CA1282542C - Emulsion polymerization - Google Patents

Abstract

ABSTRACT
Selected oxygen-containing organic polar compounds are added to an inverse emulsion polymerization process for making water soluble vinyl addition polymers to stabilize the emulsion present during inverse emulsion polymerization in a manner such that less phase separation takes place upon standing.

Description

~ 54~ 31670CA

EMULSION POLYMERIZATION
Background of the Invention This invention relakes to a water-in-oil emulsion polymerization process in which a water-soluble monomer is polymerized.
This invention further relates to improvements in processes for preparing water-soluble vinyl addition polymers by water-in-oil emulsions comprising an aqueous phase containing water-soluble monomer, an inert hydrophobic liquid, and a water-in-oil emulsifying agent. In another aspect, this invention relates to the addition of at least one stabilizing agent to emulsion polymerization processes.
Stable water-in-oil emulsions of water-soluble vinyl addition polymers are well known in the art. However, a prior art process of emulsion polymerization normally consists of a continuous oil phase (non-polar hydrocarbon), a water-in-oil emulsifying agent, a dispersed aqueous phase (including water-soluble monomer) and a free radical initiator. These emulsion polymers tend to settle over a period of time and must be redispersed by agitation.
The present invention is directed to the use of selected organic polar compounds to stabilize or to improve the emulsion present in emulsion polymerization of water-soluble monomers. By stabilization it is meant that after polymerization there is no phase separation upon standing. Thus, when the emulsion is used as a water viscosifier in water-flooding oil recovery, for example, there is no need to provide additional mixing, stirring, tumbling, ~tc. at the well site since there is no phase separation. By improvement it is meant that after polymerization the inYerse emulsion is either more homogeneous or shows ~8~54~ 31670CA

less phase separation than that without the presence of organic polar compounds. Additionally, the selected stabilizer additives of the invention can reduce the amount of the more expensive surfactants (emulsifiers) used in the polymerization process.
Accordingly, it is an object of this invention is to provide an improved inverse emulsion polymerization process.
Another object of this invention is to provide emulsion stabilizers for inverse emulsion polymerization processes.
Another object of this invention is to provide stabilizer additives for polymerization processes to facilitate handling and processing of polymeric product.
Other objects, aspects as well as the several advantages of this invention will be apparent to those skilled in the art upon reading the specification and the appended claims.
Summary of the Invention In accordance with the invention, it has been found that the use of selected oxygen-containing organic compounds stabilize the emulsion present during and after inverse emulsion polymerization of water-soluble monomers.
More specifically, according to the invention, it has been found that oxygen-containing organic compounds selected from amides, alcohols, ketones, esters, and ethers are effective in stabilizing emulsion during inverse emulsion polymerization of water soluble monomers to produce water-soluble vinyl addition polymers.
In accordance with specific embodiments of the invention it has been found that N-methyl-2-pyrrolidinone, acetone, tert-butyl alcohol, n-amyl alcohol and n-decyl alcohol are all effective emulsion stabilizers in inverse emulsion processes.
Description of Specific Embodiments As noted above, the invention is directed to improving a water-in-oil emulsion polymerization processes especially wherein the stability of the emulsion is significantly improved by the addition of certain oxygen-containing organic polar compounds to the polymerization.
For example, the addition of about .03 weight percent of N~
(N-methyl-2-pyrrolidinone) to a polymerization recipe based on i~82542 31670CA

acrylamide~ hydrocarbon, water, surfactant and initiator results in a stable emulsion during and after polymerization with no phase separation compared to phase separation when NMP is not present. The invention is also useful for other monomers and other oxygen-containing emulsion stabilizers such as acetone, tetrahydrofuron, methanol, tert-butyl alcohol, n-amyl alcohol, n-decyl alcohol, and the like.
Emulsion Stabilizers The inverse emulsion stabilizers useful in this invention are four types of oxygen-containing organic compounds which are generically N-alkyl amides, alcohols, ketones, esters and ethers.
The liquid N-alkyl amides are those materials represented by the formulas 15R5 - C = C \
\ O
N-Rl OR ll R6 - C = C - Rg R7 Rs (I) (II) where Rl and R2 can be any linear or branched alkyl group having 1 to 14 carbon atoms, preferably 3 to 12 carbon atoms; R3 can be hydrogen or any alkyl radical having 1-16 carbon atoms; and R4, R5, R6, R7, R8 and Rg can be hydrogen or any linear or branched alkyl group having 1 to 6 carbon atoms.
Exemplary amides are for example but not limited to N-methylformamide N,N-dimethylformamide N-methyl-N-dodecylformamide N-n-propyl-N-butylformamide N,N-dimethylacetamide N,N-dimethylpropionamide ~ ~2~4Z 31670CA

N,N-dimethylcaproamide N-methyl-2-pyrrolidinone N-hexyl-2-pyrrolidinone N-dodecyl-2-pyrrolidinone N-methyl-3,4-dimethyl-2-pyrrolidinone, and the like, and mixtures thereof.

