Inverse Emulsion Polymerization With Sorbitan Fatty Acid Esters and Ethoxylated Alcohol

In one aspect, this invention relates to a surfactant system which includes a blend of different surfactant compositions. According to another aspect, the invention relates to inverse emulsion polymerization using such a surfactant system.

Conventional emulsion polymerization generally has involved an oil phase finely dispersed in a continuous water phase. However with the production of water-soluble polymers a problem results in that the polymer as it is formed, being water-soluble, dissolves in the continuous water phase and increases the viscosity to an unacceptable extent. If dilute solutions are used, the cost of transportation is prohibitive.

It might seem, then, that the proper approach would be to form the polymer and separate it as a dry solid so that only the polymer has to be transported. However these types of polymers are hard to redissolve in water because the water surrounds the individual particles and swells the outer surface thus forming an "insulation" which greatly slows down the rate at which the polymer goes into solution.

It is known to use an inverse emulsion system wherein water-soluble polymers can be produced in a dispersed water phase within a continuous hydrocarbon phase. Here the polymer formed remains in the dispersed water droplets and does not significantly affect the viscosity of the emulsion. This not only offers an advantage over ordinary emulsions but offers an advantage over forming a dry product. This is because the inverse emulsion is of low viscosity for easy handling and can be quite concentrated for easy transportation. Then at the well site it is easily possible to dilute with a large quantity of water and break the emulsion. Since the polymer is formed in small droplets in the inverse emulsion and is already in solution it easily disperses in the water.

The prior art broadly discloses parameters which can be used to achieve inverse emulsions. U.S. Pat. No. 4,147,681 for instance discloses the use of a relatively high concentration of surfactants having a hydrophilic/lipophilic balance (HLB) of at least 7 to give a stable emulsion which can be inverted by dilution.

Recently, copolymer compositions based on certain monomers have been developed which are particularly suitable for high temperature utility. These polymers have high molecular weight and contain either N-vinyl lactam monomers such as N-vinylpyrrolidone or vinl-containing sulfonate monomers such as 2-acrylamido-2-methylpropane sulfonic acid or a salt thereof. For these polymers, suitable inverse emulsion polymerization techniques have proven especially difficult. Thus while such monomers are broadly mentioned in the art dealing with inverse emulsions, satisfactory techniques for inverse emulsion polymerization of these monomers to high molecular weight polymers has not heretofore been available.

It is an object of this invention to provide a stable inverse emulsion polymerization system for monomer compositions comprising an N-vinyl lactam and/or a vinyl-containing sulfonate thereof which monomers are used to make water-soluble polymers; and

It is a further object of this invention to provide an improved surfactant composition for inverse emulsion polymerization to produce water-soluble polymers.

The above objects are at least partially realized by a water-in-oil-emulsion polymerization process for making water-soluble polymers from a monomer system comprising at least one of an N-vinyl lactam and a vinyl-containing sulfonate comprising: combining an aqueous component, a hydrocarbon component, the monomer system, an initiator and a surfactant system, wherein the surfactant system comprises (1) a first surfactant composition having at least one surfactant characterized by a lipophilic portion and an OH-containing hydrophilic portion, the first composition having an HLB of about 7 to about 9; and (2) a second surfactant composition comprising at least one generally straight chain nonionic surfactant having a lipophilic hydrocarbon group and an OH terminated hydrophilic group, the second composition also having an HLB of about 7 to about 9.

According to another aspect of the invention, a surfactant system is provided which comprises: a first surfactant composition having an HLB of about 7 to about 9 comprising a blend of a sorbitan fatty acid ester and an ethoxylated sorbitan fatty acid ester, as hereinbelow defined; and a second surfactant composition having an HLB of about 7 to about 9 comprising an alkoxylated alcohol.

A substantial feature of this invention is the discovery that the prior art teachings as the the proper HLB to achieve the desired result are not entirely correct. Actually it is the right chemical type of surfactant composition having the right HLB which must be utilized. Even more unexpectedly, it has been found that for the type of system of this invention there must be a surfactant system of the right HLB made up of two different components each of the right chemical type.

As to the make-up of the surfactant system, the system comprises two different surfactant compositions hereinafter described.

