Granted Patent B2

US 8,013,081 · App. 12/083,995 · Granted Sep 6, 2011

Abstract

Claims (39)

1. A method for preparing emulsion polymer particles useful for opacifying, the method comprising:

polymerizing a first portion of a polymer sheath around a swellable polymer core in an emulsion;

treating the polymer core with a swelling agent to swell the polymer core;

adding non-homopolymerizing monomers to the emulsion containing the polymer core to retard or interrupt the polymerization of the polymer sheath;

after adding the non-homopolymerizing monomers, adding free monomers to the emulsion that are capable of copolymerizing with the non-homopolymerizing monomers; and

polymerizing the added free monomers and the non-homopolymerizing monomers to form a second portion of the polymer sheath.

2. The method of claim 1 , wherein the non-homopolymerizing monomers comprise a substance of the formula:

and anhydrides thereof;

wherein:

X are moieties independently selected from hydrogen, a halogen, or an organic group; and

at least two X moieties are selected independently from R 1 , COOR 2 , and Ar, wherein:

R 1 is an organic group;

R 2 is hydrogen, a halogen, or an organic group; and

Ar is a phenyl group of the chemical formula C 6 (R 3 ) 5 and R 3 are independently hydrogen, a halogen, or an organic group.

3. The method of claim 1 , wherein the non-homopolymerizing monomers comprise:

maleic anhydride;

non-homopolymerizing monomers of the formula C(Ar)(R 1 )═CH 2 ;

non-homopolymerizing monomers of the formula R 1 O(O)C—CH═CH—C(O)OR 2 ;

non-homopolymerizing monomers of the formula Ar—CH═CH—AR;

combination thereof; or

anhydrides thereof;

wherein Ar is a phenylu group of the chemical formula C 6 (R 3 ) 5 and R 1 , R 2 and R 3 are hydrogen, a halogen, or an organic group.

4. The method of claim 1 , wherein the non-homopolymerizing monomers added to the emulsion constitute at least about 3 parts by weight per 100 parts by weight of monomers used to polymerize the polymer sheath.

5. The method of claim 4 , wherein adding the non-homopolymerizing monomers to the emulsion comprises adding the non-homopolymerizing monomers to the emulsion in a burst charge.

6. The method of claim 1 , wherein adding the non-homopolymerizing monomers to emulsion reduces a glass transition temperature of the first portion of the polymer sheath to less than about a polymerization temperature of the first portion of the polymer sheath.

7. The method of claim 1 , wherein, upon drying, the polymer particles include voids that cause opacity in compositions containing the polymer particles.

8. The method of claim 1 , wherein the non-homopolymerizing monomers comprise alpha-methyl styrene.

9. The method of claim 1 , wherein the swelling agent comprises a base and the polymer core comprises a base-swellable polymer core.

10. The method of claim 9 , wherein the base and the non-homopolymerizing monomers are added at substantially the same time.

11. The method of claim 1 , wherein the emulsion is substantially free of inhibitors that inhibit free-radical polymerization of the polymer sheath at some stage.

12. The method of claim 1 , wherein polymerizing the polymer sheath around the swellable polymer core comprises free-radical polymerizing the polymer sheath around the polymer core.

13. A method for preparing emulsion opacifying polymer particles, the method comprising:

emulsion polymerizing a polymer core;

exposing the polymer core to a supply of free monomers to polymerize a first portion of a polymer sheath around the polymer core;

after polymerizing the first portion of the polymer sheath, exposing the polymer core to an amount of a swelling agent sufficient to swell the polymer core;

adding non-homopolymerizing monomers to retard or interrupt the polymerization of the first portion of the polymer sheath; and then

polymerizing additional free monomers and the non-homopolymerizing monomers into a second portion of the polymer sheath.

14. The method of claim 13 , wherein the non-homopolymerizing monomers added in the burst charge constitute at least about 3 parts by weight per 100 parts by weight of monomers used to form the polymer sheath.

15. The method of claim 14 , wherein exposing the polymer core to the amount of the swelling agent and changing the composition of the supply of free monomer are performed at substantially the same time.

Assignments (9)