The alcohols useful in this invention are those materials represented by the formula RlOH

where Rl is as previously defined.
Exemplary alcohols are for example but not limited to methyl alcohol ethyl alcohol isopropyl alcohol n-butyl alcohol tert-butyl alcohol isoamyl alcohol decyl alcohol dodecyl alcohol tetradecyl alcohol, and the like, a~d mixtures thereof The ketones useful herein are those materials represented by the formula Rl-C-R2 ll o ~825~2 31670C~

where Rl and R2 are as previously defined.
Exemplary ketones are for example but not limited to dimethyl ketone (acetone~
methylethyl ketone methylisobutyl ketone hexyldodecyl ketone and the like, and mixtures thereof.
The ethers useful herein are those materials represented by the formula Rl-O-R2 where Rl and R2 are as previously described.
Exemplary ethers are for example but not limited to dimethyl ether diethyl ether di(tetradecyl) ether, and the like, and mixtures thereof. In addition some cyclic ethers can be used such as tetrahydrofuran, 2,5-dimethyl tetrahydrofuran, and the like.
The esters that are useful in the invention include alkyl or aromatic esters of linear or cyclic carboxylic acids having from 1 to about 20 carbon atoms. Examples include methyl formate, ethyl octonate, methyl anisa~e, ethyl benzoate, diethyl carbonate, ethylene carbonate, diphenyl carbonate, and the like and mixtures thereof.
Broadly~ the amount of stabilizer needed can be any amount which produces a stable emulsion. A further requirement is that the stabilizer be soluble in either the water or hydrocarbon phase of the emulsion or both. The amount of stabilizer needed to provide stable emulsions can be about 0.01 to about 25 weight percent, preferably about 0.1 to 10 weight percent based on the total weight of the complete emulsion composition.

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Water-Soluble Monomers All known water-soluble unsaturated monomers can be polymeriz~d by inverse emulsion polymerization process of this invention. Such monomers include acrylamide, methacrylamide, acrylic acid, methacrylic acid, vinylbenzyl trimethylammonium chloride, alkali metal and ammonium salts of 2-sulfoethylacrylate, 2-amineothyl methacrylate hydrochloride, alkali metal and ammonium salts of vinylbenzyl sulfonate, and the like, and mix*ures thereof.
Addi~ional illustrative examples of monomers useful in this invention include 2-acrylamido 2-methyl-propanesul~onic acid, and the water-soluble salts of acrylic and methacrylic acids such as their ammonium and alkali metal salts.
The ab~ve described moncmers and water comprise the aqueous phase of the water-in-oil emulsion.
Oil-Phase Materials The oil phase of the emulsion comprises an inert hydrophobic liquid and a water-in-oil emulsifying agent (surfactant). Any inert hydrophobic liquid can be used including, for example, aliphatic and aromatic hydrocarbons and halocarbons such as toluene, xylene, dichlorobenzene, perchlorethylene, hexane, heptane, isooctane, kerosene, mineral oil and Soltro ~, a high purity isoparaffinic material sold by Phillips Petroleum Co. Iikewise, any conventional water-in-oil emulsifying agent can be used such as hexadecyl sodium phthalate, sorbitan monooleate, sorbitan monostearate, mono- and diglycerides, polyethoxylated sorbitol ~axaoleate, cetyl or stearyl sodium phthalate, metal soaps or combinations thereof. Preferred emulsifying agents (surfactants) æ e sorbitan monooleate and a blend of polyethoxylated sorbitol hexaoleate and mono- and diglycerides~ These emNlsifying agents constitute abou~ 0.1% to about 10%, preferably about 1% to about 5% by 3~ weight of the emulsion.