The first surfactant composition comprises at least one surfactant which is characterized by a lipophilic portion and an OH-containing hydrophilic portion, and which is further characterized by an HLB of about 7 to about 9, most preferably 8 for the most stable emulsion. Although it is within the scope of certain aspects of the invention to use only one surfactant for the first composition, it is usually necessary to use a blend of surfactants to achieve the proper HLB.

One suitable first composition surfactant is a sorbitan fatty acid ester, which as used herein and in the appended claims is a fatty acid ester of sorbitan having the general formula

where R.sup.1 is a hydrocarbon group comprising a straight-chain of alkyl groups having 6 to 22 carbon atoms, and where n is an integer of 1 to 3. Such an ester results from the esterification of sorbitan (C.sub.6 H.sub.8 O(OH).sub.4), also called sorbitol anhydride, with n molecules of a fatty acid (RCOOH) such as lauric acid, stearic acid, oleic acid, etc. R.sup.1 can be considered the lipophilic portion and the remainder the hydrophilic portion. Several particularly suitable sorbitan fatty acid esters which are sold under the trademark "Span" by ICI Americans, Inc. are sorbitan monolaurate (Span 20) wherein R.sup.1 has 11 carbon atoms and n is 1, sorbitan monopalmitate (Span 40) wherein R.sup.1 has 15 carbon atoms and n is 1, sorbitan monostearate (Span 60) wherein R.sup.1 has 17 carbon atoms and n is 1, sorbitan tristearate (Span 65) wherein n is 3, sorbitan monooleate (Span 80) wherein R.sup.1 has 17 carbon atoms and n is 1, and sorbitan trioleate (Span 85) wherein n is 3. As is well known to those skilled in the art, the compound names are derived from the number and type of RCOO group(s) per molecule. For example, sorbitan monooleate includes one oleate group (oleic acid minus the terminal hydrogen), and thus has the formula C.sub.6 H.sub.8 O(OH).sub.3 (C.sub.17 H.sub.33 COO), or more accurately, C.sub.6 H.sub.8 O(OH).sub.3 (CH.sub.3 (CH.sub.2).sub.7 CH:CH(CH.sub.2).sub.7 COO).

Another particularly suitable first composition surfactant is a polyethoxylated sorbitan fatty acid ester which as used herein and in the appended claims is a polyethoxylated fatty acid ester of sorbitan having the general formula

wherein n is an integer from 1 to 3 as above, R.sup.1 is defined as above, and m is an integer from 4 to 20 and denotes the number of oxyethylene groups (OCH.sub.2 CH.sub.2). R.sup.1 is generally the lipophilic portion and the remainder the hydrophilic portion. Several suitable compounds which are sold under the trademark "Tween" by ICI Americas, Inc. are the following where the value of m is in parenthesis after "polyoxyethylene": polyoxyethylene (20) sorbitan monolaurate (Tween 20), polyoxyethylene (20) sorbitan monopalmitate (Tween 40), polyoxyethylene (20) sorbitan monostearate (Tween 60), polyoxyethylene (4) sorbitan monostearate (Tween 61), polyoxyethylene (20) sorbitan tristearate (Tween 65), polyoxyethylene (20) sorbitan monooleate (Tween 80), and polyoxyethylene (20) sorbitan trioleate (Tween 85).

Sorbitan fatty acid esters and polyethoxylated sorbitan fatty acid esters are the preferred compounds for the first surfactant composition. However to achieve the proper HLB, it is usually necessary to blend such esters. This is because the sorbitan fatty acid esters have low HLB values, predominantly under 8, and polyethoxylated sorbitan fatty acid esters have high HLB values above 9.

Other surfactants can be employed according to certain aspects of the invention for use as the first surfactant composition. One example is a class of compounds called polyethoxy substituted phenols commercially available under the trademark "Triton" from Rohm and Haas Co. Specific examples include polyethoxy octyl phenol (Triton X-15) and polyethoxy nonyl phenol (Triton N). Like the ester compounds discussed above, the polyethoxy substituted phenols are usually blended to achieve the proper HLB.

The second surfactant composition comprises at least one generally straight-chain nonionic surfactant characterized by a lipophilic portion and an OH terminated hydrophilic portion and further being characterized by an HLB of about 7 to about 9, preferably about 8.

