A PROCESS FOR FORMING ACRYLAMIDE-ALKYL ACRYLAMIDE COPOLYMERS

Abstract: The present invention relates to a free radical micro-­ emulsion copolymerization process for forming copolymers of acrylamide/alkyl acrylamide having the formula: wherein R₁ is an alkyl or cycloalkyl group having 6 to 22 carbon atoms, R₂ is the same of different alkyl group as R₁, or hydrogen, 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 straight chained or branched 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 0.2 to 3.0. The instant 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 instant invention. The instant polymers are also excellent drag reduction agents for aqueous and saline solutions. The 1process for forming these unique and novel copolymers of tbe:instant invention comprises the steps forming a surfactant solution of a surfactant such as Tween 60, an alcohol such as n-pentanol and an alkane such as hexadecane, adding alkyl acrylamide monomer to the surfactant solution; adding water to the surfactant solution with alkyl acrylamide; adding with mixing acrylamide to the mixture of surfactant solution, alkyl acrylamide and water to form the reaction solution, adding an initiator to the reaction solution maintained at 50 C to initiate polymerization; polymerizing said reaction solution for a sufficient time to effect polymerization; and recovering the formed copolymer of acrylamide and alkyl acrylamide. In the drawings: Figure 1 illustrates - a plot of reduced viscosity versus concentration for acrylamide/dodecyl acrylamide copolymers. Figure 2 illustrates a plot of reduced viscosity versus concentration of acrylamide/dodecyl acrylamide copolymers and the effect of salt thereupon. Figure 3 illustrates a plot of reduced viscosity versus concentration for acrylamide/octyl acrylamide. Figure 4 illustrates a plot of reduced viscosity versus concentration of acrylamide/octyl acrylamide copolymers and the effect of salt thereupon. The viscosifying agents for aqueous and saline solutions of the present invention are copolymers formed by a unique and novel microemulsion, free radical copolymerization wherein the water soluble copolymers are characterized by the formula: EMI2.1 wherein R1 is alkyl, preferably a C6 to C22 straight chained or branched 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. Typical, but nonlimiting examples of preferred alkyl groups are hexyl, octyl, decyl, dodecyl and stearyl 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 0.2 to 3.0 mole %. The viscosities of these solutions 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 1,28so1. The concentration dependence of the solutions are plotted in Figure 1 for different mole fractions of dodecyl acrylamide. As the mole fraction of hydrophobic dodecyl acrylamide is increased in the copolymers, the specific viscosity per unit mass of polymer also increases. An important feature demonstrated by these data is that the intercepts at zero concentration are independent of the mole fraction of dodecyl acrylamide. This intercept is the intrinsic viscosity, defined as: EMI3.1 where o is the viscosity of the solvent, n is the measured viscosity of the solution with a concentration of polymer c. This intrinsic viscosity is related to the molecular parameters for a homopolymer by: Vh [n] = 2.5 NA Mw where NA is the Avagadro number, Mw is the polymer molecular weight and Vh is the hydrodynamic volume. For copolymers with a repeating backbone unit, the hydrodynamic volume is given by: vh = 4 # # R 3 where RG is the radius of gyration of the polymer, and 5 is a dimensionless constant with a theoretical value of 0.875 for polymer having a random chain conformation. The radius of gyration is given by: 0.6 RG = ## where ss is an effective bond length and v is the degree of polymerization. The molecular weight of a copolymer with a mole fraction l-y of acrylamide (Mw = 71) and dodecyl acrylamide (Mw = 239) is given by: Mw = [(l-y) 71 + 239y]# or Mw = (71 + 168y)v so EMI4.1 This formula permits one to compare intrinsic viscosities for acrylamide/dodecyl acrylamide copolymers in a simple way. For example, the copolymer with x = 0.98 can be compared with the homopolymer, which has x = 1.0: EMI4.2 Thus, if the degree of polymerization for the two polymers are the same, their intrinsic viscosities should differ by only one percent. Conversely, if the intrinsic viscosities of the two polymers differ by only a few percent, then we may infer that their degrees of polymerization are nearly the same. Figure 1 therefore shows that the degree of polymerization of the copolymers and homopolymer are very nearly all equal, and that introduction of the dodecyl acrylamide produces a beneficial enhancement in viscosity. The copolymers of the acrylamide and the alkyl acrylamides are formed by the free radical copolymerization process which comprises the steps forming a surfactant solution of a surfactant, an alcohol and an alkane