CA1089577A - Freeze-thaw, stable, self-inverting water-in-oil, acrylamide polymer emulsions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A freeze-thaw stable, self-inverting, water-in-oil emulsion comprising an aqueous phase of a polymer of acrylamide, a hydrocarbon oil, a water-in-oil emulsifying agent and an inverting surfactant mixture com-prising sodium bis(2-ethylhexyl)sulfosuccinate and a sodium bis(C11-C15 alkyl) sulfosuccinate or an ethoxylated octyl or nonyl phenol and a method for the preparation thereof. The present emulsions do not form into clumps under alternate freezing and thawing conditions. They are useful as flocculants for sewage, cellulose fibers, metal ores, plating wastes, coal trailings, steel mill fines and potable water, for example.

Description

Emulsions of polyacrylamide, and copolymers of acrylamide with other copoly~erizable mono~ers, which are effective flocculants for many substrates inclu~ing sewage, cellulose fibers and fines for retention and freeness, metal ore treatment, plating waste, coal tailings, steel mill flue ducts and sinter fines, and potable water have becom~e increasingly important in recent years. These emulsions are usually of the water-in-oil variety and are inverted, by the addition of water thereto, to oil-in-water emulsions during which the polymer is rapidly dissolved in the ~ water. Emulsions and dissolution procedures of this type are disclosed in ; 10 United States Patent Nos. RE 28,474, 3,826,771 and 3,284,393.
While these emulsions are very effective when used as flocculants, they tend to be materially reduced in their e~fectiveness when they are ~;~
subjected to alternating freezing and thawing temperature such as would exist in m~ny areas during the winter season. The repeated temperature cycles tend to cause the emulsions to coagulate, i.e., form into large clumps of polymor rather than remain finely dispersed particles and, as a result, their usefulness as flocculating agents is drastically reduced.
The novel emulsions of the present invention exhibit excellent freeze-thaw properties, that is, they do not farm into clumps to the extent that they are rendered useless as flocculants when subjected to freeze-thaw ~' conditions. FurthermDre, they retain all the other attractive properties ' exhibited by existing emulsions such as high temperature stability, full inversion upon dilutian with water, good toleran oe to hard water and good s dispersion of oil-in-water after inversion (i.e., no separation or creaming of the oil phase).
This combination of excellent properties is achieved by the use of a critical inverting surfactant mixture.
The present invention provides a freeze-thaw stable, self-invert-ing, non-creaming, water-in-oil emulsion containing a dispersion therein of ; 30 finel~ divided poly~er particles, said emulsion comprising:
` (A) an aqueous phase ranging from about 70% to about 95%, by ;~` :
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(1) a water-soluble acrylamide polymer containing from about o% to about 35%, by weight of the polymer, of a oopolymeri-,~ zable monomer of an acrylic acid or methacrylamido-propyltri-methylammonium chloride, the acrylic acid in said polymer, if any, being fro.m about 50~" to about 100% ne~tralized, and having a concentration from about 27% to about 68%, by weigh~, based ~,~ on the total weight of A, and i (2) water in an a~ount ranging from about 32% to ab~ut 73%, 10 by weight, based o~ the total weight of A, s (B) a liquid hydrocarbon oil in an amount ranging from about 5%
~ to about 30%, by weight, based on the total weight of A and B, ':~
`~ (C) a water-in-oil emulsifying agent dispersed between said s aqueous phase and said liquid hydrocarbon at a concentration of about 0.1%
~, to about 15.0%, by weight, based on the total weight of A, s, C and.' (D) an inverting surfactant mixture co.mprising j~ (1) sodium bis(2-ethyLhexyl) sulfosuccinate and ~ (2) a sodium bis (Cll-C15 aIkyl) sulfosuccinate or an ethoxylat~
j~ ed octyl or nonyl phenol, the anLNnt of said sodium bis(2-ethylhexyl)sulfosuccinate ranging ~i from about 0.25% to about 1.5%, by weight, wnen said polymer is , cationic, and from about 2.8% to about 7.0%, by weight~ when A
~'. said polymer is anionic or non-ionic, the amount of said sodium ~5~ bis (Cll-C15 aIkyl) sulfosuccinate ranging from about 0.2% to ~i about 0.6%, by weight, and the amount of said ethoxylated octyl `i or nonyl phenol ranging from about 1.5% to about 2.5%, by weight, ~ said weight being based on the total weight of A, B, C and D.
i~.~ In another aspect, the present invention provides a method of preparing the freeze-thaw stable emLlsion described above which comprises:
~; 3Q (A) forming a water-in-oil enllsion of ~ (1) from about 70% to about 95%, by weight, based on the ,~ total weight of 1 and 2, of a solution of .... ..

