A MICELLAR PROCESS FOR THE FORMATION OF ACRYLAMIDE-ALKYL ACRYLAMIDE COPOLYMERS

Abstract: The present invention relates to a free radical copolymeri­ zation process for forming copolymers of acrylamide/alkyl ac­ rylamide having the formula: wherein R₁ is an alkyl or cycloalkyl group having 6 to 22 carbon atoms, R₂ is the same or different alkyl group as R₁ or hydro­ gen, x is 90.0 to 99.9 mole %, and y is 0.1 to 10.0 mole %.

Description: The present invention relates to unique and novel copolymers of acrylamide and alkyl acrylamide and the process for forming these copolymers, wherein these copolymers are characterized by the formula: EMI1.1 wherein R1 is alkyl, preferably a C6 to C22 alkyl, or cycloalkyl group, more preferably C6 to C20, and most preferably C6 to C18; R2 is the same or different alkyl group as R1, or hydrogen; x is preferably 90.0 to 99.9 mole %, more preferably 95.0 to 99.8; and most preferably 97.0 to 99.5; y is preferably 0.1 to 10.0, more preferably 0.2 to 5.0, and most preferably 0.5 to 3.0. The present copolymers of this invention are excellent viscosifiers for the modification of the viscosity of aqueous and saline solutions as exemplified by the preferred embodiments of the present invention. The homogeneous micellar copolymerization process of the present invention comprises the steps of forming a mixture of dodecyl sulfate, acrylamide and alkyl acrylamide under a nitrogen atmosphere; adding deoxygenated water to said mixture to form a reaction solution; heating said reaction solution to at least SOOC; adding a free radical initiator to said reaction solution to initiate the copolymerization of the acrylamide monomer and the alkyl acrylamide monomer; polymerizing the monomers at a sufficient temperature and for a suffi cient time to form the water soluble copolymer of acrylamide/alkyl acrylamide; and recovering the water soluble copolymer from the reaction solution. The drawings illustrate a plot of viscosity versus concentration for an acrylamide/octyl acrylamide copolymer. The viscosifying agents for aqueous and saline solutions of the present invention are copolymers formed by a unique and novel microemulsion, homogeneous, free radical, micellar copolymerization wherein the water soluble copolymers are characterized by the formula: EMI2.1 wherein R1 is alkyl, preferably a C6 to C22 alkyl or cycloalkyl group, more preferably C6 to C20 and most preferably C6 to C18, R2 is the same or different alkyl group as R11or hydrogen. Typical, but nonlimiting examples of preferred alkyl groups are hexyl, octyl, decyl, dodecyl and steryl groups. X is preferably 90.0 to 99.9 mole %, more preferably 95.0 to 99.8 mole %, and most preferably 97.0 to 99.5 mole % and y is preferably 0.1 to 10.0 mole %, more preferably 0.2 to 5.0 mole % and most preferably 0.5 to 3.0 mole %. The viscosities of aqueous solutions of these polymers were measured by means of a ContravesTM low shear viscometer model LS30 using a No. 1 cup and No. 1 bob. Temperatures were controlled to +0.10C, and measurements were made at a rotational speed that gave a shear rate of 1.28 s-l. The homogeneous micellar copolymerization process of the present invention comprises the steps of forming a mixture of sodium dodecyl sulfate or other suitable surfactants, acrylamide and alkyl acrylamide under a nitrogen atmosphere; adding deoxygenated water to said mixture to form a reaction solution; adding a free radical initiator to said reaction solution to initiate the copolymerization of the acrylamide monomer and the alkyl acrylamide monomer; polymerizing the monomers at a sufficient temperature and for a sufficient time to form the water soluble copolymer of acrylamide/alkyl acrylamide; and recovering the water soluble copolymer from the reaction solution. Suitable alkyl or N,N-dialkyl acrylamide monomers useful in the preparation of the copolymers of the present invention are acrylamides having alkyl groups having 6 to 22 carbon atoms, more preferably 7 to 20; and most preferably 8 to 18. Typical, but non-limiting examples are hexyl acrylamide, octyl acrylamide, decyl acrylamide, dodecyl acrylamide, steryl acrylamide and N,N-dioctyl acrylamide. Suitable free radical initiators for the present free radical-copolymerization process are potassium persulfate; sodium thiosulfate, potassium persulfate mixture, and benzoyl peroxide and other common free radical initiators. The conceittration