Patent Number: 045254966
Section: claims

1. A self-inverting, stable water-in-oil emulsion comprising (1) a discontinuous aqueous phase containing a water-soluble polymer which discontinuous phase is dispersed in (2) a continuous oil phase wherein the emulsion contains an inverting amount of an inverting surfactant and an emulsifying amount of a water-in-oil emulsifier, said emulsion having been prepared by polymerizing a water-in-oil emulsion of a water-soluble ethylenically unsaturated monomer containing a portion of the inverting surfactant and adding the remainder of said inverting surfactant to the resultant water-in-oil emulsion of water-soluble polymer subsequent to polymerization, said portion added prior to the completion of polymerization being a sufficient amount of a nonionic surfactant to increase the degree of inversion when the water-in-oil emulsion of water-soluble polymer is inverted into a continuous aqueous phase. 2. The emulsion of claim 1 wherein the emulsion is inverted into a continuous aqueous phase containing from about 0.001 to about 10 weight percent of a dissolved salt. 3. The emulsion of claim 1 wherein the polymer is polyacrylamide or a copolymer or acrylamide and acrylic acid. 4. The emulsion of claim 1 wherein the polymer is a copolymer of acrylamide and a water-soluble cationic comonomer. 5. The emulsion of claim 1 wherein the inverting surfactant is a water-soluble nonionic surfactant. 6. The emulsion of claim 5 wherein the surfactant is an alkyl polyethyleneoxy alcohol or an alkylphenoxy alcohol. 7. The emulsion of claim 6 wherein the surfactant has an HLB in the range from about 10 to about 14. 8. The emulsion of claim 1 wherein the portion of inverting surfactant added prior to polymerization is in the range from about 0.05 to about 5 weight percent based on the monomer weight. 9. The emulsion of claim 1 wherein the remainder of inverting surfactant added to the emulsion subsequent to polymerization is in the range from about 0.5 to 10 weight percent based on the monomer weight. 10. A process for preparing the water-in-oil emulsion of claim 1 which comprises (1) forming a stable water-in-oil emulsion (monomeric precursor) containing at least one water-soluble monomer in the aqueous phase which is dispersed in a continuous aqueous, phase said emulsion containing an emulsifying amount of a water-in-oil emulsifier and an amount of an inverting surfactant that is sufficient to increase the degree of inversion when the emulsion of water-soluble polymer is inverted; (2) subjecting the monomeric precursor to conditions sufficient to polymerize the monomer; and (3) adding a remaining amount of an inverting surfactant which will enable the water-in-oil emulsion of the polymer to invert upon the addition of sufficient water. 11. A process for inverting the water-in-oil emulsion of claim 1 which comprises dispersing the emulsion in a continuous aqueous phase such that the water-soluble polymer is intimately dispersed in said continuous aqueous phase. 12. The emulsion of claim 1 wherein the nonionic surfactant is an alkyl polyethyleneoxy alcohol represented by the formula: R--(EO).sub.n H wherein R is C.sub.4 -C.sub.20 alkyl, EO is ethyleneoxy and n is a number from 1 to 10. 13. The emulsion of claim 1 wherein the nonionic surfactant is a polyethylene glycol ether of a secondary alcohol. 14. The emulsion of claim 1 wherein the inverting surfactant is a polyethylene glycol ether of a secondary alcohol which is present in the amount from 3.5 to 5 weight percent and the emulsifier is a mixture of 2 weight percent of isopropanolamide of oleic acid and 2 weight percent of sorbitan monooleate, said percentages being based on the water-soluble monomer. 15. The emulsion of claim 14 wherein the monomer is a mixture of acrylamide and acrylic acid.