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10~5~7~7 (a) a mixture of acrylamide and from about o% to about 35%i, by weight, based on the total weight of the mix-ture, of a copolymerizable monamer of an acrylic acid or methacrylamidopropyl trimethylammonium chloride, the acrylic acid, if any, being fmm about 50 - 75% neutralized, having a concentration from about 27% and akout 68%, by weight, based on the total weight of a and b, and . i .:
c (b) water, in an amount ranging from about 32%, to about 73~i, by weight, based on the total weight of a and b, ~i; 10 (2) a liquid hydrocarbon oil in an amount ranging from about 5% to about 30%, by weight, based on the total weight of 1 and

2,

(3) a water-in-oil emulsifying agent in a concentration of .~ , .
about 0.1% to about 15.0%, by weight, based on the total weight of 1, 2 and 3, and ;~
~' (4) a free radical initiator camprising sodium metabisulfate .$$ and a hydroperoxide, -(B) polymerizing said mono~ers under free-radical polymerizing conditions to form a water-in-oil emulsion which aontains dis- ~;
persed therein finely divided particles of a polymer of said acrylamide, and ! ;
~ (c) adding to said oil-in-water emulsion an inverting surfact- -~
;i ant mixture aomDrising ~`
(1) sodium bis(2-ethylh3xyl) sulfosuccinate and (2) a sodium bis (Cll-C15 alkyl) sulfosuccinate or an -~i~ ethoxylated nonyl or octyl phenol, i~ the ancNnt of said sodium bis(2-ethylhexyl)sulfosuccinate ranging from about ;
0.25% to about 1.5% by weight, when said comonamer is cationic, and fram about 2.8% to about 7.0%, by weight, when said oomonomer is anionic or non-3Q ionic or is absent, the am~unt of said sodium bis(Cll-C15 aLkyl) sulfo-suocinate ranging from about 0.2% to about 0.6~i, by weight, and the amount of said ethoxylats~d nonyl or octyl phenyl ranging from about 1.5% to about i ~ .