Preferably, a straight-chain hydrocarbon group constitutes the lipophilic portion and a straight-chain alkoxy group terminated by an OH group constitutes the hydrophilic portion. Of the general class of such alkoxylated compounds, ethoxylated alcohols are presently preferred as giving the most stable emulsions. Ethoxylated alcohols can be represented by the general formula

where R.sup.2 is a 10 to 30 carbon atom hydrocarbon group, preferably a straight-chain 16-18 atom hydrocarbon group, and x is an integer from 1 to 50, preferably 4. Where R.sup.2 has 16-18 carbon atoms and x is 4, this constitutes a polyethoxylated alcohol having an HLB of about 8 available under the trademark "Siponic E-2" from Alcolac, Inc. This compound blended with the first composition has been found to give highly stable emulsions which yield polymers which give desirably high viscosity polymer solutions in brine, especially where a blend of the above described esters is used as the first composition (Span and Tween). Other suitable Siponic polyethoxylated alcohols include polyoxyethylene(2)cetyl alcohol (Siponic C-20) and polyoxyethylene cetyl/stearyl alcohol (Siponic E-10) both of which are usually blended to achieve the proper HLB. Yet other suitable compounds under the ethoxylated alcohol general formula include compounds sold under the trademark "Brij" by ICI Americas, Inc., such as Brij 72 (R.sup.2 has 18 carbons, and x is 2) and Brij 78 (R.sup.2 has 18 carbons and x is 20) which also must normally be blended to achieve the proper HLB.

Other alkoxylated compounds suitable for use for the second surfactant composition are ethoxylated fatty acids sold under the trademark "Pegosperse" by Glyco Chemicals, Inc. and ethoxylated amines.

Suitable initiators for inverse polymerization include azo compounds such as 2,2'-azobisisobutyronitrile (commercially available as Vazo-64.RTM. from E. I. DuPont), 2-t-butylazo-2-cyanopropane, 2,2'-azobis(2,4-dimethylvaleronitrile) (Vazo-52.RTM. from E. I. DuPont), 2,2'-azobis(2-amidinopropane)hydrochloride (V-50 from Wako), 2-t-butylazo-2-cyanopropane, 2-t-butylazo-2-cyanobutane, b 2-t-butylazo-1-cyanocyclohexane, 2-t-butylazo-2-cyano-4-methoxy-4-methylpentane (commercially available as Luazo.RTM. 55 from Lucidol Div., Pennwalt Corp.), hyponitrites such as t-butyl hyponitrite and t-amyl hyponitrite 2-t-butylazo-2-cyano-4-methylpentane (Luazo.RTM. 70, available from same source), 4,4'-azobis(4-cyanovaleric acid), 4-t-butylazo-4-cyanovaleric acid and the like. A particularly suitable lower temperature azo initiator is 2,2'-azobis(2,4-dimethyl-4-methoxy-valeronitrile) commercially available as Vazo 33 from E. I. DuPont.

Other suitable initiators include organic peroxide compounds such as benzoyl peroxide, di-t-butyl peroxide, t-butyl peroxyacetate. A particularly suitable peroxide initiator because of its effectiveness at low temperatures is p-menthane hydroperoxide activated by FeSO.sub.4.7H.sub.2 O complexed with tetrasodium salt of ethylene diamine tetracetic acid and reduced with sodium formaldehyde sulfoxylate.

Of the above initiators, the azo compounds are presently preferred for most applications, as some peroxides appear to have a tendency to adversely affect the polymer; however, some peroxides are effective at lower temperatures than those at which most azo compounds are useful. It should be understood that compounds, such as persulfates, other than azo and peroxide compounds can be used as initiators.

Any suitable temperature can be used as for instance from -10.degree. to 100.degree. C. and in fact even temperatures above 100.degree. C. can be used if pressure is utilized to prevent vaporization of the water. Thus broadly any temperature from the freezing point to the boiling point of water under the conditions used can be employed. Preferably, however, relatively low temperatures are preferred, i.e. from 1.degree. to 10.degree. C.

Polymerization times are the same as those conventionally used in the art, generally 2 to 18 hours and preferably 2 to 6 hours, although as little as one-half hour could be used. However, attempting more rapid polymerization over a shorter period of time creates problems with removing heat. In this regard it is greatly preferred that the polymerization medium be stirred well or otherwise agitated during the polymerization.

The equipment utilized for the polymerization can simply be standard reactors such as are used for oil-in-water emulsion polymerizations.

