylenically unsaturated monomers containing an acidic functional group is from 7.5% to 25% by weight based on the total monomer composition of the swellable/soluble outer layer polymerized in the second stage.
9 . The process according to claim 1 wherein in the second stage, the one or more monoethylenically unsaturated monomers containing an acidic functional group is at least 10% by weight based on the total monomer composition of the swellable/soluble outer layer polymerized in the second stage.
10 . A polymer dispersion of discrete particles dispersed in water obtained by the process according to claim 1 .
11 . A method of using the polymer dispersion of claim 1 , as an adhesive, coating or textile treatment said method comprising applying the polymer dispersion to a substrate.