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1~9S'7~7' 2.5%, by weight, said weights being based on the total weight of said 1, 2, 3 and C.
As can be seen, the aqueous phase of my novel emNlsions is comprised of an acrylamide polymer and water. The polymer may oomprise polyacrylamide or a copolymer of acrylamide containing 65 - 98% of acryl-amide and 2 - 35~ of an acrylic acid or methacrylamidopropyl trimethyl-ammonium chloride. If an acrylic acid is used, it must be frcm about 50%
to about 100% neutralized to impart the freeze-thaw stability mentioned above to the final composition, the hlgher degree of neutralization being used when the acrylic acid content is below about 15%. Neutralization of the acrylic acid is preferably effected before the monamers are copoly-merized; however, it can be conducted after copolymerization, if desired.
Neutralization is effected by oontacting the acrylic acid monomer in aqueous solution with an appropriate amount of any known neutralization agent such as the alkali and alkaline earth metal hydroxides, ammonium hydroxide, amines and the like, as is known in the art. m e pH of the resultant aqu-eous phase will then range fram about 4.5 to about 5.5.
In the preferred sequence, the acrylamide, alone or with the oomonomer, is dissolved in water to attain the desired solids ooncentration and a suitable chelating agent - 3~ -¢'i -::
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- l(lb~9S77 such as ethylenediaminetetraacetic acid disodium salt is added to chelate metal ions which may be present in the system such as that which may have been incorporated into the acrylamide during its procluction. The neutralization of the acrylic acid, if present, follows, a small amount of iron preferably being added as a component of the initiator system, as more fully discussed hereinbelow. The oxidant part of the redox (as discussed below) catalyst system is ` preferably added to the aqueous phase at this time, or later ! 1 as described below.
, After the aqueous phase has been formed as above, it is homogenized into the oil phase which, at this time, con-stitutes a solution of the oil and a water-in-oil emulsifier.
Any known oil may be used for this purpose such as those set forth in the above incorporated U. S. patents. A preferred ~` oil useful for this purpose is a commercially available prod-uct sold under the trademark AMSCO OMS by the Union Oil Co.
of ~alifornia. It is a clear, oily liquid comprising approxi-' mately 86.9% paraffins, 13.0% naphthenes and 0.1% aromatics.
; 20 It has a molecular weight of about 170, a Specific Gravity of 0.755 at 60F., a Viscosity of 1.4 cps. at 77F., a Freez-ing Point below -25F., a Boiling Point of 399F., a Flash Point TCC of 126F. and is insoluble in water. Its Specific ~, Heat is 0.499BTU/16.F. at 100F. and 0.588 BTUjl6.F. at 200F
Any available water-in-oil emulsifier may be em-ployed, those set forth in the above U. S. Patents being ~, exemplary. A preferred emulsifier is sorbitan monooleate.
' After the water-in-oil emulsion is formed by agi-tation of the oil and water phases to insure uniform blend-ing, the oxidant part of the redox catalyst system may be i; .
¢ added, if it had not been added previously as described . ,~. .
~ above. This ingredient is added as an aqueous solution of ~ .
~ 4 , 10~9S~-~'7 the monomer emulsion in its complete concentration, i.e., from about 10 parts to about 500 parts per million parts of rmono-mers, preferably 25-150 pprn. ~ny redox c~talyst systcm can be used herein such as the bromate-sulfite systems; the peroxide-sulfite systems; the hydroperoxide-bisulfite systems, etc. Additionally, other free-radical catalyst systems may be employed, e.g., azobisisohutyronitrilc, bcnzoyl peroxide, lauroyl peroxide; potassium persulfate and the like as is known in the art. When the single component catalyst systems are employed, they are not added to the monomer emulsion un-til conversion of the monomers to polymer is desired. In the preferred aspect of this invention, however, the oxidant portion of a redox catalyst system comprising t-butyl hydro-~ peroxide and sodium metabisulfite, is added to the monomer i 15 emulsion first. The catalyst system preferably also utilizes , from about 1 ppm to about 10 ppm of iron, based on monomers, r as a component thereof, which iron can be extraneously added ~` to the aqueous phase as mentioned above or can be present as an inherent ingredient in the water or monomers per se. The reducing portion of the redox catalyst should be employed in amounts ranging from about 10 ppm to about 500 ppm based on monomers, preferably 50-200 ppm.
After the reaction mixture is prepared in the above manner, the system is then sparged with nitrogen gas to remove all oxygen from the system and the reducing portion ~- of the catalyst system is then pumped into the monomer emulsion containing the oxidant portion of thc catalyst ovcr a period of from about 2 to about 24 hours, i.e., until ~ substantial]y completc conversion i9 accomplislled, preEer~
,, 30 ably ahout 4-lG hours, the ]onger timeS being necessitatedby the lower concentration o catalyst and vice versa. The .' temperature of the reaction media should be maintained at ~5~
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from about 25C. ~o about 55C., prefcrabLy 35~ 5C.
After the catalyst component has been added and polymerization is substantially complete, stabilization of the resultant polymer is effectecl by thc addition of a further quantity of sodium metabisulfite, i.e., the reducing portion of the catalyst at polymerization temperature to stabilize the polymer.
The novel, so-called one-package, emulsion of the present invention, so called because inversion thereof can be accompl~shed by the addition of water only, is then pro-`~ duced by adding the above-described inverting suractant .~
mixture thereto.
: The amount of the sodium bis(2-ethylhexyl)sulfo-succinate component of the inverting surfactant mixture ~ 15 employed depends upon whether the polymer in the aqueous .. ~. , , phase is cationic, anionic or non-ionic. If the polymer is cationic, the sodium bis(2-ethylhexyl)sulfosuccinate is em-ployed in amounts ranging from about 0.25% to about 1.5~, preferably about 0.35% to about 0.75%, by weight, based on the total weight of the emulsion, i.e., components A, B, C and D, above. When the homopolymer or copolymer in the ' aqueous phase is anionic or non-ionic, the amount of sodium bis(2-ethylhexyl)sulfosuccinate should range from about 2.8%
to about 7.0%, preferably about 3.0% to about 4.5%, by weight, same basis. The sodium bis(2-ethylhexyl)sulfosuccinate may be used per se or as a solution in an oil. Suitable oils ~, include those set forth in the above patents and the above disclosure, the concentration in the oil ranging from about 25% to about 50%.
As mcntioned above, the second component of the inverting surfactant mixture comprises either a sodium ~s bis(Cll-C15 alkyl)suleosuccinate or an ethoxylated octyl ~',. : .
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or non~1 phenol. ~xalnples of suita~)le sodium bis(C11-C
alkyl)sulfosuc~inat~s inclucle ~o~iurn bis(undecyl)sulfo-succinate, sodium bis(tridecyl)sulfosucc~inate, sodium bis(penta-decyl)sulfosuccinate and the like. This component is in-corporated into tlle emulsion in an amount ranging from about 0.2~ to about 0. 6o / pre~erably ~rom about o.3'., t~ about 0.5~, by weight, based on the total wcight of thc emulsion, i.e.
components ~, B, C and D above.
The ethoxylated octyl or nonyl phenols useful as the second component in the inverting surfactant mixture comprises the reaction product of about one mole of octyl or nonyl phenol with from about 5-10 moles, preferably about 6-8 moles, of ethylene oxide. These materials are well known in the art as represented by the above set forth ; 15 U. S. patents. The ethoxylated octyl and nonyl phenols are employed in amounts ranging from about 1.5% to about 2.5%, by weight, preferably about 2~0~o~ by weight, again based on the total weight of the emulsion, i.e., components A, ~, C and D above.
The following examples are set forth for purposes -of illustration only and are not to be construed as limita-tions on the present invention except as set forth in the appended claims. All parts and percentages are by weight unless otherwise specificd.
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o a suitable reaction vcssel are aclded 2100.0 parts of acrylamide, as a 50.47~0 aqueous solution, and 850.0 parts of deionized water. To this solution is added 2.12 parts of the disodium salt of ethylenediamine tetraacetic acid and 1.15 parts of hydrated ferric sulfate (72~o Fe2(S04)3 used as 4.5 parts/1000 parts ~120) 'I'he pll of the resultant solution ls ad~usted to 5Ø l`llis constiLutes the aqueous mononler pllase.