With regard to charge order, it is preferred that the water-soluble ingredients including the monomers be mixed together and that the surfactant compositions be mixed with the oil, and thereafter the two mixtures combined. It is most preferable and effective to first mix the first surfactant composition with the oil, and then add the second surfactant composition in increasing amounts until a visibly stable emulsion results. The water is generally either distilled or deionized water.

The initiator is not generally added until after the other ingredients are all combined.

The water is generally present in an amount within the range of 50 to 200 parts by weight per 100 parts by weight of monomer(s) with about 80 to 120 parts by weight being preferred. In the case of one particular monomer combination, N-vinylpyrrolidone/2-acrylamido-2-methylpropane sulfonate, sodium salt, the preferred concentration is about 100 to 120 parts by weight of water and most preferably about 110. The continuous phase is a hydrocarbon such as that sold under the trademark "Soltrol 145" hydrocarbon. This component is generally present in an amount within the range of 60 to 120 parts by weight per 100 parts by weight of monomer(s), most preferably about 80 to 100 parts. With the specific monomer combination of vinylpyrrolidone and 2-acrylamido-2-methylpropane sulfonate, sodium salt, the preferred concentration is about 80 to 100 with about 90 parts by weight per 100 parts by weight of monomer(s) being most preferred. In the case of the preferred surfactant components, Span 80 is present in an amount of about 9 parts by weight, Tween 85 in an amount of about 11 parts by weight and Siponic E-2 in an amount of about 12 parts by weight based on 100 parts by weight of monomer(s), there being very little leeway in these matters since with regard to the Span 80 and Tween 85 they must be present in the right proportions to give the correct HLB. The second composition of the surfactant system such as the Siponic E-2 can be viewed as being present in an amount sufficient to "titrate" the system so as to give the best emulsion.

When para-menthane hydroperoxide is used as the initiator it is generally present in an amount within the range of 0.0125 to 0.05, preferably about 0.025 parts by weight per hundred parts by weight of monomer(s) with the iron compound being present in an amount within the range of about 0.000005 to 0.001, preferably about 0.00002 parts by weight per hundred parts by weight of monomer(s). The ethylene diamine tetracetic acid sodium salt with 4 molecules of water of hydration is generally present in an amount of about 0.00006 parts by weight. The reductant sodium formaldehyde sulfoxylate is generally present in the amount of 0.01 to 0.04, preferably about 0.02 parts by weight per hundred parts by weight of monomer(s). Broadly, 0.01 to 1.0 weight percent initiator based on monomers can be used.

After the polymerization has run its desired course a shortstop may be added such as "Thiostop N" which is a 40 percent sodium dimethyl dithio carbamate solution. It can be added in an amount in the range of 0.2 to 0.8, preferably about 0.4 parts by weight per 100 parts by weight of monomer(s).

With respect to the monomers, the N-vinyl lactam monomers can be depicted by the formula: ##STR1## where R.sup.3 and R.sup.4 are selected independently from the group consisting of hydrogen, methyl and ethyl and y is an integer of from 1 to 3. These monomers are generally water-soluble or water-dispersible. A more preferred class of compounds are those of the formula ##STR2## where R.sup.5 is hydrogen, methyl or ethyl. The N-vinyl lactam monomer presently most preferred is N-vinyl-2-pyrrolidone (VP).

The vinyl-containing sulfonate monomer which is meant to encompass the acid also is represented by the following formula ##STR3## where R.sup.6 is methyl, ethyl or H, preferably methyl or H, and provided further that at least one of the R.sup.6 groups on the terminal carbon of the vinyl group is H and the other is H or methyl.

M is H.sup.+, Na.sup.+, K.sup.+, Li.sup.+, Ca.sup.++ or Mg.sup.++, and z is an integer equal to the valence of M.

X is ##STR4## where n' is an integer of 1-5 preferably 1-3 and R.sup.7 is a 1-3 carbon atom alkyl group or H.

Examples of suitable vinyl-containing sulfonate compounds are: ##STR5## vinyl sulfonate, sodium salt; ##STR6## sodium 2-acrylamido-2-methylpropane sulfonate (sodium AMPS); ##STR7## styrene sulfonate, sodium salt; ##STR8## sodium vinyl toluene sulfonate; ##STR9## sodium p-vinylbenzyl sulfonate.