solvent adding alkyl acrylamide monomer to the surfactant solution adding deaerated water under N2 to the surfactant solution and then adding acrylamide monomer to the mixture of the surfactant solution and water; mixing the mixture until a homogeneous reaction solution has been achieved; adding -sufficient free ¯ radical initiator to the reaction solution at a temperature of at least 500C; polymerizing the acrylamide monomer and alkyl acrylamide for a sufficient period of time at a sufficient temperature to effect polymerization; and recovering the formed copolymer from the reaction solution. Suitable surfactants used in forming the surfactant solution are Tween-60 (ICI Americas), sodium oleate, sodium laurate, ethylene oxide, propylene oxide copolymers (Pluronics), and olyelhexylate. Tween-60 is a polyoxyethylene-20-Sorbitan Monostearate having the formula: EMI6.1 Polyoxyethylene 20-Sorbitan Monostearate wherein u | + v + y + z = 20. Suitable alcohols used in forming the surfactant solution are n-pentanol, isopropyl alcohol. Suitable N-alkane solvents used are octane, hexadecane, dodecane, decane, and hexane. The concentration of alcohol is 20 to 40 wt.% of the surfactant solution, the concentration of the n-alkane solvent is 1 to 10 wt.t of the surfactant solution, and the concentration of the surfactant is 30 to 80 wt.%. The selection of the proper surfactant to use in the polymerization reaction is dependent upon the alcohol and N-alkane solvent used in the polymerization reaction. Suitable alkyl or N,N-dialkyl acrylamide monomers useful in the preparation of the copolymers of the present invention are alkyl acrylamides having an alkyl group having 6 to 22 carbon atoms, more preferably 7 to 20; and most preferably 8 to 18. Typical, but nonlimiting 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; benzoylperoxide and other common free radical initiators. The concentration of the free radical initiator is 0.01 to 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 of 25 to 900C, more preferably at 30 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 9. (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. (cry70%) of white crystals was obtained. A melting range of 36 to 370C was observed. The monbmer 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 Acrylamide/Dodecyl Acrylamide//98/2 in Tween-60 Microemulsion This polymerization was carried out in the same manner as Example 3, except that l.Og (2 mole %) of dodecyl acrylamide was used to make a somewhat more hydrophobic polymer. The reaction product was similar in appearance to Example 2 and had a similar low microgel content. The reaction product did not phase separate and was macroscopically homogeneous. However, when the polymer was separated from the surfactant by repeated acetone precipitation, the product was not completely soluble in water. Approximately 40% of a 1% solution in water contained in a test-tube formed a swollen, turbid gel in the bottom of the tube. A sample of the same polymer added to the Tween-60 microemulsion at the same concentration, however, formed a uniform, slightly turbid phase. EXAMPLE 4 Acrylamide/Dodecyl 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.lug of n-pentanol and l.0g of hexadecane (ex water) was prepared and 0.5g of dodecyl 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 (0.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. A much lower level of microgel was found to be present compared to that found in Example 3. A Comparison of Copolymers from Examples 3 and 4 A feature which distinguishes the microemulsion polymerization technique is the relative uniformity of the resulting product. Microgel formation is one indication of the uniformity of the product solution. Relative amounts of microgel were qualitively assessed by determining the volumes of polymer solutions (with a concentration of 0.5 wt.%) that could pass through a NucleoporeTM polycarbonate filter which was 13 mm in diameter and had a pore size of 5y m. The water-polymerized copolymer plugged the filter after only 6 cm3 of solution passed through it, while the Tween 60 microemulsion polymerized copolymer was able to pass 28 cm3 of water before plugging. Thus, the microemulsion polymerization technique as taught in this memorandum provides a product that produces a more uniform polymer solution. One method for ascertaining the incorporation of hydrophobic groups in a water soluble polymer structure involves solubilization of a hydrophobic material which is normally insoluble in the aqueous phase. The solubilization properties of the two copolymers were compared by measuring the saturation uptake of an oil soluble dye into a 0.5 wt.