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1~'3'~ 7 The oil ~has~ is ~r~E~ar~d by dissolving 90.0 parts of sorbitan monooleate in l040.0 ~arts of ~MSCO OMS, a com-mercially available, clear oily liquid sold by Union Oil Co. of California.
o a suitable, high speed homogerlizer is added thc complete oil phase system. The homogenizer is started and the monomer a~ueous phase is slowly added thereto to form an emulsion having a viscosity of 99o cps. The disperscd phase of the resultant emulsion has a particle size of about i lO 2.5 microns or less.
To a suitable reaction vessel is added the com-plete emulsion system with stirring. 70.0 Parts per million ~ (based on monomer) of t-butyl hydroperoxide are added. The 3 resultant media is purged with nitrogen gas to remove oxygen from the system. Stirring continues ! and sodium metabisul-:- fite is slowly pumped into the vessel over a period of 6 hours while maintaining the vessel at about 40C. after which about 100 parts per million (based on monomer) have been added. The resultant viscous emulsion exhibits 99.49~ con-version of acrylamide. The polymer solids are 25.54~ and the Standard Viscosity is 5.04 cps. The p~ is 7.4.
Stabilization of the polymer emulsion is accomplished by adding 78.28 parts of a 30% aqueous sodium metabisulfite solution. The emulsion is maintained under polymerizing ~ -: ~ .
conditions (60 minutes at 40C.) to substantially completely react the remaining acrylamlde. 0.4~ of the emulsion com-prises bisulfite which effects stabilization of the polymer .? system.
To the resultant polymer emulsioll are added, as an invcrting agerlt mixture over a period of 30 minutes, 5.5% of - a 70~, solution of sodium bis(2-ethylhexyl)sulfosuccinate in AMSCO OMS and 2.0~ of the reaction product of one mole of T:

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octyl phenol and 7.5 mo]es o[ e~hylelle oxide. Tl-e resultant emulsion is held at 40C. for an additiollal hour after which time the product is smooth and particle ~ree. The dispersed polymer pllase llas a particlc si ze of 2.5 microns or less.
S The ~tandard Viscosity is 5.15 cps. The Final uolymer solids content is 23.70~.
25.0 Parts of the final cmulsion are placed in a suitable vessel and subjected to a temperature of -10C. for 22 hours. I'he cold vessel is allowed to warm to room temper-l lO ature over 2 hours and a count is made of the macroscopic ¦ coagulated partlcles therein by pouring the emulsion slowly into a second vessel and counting the particles as tiley pass from one vessel to the other. After the count is es-tablished, the entire emulsion is returned to the first lS vessel and held again at -10C. for 22 hours. The cycle is continued for 17 days. The results are set forth in Table I
below. Weekly cycles were frozen and thawed at weekly in-¦ tervals at 0C.-10C. and -20C. These results are also set forth in Table I.

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" ' : ' . : ., 10~) 7'7 ~ second portion oF ~he emulsion of Example 1 is subjected to hic3h temperature to determine its stability toward loss of molecular w~i~ht as mea~ured by Starlclard Viscosity. The 50C. arld ~,oo~. results arc set fortll in TABLE II below. Failurc is determin~d to be a loss of about 20% of th~ initial Standclrcl Viscosity set Eorth abovc.
T~L~ II
~MULSION OF ~XAMPI.E~ I
Week No. 50C. 60C.
1 -- 5.05 2 -- 4.81 3 -- 4.55 4 -~ 4.41 -- 4.03 6 4.93 7 4.70 ,~ 8 4.46 9 4.40 4.16 ., Inversion of a third portion of the emulsion of Example,I is effected by injecting the portion into rapidly agitated water and continuing the agitation for 10 minutes.
Inversion is substantially complete within about 30 minutes.
The third sample above exhibits no separation (creaming) after standing at room temperature for 72 hours indicating excellent dispersion of the oil in the water c ' phase. Creaming is defined as a separation of the dispersed '' oil particle~ towards the upper portion of the contcnts oE
the container. Omi.sc~,ion of the ethylenc oxide reaction product rcsult~ in a dense cream lormation af,ter standinc~
4-5 hours. ~ny creaming whicll occurs rc(3arclinc3 the third _ ] ~ _ ' s, , -:
s lO~':t5'77 sample is rea~ily redisL)ersil)le ~ith very mild agitation.
Even severe ac~itation of the comparative sample wlthout the ethyl~ne oxide rcactiorl product therein docs not cause satisfactory redispersion oE ~he cream.
EXAMPl I'.';_2 cls~d 3 The proccdure of Example ~ is a~3ain followcd ex-cept that the ethylene oxide reaction product is produced from (2) one mole of octylphenol and 9.5 moles of ethylene oxide and (3) one mole of octylphenol and 5 moles of ethylene oxide. The results are set forth in TABLE III
below. The initial viscosity of the product of Example II
is 5.16 cps and that of Example III is 4.43 cps.

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The ~rocedure of ExamL~.Lc 1 :is repeated except that acrylic ac.id .is aclded as a comonomer in an amount such that the total. parts of rnonomer is equal but the mono-mer composition is 97/3 mol.e ratio of acryl.amide to acrylic acid and the acrylic aci.(l -is 10()~, neutrali.zcd. '~`he initial viscosity is 4.97 cps. 1`he results are set fortll in ~ .
TABLE IV.
. .
T~BLE: IV
--Freeze-Thaw Weekly q'hermal Cycles Daily Wee~ly Stabili-ty ~ 0C -10C -20C 50C 60C-.~ Initial 5 . 9 2 j 1 22 5 7 2 -- 5.03 , 15 2 23 6 9 4 -- 3.40 3 21 17 27 10 - 5.25 4 25 19 50 22 5.01 28 21 -- 33 3.20 j 20 EXAMPLE 5 ,! The procedure of Example ] is again followed except that the ethylene oxide reaction product is replaced by the ~, reaction product of one mole of nonyl~)henol with six moles ? of ethylene oxide. Thc l)aily frceze-thaw cycle (-10C) parti-cle count is 3(initial), 23, 37, 45, 32, 33, 36, 29, 29, 49.