These are known monomers and can be produced as is known in the art. Particularly with regard to the N-sulfohydrocarbon-substituted acrylamides, they are disclosed in U.S. Pat. No. 3,679,000 assigned to the Lubrizol Corporation, the disclosure of which patent is incorporated by reference. The 2-acrylamido-2-methylpropane sulfonic acid is available from Lubrizol under the designation AMPS.

There can be used in place of, or in addition to, the vinyl containing sulfonate, an ester of the formula: ##STR10## where R' is methyl, ethyl or H, preferably methyl or H, and further provided that at least one of the R' groups on the terminal carbon is H and the other is H or methyl, and where n" is 1 to 20, i.e. compounds such as (3-sulfo-n-propyl)methacrylic ester, potassium salt.

The inverse emulsion polymerization system of this invention can be used to prepare copolymers of the N-vinyl lactam and the vinyl containing sulfonate or copolymers of either one with an unsaturated amide such as acrylamide (AM) or terpolymers, i.e. VP/AM/AMPS.

The unsaturated amide monomers referred to hereinabove have the formula ##STR11## where R" is an unsaturated radical selected from the group ethenyl (vinyl), propenyl, isopropenyl, 1-butenyl, isobutenyl(2-methyl-2-propenyl), 1-pentenyl, 1-isopentenyl(3-methyl-t-butenyl), and 1-methyl-1-butenyl. These unsaturated amides are generally water-soluble or water dispersible.

A more preferred class of unsaturated amide monomers are those of the formula ##STR12## wherein each R'" is individually selected from H and methyl. Especially suitable in addition to acrylamide are N-methylacrylamide and N,N-dimethylacrylamide (DMAM). For both the vinyl lactam and unsaturated amide the scope can be viewed functionally as including the replacement of hydrogens with hydrocarbon groups so long as the monomer remains hydrophilic. By hydrophilic is meant if the monomer were hompolymerized, the polymer would be water soluble.

Other suitable monomers useable with monomers discussed above are unsaturated organic acid monomers such as acrylic acid and methacrylic acid, and also water soluble esters of such unsaturated organic acids.

The monomer weight ratios can vary widely. Generally the copolymers will have weight ratios of 10:90 to 90:10 with the vinyl lactam/unsaturated amide copolymers generally having ratios within the range of 25:75 to 75:25, preferably 40:60 to 70:30 of lactam:amide.

Similar weight ratios can be utilized for the lactam/vinyl containing sulfonate copolymers. However, with the particular system of VP/AMPS, ratios of about 10:90 are particularly desirable.

Monomer ratios for vinyl containing sulfonate and unsaturated amide can be the same as those set out hereinabove for the N-vinyl lactam/unsaturated amide.

Terpolymer compositions can vary widely in composition but generally will contain 20 to 40 weight percent N-vinyl lactam, 10 to 20 weight percent unsaturated amide and 40 to 65 weight percent of vinyl containing sulfonate, a 30:15:55 VP:AM:NaAMPS being particularly suitable.

Screening tests were conducted with the following recipe in order to determine a suitable HLB range for the surfactant system employed in preparing the water-in-oil (inverse) emulsion of a N-vinyl pyrrolidone/acrylamide (VP/AM) (50/50) copolymer. The tests were made by preparing the emulsions (1/4 recipe in grams) at room temperature and then simply making visual observations on the stability of the emulsions as judged by their tendency to form layers on separation of the phases. The monomers were not polymerized in these screening tests.

The emulsions were prepared by dissolving the monomers in water, dissolving the surfactant in the hydrocarbon phase then vigorously mixing the two solutions in glass test tubes.

The results showed that for each of the three hydrocarbon phases employed the most stable emulsions appeared to be formed when the HLB value of the surfactant was 8.

Additional screening tests were conducted in a manner similar to that used in Example I. The inverse emulsion recipe used in these tests is shown below.

A variety of commercially available surfactants and blends thereof were screened with HLB values near 8.

A listing of the surfactants used and the corresponding HLB values are shown in the Table I below.

Suppliers are as noted previously: Triton from Rohm and Haas Co.; Siponic from Alcolac, Inc.; Span, Tween and Brij from ICI Americas, Inc. Observations on the emulsions indicated that Runs 5 and 12 were the most stable in this series of tests.

Based on the screening test results of Example II, VP/AM (50/50) copolymerization runs were made with the surfactant blends of Runs 5 and 12 but at three different ratios to obtain HLB values of 6, 7 and 8. The recipe employed in these runs is shown below. The polymerizations were conducted at 50.degree. C. with 1/4 recipe in grams per run.