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Polymerization Initiators ~Catalysts) Polymerization can be carried out using high energy irradiation, e.g. gamma irradiation from co60, or high energy electrons from a Van de Graff accelerator, etc., or ultraviolet irradiation. Free radical initiation is presently the preferred method of polymerization.
The initiator can dissolve in either the water phase or oil phase depending upon its solubility characteristics. The preferred initiators are those dissolving in the oil phase. Exemplary of such initiators are benzoyl peroxide, lauryl peroxide azobisisobutyronitrile (AIBN), 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN), tertiary butyl hyponitrite, and the like. The amount of initiator used can be in amounts ranging from about 1.0 to about 10,000 parts per million (ppm) based on the weight of the monomers.
Monomer-Hydrocarbon-Water Ratios Proportions between 99 and 5 percent monomer corresponding to 1 to 95 percent water are used depending upon the monomer and the temperature of polymerization. The ratio of aqueous phase to oil phase is also widely variable, advantageously between 30 and 70 parts of the former to between 70 and 30 parts of the latter by weight. An aqueous phase to oil phase ratio of about 60 to about 40 is preferred.
Polymerization Conditions The reaction time is widely variable depending upon the catalyst or initiation system and ranges generally between about lO
minutes and two hours at temperatures between about 20C and 100C.
EXAMPLE I
This example illustrates the effectiveness of certain oxygen-containing polar organic compounds in stabilizing an inverse emulsion polymerization process whereby the water-soluble monomer is sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS~). To a lO-ounce polymerization bottle was added in the order listed the following ingredients: 25 grams of an isoparaf~inic solvent (Soltrol~ 145), 5 milliliters of a surfactant sorbitan monooleate (Span~ 80 from ICI), 5 milliliters N-methyl-2-pyrrolidinone, lO grams distilled water, and 40 grams of a 50 weight percent aqueous solution of NaAMPS. The bottle was capped, purged with nitrogen or argon followed by the addition of 0.025 ~ 32S4~ 31670CA

grams of tertiary butyl hyponitrite catalyst (12 weight percent based on the moncmer) dissolvPd in 0.5 milliliters of toluene. The total solids content at this point was estimated to be 24.8 weight percent. The bottle and contents were placed in a mechanical tumbler which was imm~rsed in a constant temperature water bath (30) and tu~bled for 24 hours. The bcttle contents were then removed and allowed to stand at ambient room temperature for 4 to 24 hours during which time any phase separation was noted. With N-methyl-2-pyrrolidinone as the stabilizer additive, relatively less phase separation was observed after 24 hours as ccmpared to the control run.
A portion of the mverse em~lsion was removed and diluted with a synthetic North Sea water (SNSW) to a 0.25 weight percent emulsion mixture. The SNSW was comprised of 23,8330 grams NaCl, 10.7735 grams for a total weight of 40.7430 grams which was then diluted to 1 liter with distilled water. The bulk viscosity of the diluted 0.25 weight percent inverse emNlsion mixture was m asured at ambient room temperature (-25C) using a Erookfield Visccmete ~, LVT mcdel with UL spindle at 12 rpm and found to be 2.05 centipoise (cps).
The above descri~ed procedure was repeated but with various different type emNlsion stabilizer additives. These results along with the previous N-methyl-2-pyrrolidinone results are listed in Table 1 wherein it was shcwn that not all oxygen-containing liquid organic ccmpcunds are satisfactory emulsion stabilizers.

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TABLE I
Inverse Emulsion Polymerization Stabilization Recipe: 25 g Isoparaffinic Solvent (Soltrol~ 145) 5.35 g Surfactant-Sorbitan Monooleate 5 mL Emulsion Stabilizer Additive 10 g Water 40 g 50 Wt. % Aq. Sodium 2-Acrylamido-2-methylpropanesulfonate (NaAMPS~) .5 mL t-C4Hyponitrite in Toluene lO Run Visc., No. Stabilizer Additive,(g) Results cps Controls:
1 None ~ inch top phase separation 3.75 2 Dimethylsulfoxide,(5-5) l/8 ' 3.80 3 Hexamethylphosphoramide, Unstable. " " "
(5.2) Invention:

4 N-methyl-2-Pyrrolidinone, Stable, no phase separation 2.05 (5.2) Acetone,(4.4) Stable, " " " 3.72 The data indicate that dimethylsulfoxide (Run 2) and hexamethylphosphoramide (Run 3) do not function as emulsion stabilizers in an inverse water-in-oil emulsion polymerization of sodium 2-acrylamido-2-methylpropanesulfonate. The data further indicate that N-methyl-2-pyrrolidinone (Run 4) and acetone (Run 5~ are effective as emulsion stabilizers in an inverse emulsion system.
EXAMPLE II
This example illustrates the effectiveness of certain oxygen-containing polar organic compounds in stabilizing an inverse emulsion polymerization process whereby the water-soluble monomer is acrylamide. The polymerization process was essentially as that described in Example I except with the following charge: 30 grams toluene, 5 milliliters of sorbitan monooleate surfactant ~Span~ 80), 5 milliliters of inverse emulsion stabilizer additive, 46 grams of water, 20 grams acrylamide and 0.025 grams of azobisisobutyronitrile catalyst. The 1~8~ 31670CA