. The Weekly freeze-thaw cycle (0C) particle count (3 initial) is 26 after eight weekly cycles; at -10C (1 ini-tial) is 34 after 7 weekly cycles; at -20C (1 initial) is 41 after 4 weekly cycles. The Weekly Thermal Stahili~y at 60C (Ini.tial Viscoslty 4.98 cps) :i.s 4.26 after 6 weeks.

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~gain the proce~ure of Example 1 is ~ollowed ex-cept that t~e ethylene oxide reaction product is replaced by 0.5% of soclium bis(tridecyl)sul~osuccinLIt~. The ~aily freeze-thaw cycle (-10C) particle count is l(initial), 3, 2, 3, 3, 5, 8, 7, 8, 10, 14, 18, 12, 14, 15, 14.
The Weekly ~reeæe-thaw cycle (0C) particlc count (3 initial) is 21 after 8 weekly cycles; at -10C (2 initial) is 12 after 8 weekly cycles; at -20C (0 initial) is 14 after 8 weekly cycles. The Weekly Thermal Stability (Initial Viscosity 4.98 cps) at 60C is 3.89 cps after 4 weeks; at 50C is 3.80 cps after 5 weeks; at 40C is 4.35 cps after 8 weeks.

Again following the procedure of Example 1 except that methacrylamidopropyl trime~thylammonium chloride ` is added as a comonomer in an amount such that the total parts of monomer is equal but the monomer composition is 90/10 mole ratio of acrylamide to chloride. Substantially identical results are achieved.

The procedure of Example 4 is again followed except that the acrylic acid content of the monomer composition is '; 70/30 and the degree of neutralization is 60~. Tests of the result emulsion indicate substantially the same results.
EXAMPLE 9 ;~
Methacrylic acid is substituted for acrylic acid in Example 1. Results are substantially equivalent.
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E X~MPI, E S_1 O_AN D 1 1 Following the proccdurc o~ ~.xample 6 except that (10) sodium ~is(triundecyl)sulfosuccinate and (11) sodium bis(tripentadecyl)sulfosuccin~te are used, substantially identi.cal results are achieved.

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Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A freeze-thaw stable, self-inverting, non-creaming, water-in-oil emulsion containing a dispersion therein of finely-divided polymer particles said emulsion comprising:
A. an aqueous phase ranging from about 70% to about 95%, by weight, based on the total weight of A and B, which is comprised of:
(1) a water-soluble acrylamide polymer containing from about 0% to about 35%, by weight of the polymer, of a copolymerizable monomer of an acrylic acid or methacrylamido-propyltrimethylammonium chloride, the acrylic acid in said polymer, if any, being from about 50% to about 100%
neutralized, and having a concentration from about 27% to about 68%, by weight, based on the total weight of A, and (2) water in an amount ranging from about 32% to about 73%, by weight, based on the total weight of A, B. a liquid hydrocarbon oil in an amount ranging from about 5% to about 30%, by weight, based on the total weight of A and B, C. a water-in-oil emulsifying agent dispersed between said aqueous phase and said liquid hydrocarbon at a concentration of about 0.1%
to about 15.5%, by weight, based on the total weight of A, B, C and D. an inverting surfactant mixture comprising (1) sodium bis(2-ethylhexyl) sulfosuccinate and (2) a sodium bis(C11-C15 alkyl) sulfosuccinate or an ethoxylated octyl or nonyl phenol, the amount of said sodium bis(2-ethylhexyl)sulfosuccinate ranging from about 0.25% to about 1.5%, by weight, when said polymer is cationic, and from about 2.8%, to about 7.0%, by weight, when said polymer is anionic or non-ionic, the amount of said sodium bis(C11-C15 alkyl) sulfosuccinate ranging from about 0.2% to about 0.6%, by weight, and the amount of said ethoxy-lated octyl or nonyl phenol ranging from about 1.5%
to about 2.5%, by weight, said weight being based on the total weight of A, B, C and D.