Charge order: VP and AM were dissolved in water, surfactants were dissolved in the hydrocarbons and the two solutions mixed in beverage bottles which served as the polymerization reactors. Initiator solution was then charged to each bottle to start the polymerization. Table II presents further details for the runs and certain of the results obtained.

Solids measurements and Brookfield viscosities were obtained on diluted inverse emulsions produced in Runs 4-6. The results are shown in Table III.

The results in Tables II and III show that adequate polymerizations were obtained but that improvement in emulsion stability and molecular weight are still needed to be achieved with the two-component surfactant blends tested. Note in particular in Table II that the emulsions were unstable even when the surfactant blends (Siponic C-20/Siponic E-10 and Span 60/Tween 61) had an HLB of 8, which was found previously to be the optimum HLB with respect to emulsion stability.

Further runs were made to examine the effect of an added third surfactant to certain two component surfactant blends used in preparing inverse emulsions of the VP/AM (50/50) copolymer. The recipe used in these runs is shown below. The polymerizations were conducted at 50.degree. C.

Charge order (1/4 recipe in grams per run): AM, VP, H.sub.2 O, and Soltrol having surfactant dissolved therein were mixed. Each mixture was poured into a 10 oz bottle. The contents were purged 25-30 minutes with N.sub.2 and the bottle capped with a perforated crown cap having a self-sealing rubber liner. The initiator was then charged to each bottle through the cap by means of a hypodermic syringe and needle. Each bottle was then placed in a 50.degree. C. polymerization bath.

The effect of the surfactants on emulsion stability prior to initiation was observed by adding increasing amounts of Siponic E-2 to reaction mixtures already having a fixed (5 g) amount of a surfactant blend. The amount of Siponic E-2 needed to give a visibly stable emulsion was noted for each surfactant blend. In effect, a "titration" of the reaction mixture to a point of emulsion stability was performed.

The surfactant blends used and the results obtained are shown below in Tables IV and V, respectively.

Each of the surfactant blends as well as Siponic E-2 have an HLB of about 8.

Conversion data and viscosity measurements were obtained for Runs 6, 9, 13 and 17 and these results are shown in Table V.

The results show that stable emulsions which give high viscosity polymer solutions in a brine can be obtained with a three component surfactant system of the Span/Tween/Siponic E-2 type. The results with the surfactant system of Run 6 using a Triton surfactant blend were not as satisfactory.

Another series of runs were made using the same recipe and essentially the same procedures as in Example IV and the same surfactant components as in Example IV but the amounts were reduced about 50%. A further difference was the use of acetone as a solvent for the AIBN initiator rather than the monomer VP. Table VI below shows the amounts of surfactants used and the observations on emulsion stability prior to initiation.

Runs 5, 9, 12 and 16 were charged with initiator for polymerization at 50.degree. C. but each emulsion destabilized during polymerization so that no conversion data and viscosity measurements were obtained. The results of Examples IV and V indicate that at least about 25-28 phm of total surfactant is needed for stable inverse emulsion polymerization of VP/AM at 50.degree. C. with an azo initiator using a Span/Tween/Siponic E-2 surfactant blend.

Further runs were conducted using the recipe of Example IV and essentially the same procedures as in Examples IV and V with the exception that the "titrating" surfactant component Siponic E-2 was replaced by a blend of two surfactants Brij 72/Brij 78 at a wt ratio of 70.2/29.8 (HLB 8) in the Brij blend. As in Example V the AIBN initiator was charged as a solution in acetone for polymerization at 50.degree. C.

The surfactant blends employed and observations on inverse emulsion stability prior to initiation are presented in Table VII below.

Runs 6, 10, 14 and 18 were polymerized as described. The conversion results and viscosity measurements obtained are presented in Table VIII.

Runs 10 and 18 appeared to give adequate polymerization behavior and reasonably good viscosity values. However, the results in general were not as good as those of Example IV using Siponic E-2 as a surfactant component. Moreover, one less surfactant component is utilized in the runs of Example IV than the runs of this example thus reducing the complexity of the system.