of the free radical initiator is about 0.01 to about 0.50 grams per 100 grams of acrylamide monomer and alkyl acrylamide-monomer. Polymerization of the acrylamide monomer and alkyl acrylamide monomer is effected at a temperature preferably of 0 to 700C, more preferably at 35 to 650C, and most preferably at 45 to 550C for a period of 1 to 48 hours, more preferably at 2 to 36, and most preferably at 4 to 24. A suitable method for recovery of the formed copolymer from the reaction solution comprises precipitation into acetone. The following examples illustrate the present invention. EXAMPLE 1 Preparation of N-(n-octyl acrylamide) A 500 ml., 4 necked round bottom flask was equipped with a condenser, thermometer, N2 inlet, magnetic stir bar and dropping funnel. After purging with N2, the n-octylamine, 14.35 g. (0.11 mol.) and triethylamine, 12.35 g. (0.41 mol.) were mixed with 50 ml. of toluene and added to the flask. The acryloyl chloride, 10.0 g. (0.11 mol.) was dissolved in 50 ml. of toluene and added to the dropping funnel. The reaction is exothermic so the temperature was controlled via an ice bath. The acryloyl chloride was added dropwise so that the contents of the flask stayed below 400C. The resulting slurry was stirred for an additional hour and then filtered to remove the triethylamine hydrochloride. The filtrate was stripped in a rotary evaporator (removal of toluene) . The resulting oil was taken up into 240 ml. of acetone and then cooled to -700C in a dry ice bath. The monomer crystals were filtered on a coarse filter under N2 and then vacuum dried at room temperature for one day. A yield of 14.3 g. (¯70%) of white crystals was obtained. A melting range of 36 to 370C was observed. The monomer appeared to soften on extended storage at room temperature. EXAMPLE 2 Preparation of N-(n-Dodecyl Acrylamide) Same procedure as in Example 1 except 20.36 g. (0.11 mol.) of n-dodecylamine was substituted for the n-octylamine. EXAMPLE 3 Micellar Copolymerization of 99.25/0.75 Mole % Acrylamide/Octyl Acrylamide A one liter flask was equipped with an elc- tric stirrer, reflux condenser, thermometer and inert gas inlet and outlet. The flask was flushed with nitrogen for one half hour. Then 15.85 g. of sodium dodecyl sulfate (Polysciences), 14.76 g. of acrylamide (twice recrystallized) and 0.288 g. of octyl acrylamide and then 470.7 g. of water that was deaerated with bubbling N2 was added to the reaction flask. After a few minutes, a homogeneous, water-clear mixture resulted. It was then heated to 500C and 0.01 g. of potassium persulfate initiator was added. After 24 hours of stirring at this temperature, the mixture became very viscous, but it remained homogeneous and transparent. It was then cooled to room temperature, removed from the reaction vessel and precipitated by the addition of acetone. The polymer was then vacuum dried at room temperature for four days. The result was 9.2 g of a pure white friable solid. EXAMPLE 4 Acrylamide/Octyl Acrylamide//99/1 Mole Percent in Tween 60 Microemulsion To carry out the polymerization, 25g of the surfactant mixture comprising 15.85g of Tween-60, 8.15g of N-pentanol and l.0g of hexadecane (ex water) was prepared and 0.5g of octyl acrylamide was added. A clear mixture resulted. This was placed in the reactor and then 460 ml of deaerated water was added under N2 and 14.69g of acrylamide was added. After mixing, the solution was still water-clear, comparable in clarity to the Tween-60 microemulsion itself without added comonomers. The initiator, consisting of potassium persulfate (O.Olg) was added when the temperature reached 500C. The temperature was maintained for 24 hours. The resulting mixture became slightly hazy and slightly foamy. The polymer was recovered by precipitation into acetone and it was redissolved into water. EXAMPLE 5 Solution Properties The polymer (0.3 g.) prepared as in Example 4 was dissolved into 100 ml. of 2% NaCl solution overnight with rather vigorous agitation. This solution was used as a stock to be diluted with 2% NaCl and viscosities at a shear rate of 1.28 s-l, 250C were measured by means of a ContravesTM LS-30 viscometer. EMI7.1 The data are shown inigure . For comparison, the viscosity of two other polymers in 2% Nazi, as a EMI7.2 function of concentration, are also shown in/Figure The acrylamide/octyl acrylamide copolymer of Example 3 was prepared according to a the micellar process. The