2. An emulsion according to Claim 1 wherein said polymer comprises about 70% acrylamide and about 30% acrylic acid.

3. An emulsion according to Claim 1 wherein said polymer comprises about 75% acrylamide and about 25% metha-crylamidopropyl trimethyl ammonium chloride.

4. An emulsion according to Claim 1 wherein said polymer comprises about 97% acrylamide and about 3% acrylic acid.

5. An emulsion according to Claim 1 wherein said polymer is polyacrylamide.

6. An emulsion according to Claim 1 wherein said inverting surfactant mixture comprises sodium bis(2-ethyl-hexyl)sulfofuccinate and sodium bis(tridecyl)sulfosuccinate.

7. An emulsion according to Claim 1 wherein said inverting surfactant mixture comprises sodium bis(2-ethylhexyl) sulfosuccinate and the reaction product of about one mole of nonyl phenol with about six moles of ethylene oxide.

8. An emulsion according to Claim 1 wherein said inverting surfactant mixture comprises sodium bis(2-ethyl-hexyl)sulfosuccinate and the reaction product of about one mole of ocyl phenol with about 7.5 moles of ethylene oxide.

9. A method of preparing the freeze-thaw stable emulsion of Claim 1 which comprises:
A. forming a water-in-oil emulsion of (1) from about 70% to about 95%, by weight, based on the total weight of 1 and 2, of a so-lution of (a) a mixture of acrylamide and from about 0% to about 35%, by weight, based on the total weight of the mixture, of a copolymerizable monomer of an acry-lic acid or methacrylamidopropyl trimethyl-.
ammonium chloride, the acrylic acid, if any, being from about 50-75% neutralized, having a concentration from about 27% and about 68%, by weight, based on the total weight .
of a and b, and (b) water, in an amount ranging from about 32%, to about 73%, by weight, based on the total weight of a and b, (2) a liquid hydrocarbon oil in an amount ranging from about 5% to about 30%, by weight, based on the total weight of 1 and 2, (3) a water-in-oil emulsifying agent in a concentration of about 0.1% to about 15.0%, by weight, based on the total weight of 1, 2 and 3, and (4) a free radical initiator comprising sodium metabisulfite and a hydroperoxide, B. polymerizing said monomers under free--radical polymerizing conditions to form a water--in-oil emulsion which contains dispersed therein finely divided particles of a polymer of said acrylamide, and C. adding to said oil-in-water emulsion an inverting surfactant mixture comprising sodium bis(2-ethylhexyl)sulfosuccinate and a sodium bis(C11-C15 alkyl)sulfosuccinate or an ethoxylated nonyl or octyl phenol, the amount of said sodium bis(2-ethylhexyl)sulfosuccinate ranging from about 0.25% to about 1.5%, by weight, when said comonomer is cationic, and from about 2.8% to about 7.0%, by weight, when said comonomer is anionic or non-ionic or is absent, the amount of said sodium bis(C11-C15 alkyl)sulfosuccinate ranging from about 0.2% to about 0.6%, by weight, and the amount of said ethoxylated nonyl or octyl phenyl ranging from about 1.5% to about 2.5%, by weight, said weights being based on the total weight of said 1, 2, 3 and C.

10. A method according to Claim 9 wherein said monomer mixture comprises about 70% acrylamide and about 30% of an acrylic acid.

11. A method according to Claim 9 wherein said monomer mixture comprises about 75% acrylamide and about 25% of methacrylamidopropyl trimethylammonium chloride.

12. A method according to Claim 9 wherein said monomer mixture comprises about 97% acrylamide and about 3% acrylic acid.

13. A method according to Claim 9 wherein said monomer comprises acrylamide.

14. A method according to Claim 9 wherein said inverting surfactant mixture comprises sodium bis(2-ethyl-hexyl)sulfosuccinate and sodium bis(tridecyl)sulfosuccinate.

15. A method according to Claim 9 wherein said inverting surfactant mixture comprises sodium bis(2-ethyl-hexyl)sulfosuccinate and the reaction product of about one mole of nonyl phenol and about 6 moles of ethylene oxide.

16. A method according to Claim 9 wherein said inverting surfactant mixture comprises sodium bis(2-ethyl-hexyl)sulfosuccinate and the reaction product of about one mole of octyl phenol and about 7.5 moles of ethylene oxide.