In order to simplify inverse emulsion (of VP/AM copolymer) evaluation and provide a closer correlation of viscosity results with a possible end use application, it was desired to use a brine (Synthetic North Sea Water-SNSW) as a substantial portion of the aqueous phase in the preparation of the inverse emulsions of VP/AM (50/50) copolymer. Screening tests showed that a Span/Tween/Siponic E-2 surfactant blend (at about 24 phm total) could provide visibly stable emulsions at room temperature using the recipe shown in Example IV wherein 50 parts of water was replaced by 50 parts of SNSW.

Polymerization runs then were made using the recipe shown below at a temperature of 50.degree. C. using substantially the same procedures as in Examples IV--VI.

The surfactant system used in these runs are shown in Table IX with observations on emulsion stability.

Conversion data and viscosity results were not obtained for runs 1 and 2. The results obtained in runs 3-8 are shown in Table X.

The results show that reasonably good conversions and viscosity values can be obtained in the presence of a brine, SNSW, during the polymerization of VP/AM in an inverse emulsion system.

Other polymerization runs were conducted employing the recipe shown in Example IV at 50.degree. C. for about 18 hours. These runs utilized a different group of surfactants each at a total PHM of 20 as shown below in Table XI.

The Pegosperse surfactants are supplied by Glyco Chemicals, Inc.

Further runs were conducted at 50.degree. C. using the recipe of Example IV except that several different mineral oils were used instead of Soltrol 145 and a variety of surfactant systems were employed. The particular combinations of mineral oil and surfactants used as shown in Table XII.

Conversion data was obtained for Runs 8, 10, 11 and 12 but all the other runs were too severely destabilized during polymerization. The conversion data was as follows:

No viscosity measurements were made.

These results suggest that Soltrol 145 is more effective than the mineral oils in providing a stable inverse emulsion.

Parol 100, Parol 70 and oil 2257 are white mineral type oils obtained from Penreco of Butler, Pa.

Polymerization runs were conducted using the recipe shown below at 30.degree. C.

Charge Order (1/4 recipe in grams): AM and VP were dissolved in SNSW. A separate solution of the surfactant components (Span and Tween) dissolved in Soltrol 145 was prepared. The solutions were mixed thoroughly and Siponic E-2 added ("titrated") to provide a visibly stable emulsion.

The surfactants employed are shown in Table XIII below.

An additional 3 mL of SNSW was added to Run 1 which reduced the turbidity somewhat though it still was not as clear as Run 2. Runs 1 and 2 were initiated and polymerization continued for about 18 hours. The conversion data and viscosity results for these runs are shwn in Table XIV.

The results show that a VP/AM (60/40) copolymer can be prepared in an inverse emulsion system in the presence of a brine (SNSW) to high viscosity products at a reasonably good conversion rate.

Other runs were made at 30.degree. C. using a recipe very similar to that of Example X except that the brine was prepared in situ by charging a commercially available solid salts mixture with water in the preparation of the emulsions. The salts mixture (available from Lake Products Co., Inc., of Ballwin, Mo., prepared according to ASTM D-1141-52) is made to approximate that found in ocean brine composition (Synthetic Ocean Water, "SOW", salt). The recipe used is shown below:

Charge Order (1/4 recipe in grams): The SOW salt was added to the water followed by AM and VP. A separate solution of the surfactants (Span & Tween) dissolved in the Soltrol 145 was prepared. The solutions were thoroughly mixed and the Siponic E-2 added ("titrated") to provide visibly stable emulsions.

The surfactants employed are shown in Table XV below.

An additional 1 mL of SNSW was added to Run 1 to reduce turbidity. Runs 1 and 2 were initiated and polymerization continued at 30.degree. C. for about 18 hours. Conversion data and viscosity results are shown in Table XVI.

Again, the results show that a VP/AM (60/40) copolymer can be prepared in a inverse emulsion system in the presence of an in situ produced brine to high viscosity products at a reasonably good conversion rate.

Another series of runs was made at 30.degree. C. for the preparation of VP/AM (60/40) copolymers in an inverse emulsion system. In this series the effect of added NaCl was examined in contrast to the more complex brines used in Examples VII-XI. The recipe employed is shown below.

Charge order (1/4 recipe in grams): NaCl was added to the water followed by AM and VP. A separate solution of the surfactants (except Siponic E-2) in the Soltrol 145 was prepared. The solutions were thoroughly mixed and 5 g Siponic E-2 added to provide visibly stable emulsions.

The surfactant combinations used and NaCl amounts are shown in Table XVII.