results from this inverse emulsion polymerization are listed in Table II
which again shows that only certain type oxygen-containing organic compounds are useful preventing phase separation during an inverse emulsion polymerization process.
TABLE II
Inverse Emulsion Polymerization Stabilization Recipe: 30 g Toluene Solvent 5.35 g Sorbitan Monooleate 5 mL Emulsion Stabilizer Additive 46 g Water 20 g Acrylamide .5 mL Azobisisobutyronile in Toluene Run Visc., No. S-tabilizer Additive,(g) Results cps Control:
1 None,(0) ~ inch top phase separation 2.0 2 DimethylsulfoxidP, ~ " " " " 2.5 (5-5) Invention:
20 3 N-Methyl-2-Pyrrolidinone Stable, but too thick to (5.2) stir 4 Tert-Butyl Alcohol, (3.9) Stable, very thick 1.2 n-Amyl Alcohol,(4.1) " " " 1.2 6 n-Decyl Alcohol,(4.1) Stable, but too thick to stir The data indicate dimethylsulfoxide (run 2) does function as a stabilizer to lower phase separation. The control (run 1) showed some coagulam. In contrast, the addition of dimethylsulfoxide (run 2) showed no coagulam. Interestingly, N-mPthyl-2-pyrrolidinone provided stabilization for the acrylamide-based inverse emulsion polymerization process in that no phase separation resulted but the system was thick and could not be agitated easily. The data further indicate that aliphatic alcohols (runs 4 and 5) likewise prevent phase separation. The presence of the alcohols appears to gi~e thick solutions but viscosity measurements still remain low.
EXAMPLE III
To illustrate the improved performance of w/o emulsions of water-soluble polymers by using polar organic compounds, the procedure of Example I was repeated except with the following change as listed in Table III.
TABLE III
Inverse Emulsion Polymerization Stabilization Recipe: 30g Isoparaffinic Solvent (Soltrol 145) 3.2 g Surfactant-Sorbitan Monooleate 2 mL Organic polar compound 20 g 50 weight percent aqueous NaAMPS
0.1 g AIBN
50C for 20 hours.
0.1% I.V.
Run No. Organic Polar Compound, (g) Results in SOW
1 None (Control) translucent, 2 lig. 4.4 emulsion phases can be re-dispersed 2 CH3 (1-6 gm) transparent, 2 lig 3.7 emulsion phases can easily be re-dispersed into stable emulsion 3 Acetone (1.7 gm) translucent, 2 lig 4.8 emulsion phases can easily be reAdispersed 4 THF (1.8 gm) translucent, 2 lig. 3.6 emulsion phases can be re-dispersed The data shows that methyl alcohol (Run 2) would improve the emulsion from a translucent (Control Run) to a transparent emulsion.
The data also shows that acetone (Run 3) and THF (Run 4) can slightly improve the stability of the emulsion.

Claims (13)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In inverse water-in-oil polymerization of water soluble ethylenically unsaturated monomers to produce water soluble addition polymers, the improvement for stabilizing the inverse emulsion which comprises adding to the polymerization an emulsion stabilizing amount of at least one oxygen containing organic polar compound stabilizer which is soluble in water and/or oil phase and is selected from N-alkyl amides, ketones, esters and ethers said ethers represented by the formula R1-0-R2 wherein R1 and R2 can be any linear or branched alkyl group having 1 to 14 carbon atoms, or R1 and R2 can be joined together to form a cyclic ether.

2. A process according to claim 1 wherein the stabilizing amount ranges from about 0.01 to about 25 percent of the complete emulsion composition.

3. A process according to claim 1 wherein the polymerization is catalysed with a free radical initiator.

4. A process according to claim 3 wherein said free radical initiator is oil soluble.

5. A process according to claim 1 wherein said stabilizer compound is N-alkyl. amide.

6. A process according to claim 5 wherein said amide is N-methyl-2-pyrrolidinone and said monomer is sodium 2-acrylamido-2-methylpropanesulfonate.

7. A process according to claim 1 wherein said stabilizer compound is a ketone.

8. A process according to claim 7 wherein said ketone is acetone and said monomer is 2-acrylamido-2-methylpropanesulfonate.

9. A process according to claim 1 wherein said stabilizer compound is an N-alkyl amide and said monomer is acrylamide.

10. A process according to claim 9 wherein said amide is N-methyl-2-pyrrolidinone.

11. A process according to claim 1 wherein said stabilizer is an ether.

12. A process according to claim 11 wherein R1 and R2 are joined together to form a tetrahydrofuran ring which may be substituted by one or more alkyl substituents.

13. A process according to claim 12 wherein said ether is tetrahydrofuran and said monomer is 2-acrylamido-2-methylpropanesulfonate.