results for a sample of Dow Pusher 700TM, a commercially available, partially hydrolyzed polyacrylamide, are also shown in the Figure. Above about 2000 ppm, the micellar copolymerized material has a superior thickening efficiency. The exceedingly sharp upsweep in the viscosity of the micellar copolymerized material is probably due to the increased interchain interactions. The polymer has a measured intrinsic viscosity of [ n ] = 6 + 1 dl g'l. Therefore, the threshold overlap concentration is about 0.16 g/dl, so the sharp upsweep is about where it is expected to be. At low concentrations (below the threshold overlap concentration) , of course, the PusherTM material is superior because of its chain expansion due to the polyelectrolyte effect and perhaps because it is a higher molecular weight material. The polymers produced by this method also have a higher value for the Huggins' parameter, kh defined by the equation: EMI8.1 where TI and flo are the viscosity of the solution and solvent respectively, c is the polymer concentration in g/ml. and [11] is the intrinsic viscosity. A high value of kh means that the viscosity increases more sharply with concentration. Table 1 shows values obtained for these parameters, where the linear fits to five data points where the viscosity ranged from 1.2 to 2.0 cP were used. Table I shows that all of the values of kh for the Huggins' parameter were larger for the copolymers than for the homopolymers. The values obtained for homopolymers is usually about 0.3 to 0.7, so these copolymers are significantly higher. This shows that viscosities of solutions at finite concentrations can indeed be enhanced by a hydrophobic interchain interaction. TABLE 1 Intrinsic Viscosities and Huggins' Parameters for Am/CgAm Copolymers % C8Am [n ] - kh 0.00 3.3 + 0.3 dl/g 0.68 + 0.1 0.25 4.2 + 0.3 2.4 + 0.2 0.50 4.0 + 0.2 1.5 + 0.1 0.75 6.6 + 1.2 2.1 + 0.5

Claims: CLAIMS: 1. A homogeneous micellar free radical copolymerization process for the formation of a copolymer of acrylamide/alkyl or N,N-dialkyl acrylamide which comprises the steps of: (a) forming a mixture of sodium dodecyl sulfate or other suitable surfactant, acrylamide monomer and alkyl acrylamide monomer under a nitrogen atmosphere; (b) adding deoxygenated water to said mixture to form a reaction solution; (c) adding free radical initiator to said reaction solution to initiate polymerization of said acrylamide monomer and said alkyl acrylamide'monomer; and (d) polymerizing said acrylamide monomer and said alkyl acrylamide monomer at a sufficient temperature and for a sufficient period of time to form said copolymer of acrylamide/alkyl acrylamide. 2. A process according to claim 1 wherein said copolymer is water soluble. 3. A process according to claim 1 or 2 further including recovering said copolymer from said reaction solution. 4. A process according to claim, 2 or 3 wherein said copolymer has the formula: EMI10.1 wherein R1 is a C6 to C22 alkyl or cycloalkyl group, R2 is the same or different alkyl group as R1 or hydrogen, x is 90.0 to 99.9 mole %, and y is 0.1 to 10.0 mole %. 5. A process according to claim 4 wherein R1 is selected from hexyl, octyl, decyl, dodecyl or steryl groups, and R2 is selected from the same group as for R1 or is hydrogen. 6. A process according to any one of the preceding claims wherein said free radical initiator is selected from potassium persulfate; sodium thiosulfate, potassium persulfate mixture; and benzoylperoxide or other common free radical initiators. 7. A process according to any one of the preceding claims wherein said polymerization is carried out at about 0 to about 700C for about 1 to about 48 hours. 8. A process according to any one of the preceding claims wherein the concentration of said acrylamide monomer and said alkylacrylamide monomer in said reaction solution is about 1.0 to about 50.0 grams of said acrylamide monomer and said alkyl acrylamide monomer per 100 grams of water. 9. A copolymer having the formula: EMI11.1 wherein R1 is an alkyl or cycloalkyl group having 6 to 22 carbon atoms, R2 is the same or different alkyl group as R1, or hydrogen, x is 90.0 to 99.9 mole %, and y is 0.1 to 10.0 mole %. 10. A copolymer of acrylamide/dodecylacrylamide.

Inventors: BOCK, JAN, SIANO, DONALD BRUCE, TURNER, SAM RICHARD
Applicants: EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1983
Main classification: C08F220
IPC codes: C09K8, C08F220