Prior to initiation each bottle reactor was purged 15 minutes with nitrogen. Polymerization continued for 21 hours at 30.degree. C. then each mixture was charged with the shortstop. Conversion data and viscosity results are shown in Table XVIII.

Conversion data showed reasonably good results with the exception of Run 4. However, viscosity values, especially inherent viscosities, seem to be unexpectedly low in view of results obtained in Examples X and XI. The reason for the apparent low values is not known.

Additional runs were made using the recipe shown below with different surfactant combinations for polymerizations conducted at 30.degree. C. for about 16 hours.

Charge order (1/4 recipe in grams): A solution of AM and VP was prepared in the water component. A separate solution of surfactants (except Siponic component) in Soltrol 145 was prepared. The two solutions were thoroughly mixed and the Siponic component added to provide visibly stable emulsions. The mixtures were purged with N.sub.2 then charged with initiator and placed in the 30.degree. C. constant temperature bath.

The surfactant combinations used are shown in Table XIX.

Percent solids data and viscosity measurements are presented in Table XX below.

The results showed that copolymers of VP/AM (60/40) with good viscosity values could be obtained using the Span/Tween/Siponic surfactant combination.

Other runs were made using the recipe of Example XIII except that the Vazo 33 initiator was replaced by a redox type initiator system. Polymerization was conducted at 5.degree. C. rather than 30.degree. C. used in Example XIII.

The redox system employed p-methane hydroperoxide (PMHP) (0.06 phm), ferrous sulfate heptahydrate (Fe) (0.0003 phm), sodium formaldehyde sulfoxylate (SFS) (0.05 phm) and ethylene diamine tetraacetic acid tetra sodium salt with 4 moles of water of hydration (Questex 4SW or QWS) (0.001 phm). The PMHP "initiator" was charged as a solution in toluene (0.06 g/mL). The activator was an aqueous solution of 0.003 g Fe, 0.01 g QSW and 0.5 SFS in 100 mL water. In these (1/4 recipe in grams) runs the initiator (PMHP) was charged to the N.sub.2 purged mixture of monomers, water, Soltrol and surfactants followed by the activator. The mixtures were then allowed to polymerize at 5.degree. C. for about 16 hours. The surfactants used in these runs are shown in Table XXI below.

The solids data and viscosity results are shown in Table XXII.

Other runs were made with similar redox initiator recipes but at 50.degree. C. and with reduced total surfactant levels, e.g., about 1/2 and 1/4 the amounts used in Table XXI. However, each of these runs destabilized rather quickly and no data were obtained.

Other runs were made using a redox type initiator system for the inverse emulsion polymerization of VP/AM (60/40) at 5.degree. C. for 20 hours wherein the HLB of the surfactant system was 8. The recipe used is shown below.

Charge Order: The VP and AM were dissolved in water to form an aqueous solution 1. All of the surfactant components were dissolved in Soltrol 145 to form solution 2. The solutions 1 and 2 were thoroughly mixed then purged with N.sub.2 for 15 minutes. An aqueous solution of Fe and QSW was then charged followed by an aqueous solution of SFS. The mixtures were cooled to 5.degree. C. and held at that temperature for 30 minutes then charged with PMHP and allowed to polymerize for 20 hours. Shortstop was charged as a 40% by wt aqueous solution.

The surfactants employed in these runs are shown in Table XXIII.

The amounts of redox initiator system components and the results obtained are shown in Table XXIV.

Although several runs had poor results in terms of solids content (low conversion) and low viscosities, other runs showed that high viscosity values and solids content could be achieved with a redox initiator system and a Span/Tween/Siponic surfactant blend at HLB 8.

As a final Example, several additional runs were made using a Span 80/Tween85/Siponic E-2 surfactant system, a redox initiator system of the type used in Examples XIV and XV, and various combinations of monomers. The recipes are shown below.

Each recipe (full recipe, in grams) was mixed and inverse polymerization carried out in six corresponding runs 1-6 using essentially the same charge order and polymerization conditions described in Example XV. Viscosity and percent solids results for these runs are shown in Table XXV.

All of the runs achieved highly stable emulsions and, as can be seen from Table XXV, desirably high viscosities.

While this invention has been described in detail for the purpose of illustration it is not to be construed as limited thereby but is intended to cover all changes and modifications within the spirit and scope thereof.