% solution of the copolymer. The absorption in a one cm cell at 485 nm was 0.424 + 0.007 for the microemulsion polymerized copolymer and 0.0795 + 0.005 for the copolymer made in the absence of microemulsion. This latter value is indistinguishable from the absorption of water saturated with dye. This is evidence that the water polymerized product of Example 3 did not incorporate the hydrophobic dodecyl acrylamide, while the microemulsion polymerized products of Example 3 did incorporate dodecyl acrylamide. EXAMPLE 5 Acrylamide/Dodecyl Acrylamide Copolymers Copolymers of acrylamide and dodecyl acrylamide were prepared, according to the procedure of Example 3, with different mole fractions of dodecyl acrylamide, y, that were initially contained in the polymerization vessel. These copolymers were isolated, purified and redissolved in water to give solutions with known concentrations. The viscosities of these solutions were measured by the previously described method. Figure 1, therefore, shows that the degree of polymerization of the copolymers and homopolymer are very nearly all equal, and that introduction of the dodecyl acrylamide produces a beneficial enhancement in viscosity. Values for the reduced viscosities of some of these systems are shown in Table I at a polymer concentration of one percent, in water and also in a two percent sodium chloride solution. These data show that the viscosities are not lowered by the salt. This is also illustrated in Figure 2, which shows that the relative salt independence is not a function of polymer concentration. This salt independence of the copolymers sharply contrasts with that exhibited by the well-known acrylamide/acrylic acid copolymers. TABLE I Alkyl Acrylamide-Acrylamide Copolymer Compositions and Reduced Viscosities RAM AM(Mol.%) nsp/C (dR/g) (a) r15p/C (2% Salt) (dg/g)(a) - 100 5.2 C12 99.5 7.8 8.4 C12 99.0 18.4 16.5 C12 98.0 32.1 34.7 C12 80.0 -(b) ,(b) C8 99.5 8.3 8.5 C8 99 18.3 19.7 C8 98 308 306 (a)At 1% polym. concn. (b)Insoluble in H20. EXAMPLE 6 Acrylamide/Octyl Acrylamide Copolymers Copolymers of acrylamide/octyl acrylamide were prepared according to the procedure of Example 3. Figure 3 gives results for their reduced viscosity as a function of concentration in aqueous solutions for the formed copolymers. These plots clearly demonstrate the improved thickening efficiency resulting from the introduction of a small mole fraction of octyl acrylamide into the polymer. The salt independence of the viscosity is also shown in Table I. Plots with and without 2% salt are compared in Figure 4 for the 98/2 acrylamide/octyl acrylamide copolymer0 EXAMPLE 7 Drag Reduction of Novel Copolymers Drag reduction effectiveness was evaluated by flowing polymer/distilled water solutions through a 2.13 mm inside diameter stainless steel tube and measuring the resulting frictional pressure drop. Flows were generated by first loading a bladder accumulator with a previously dissolved polymer/distilled water solution and then discharging the solution through the tube test section. The bladder accumulator used (Greer-Olaer Model 30A - 2 1/2) is a 10Q pressure vessel which contains an inflatable rubber bladder, a port for loading and discharging gas from the inside of the bladder and a port for loading and discharging liquid solutions from the space between the bladder and the interior vessel walls. To load the vessel with liquid, the bladder was first expanded with nitrogen gas such that the bladder filled the inside of the vessel. The liquid solution was then siphoned into the vessel as the bladder was evacuated. Subsequent charging of the vessel with nitrogen gas produced a flow of liquid which was directed to the 2.13 mm diameter tube. Pressure drops were measured across a 48 cm straight segment of the tube with a pair of flush mounted tube wall pressure taps and a differential pressure transmitter. Flow rates were measured by weighing samples of the effluent liquid collected over measured time periods. Flow rates in the drag reduction experiments ranged from about 8 to 20 g/s; these correspond to solvent Reynolds numbers from about 5000 to 13000 (solvent Reynolds number = mean flow velocity x tube diameter + solvent kinematic viscosity). Drag reduction was measured by comparing pressure drops of the polymer/distilled water solutions with pressure drops of the distilled water solvent at equal flow rates. Results were expressed as percent drag reduction which is defined as follows: EMI14.1 <tb> <SEP> Pressure <SEP> Drop <SEP> - <SEP> Pressure <SEP> Drop <tb> Percent <SEP> Drag <SEP> Reduction <SEP> = <SEP> (Solvent) <SEP> (Solution) <SEP> ) <SEP> x <SEP> 100 <tb> <SEP> Pressure <SEP> Drop <SEP> Reduction <SEP> = <SEP> Pressure <SEP> Drop <SEP> (Solvent) <tb> Typical drag reduction results from experiments with several novel acrylamide copolymer solutions are given in Table I. Significant drag reduction was observed for all listed solutions. Each solution contained 89 parts per million (by weight) of polymer. TABLE I DRAG REDUCTION DATA Hydrophobe Solvent Drag Level Reynolds Reduction Sample Type (Mole %) Number (%) 1 C8 1.5 10,300 20 2 C8 1.0 10,500 37 3 C8 0.75 10,300 47 4 C8 0.5 10,400 33 5 C12 0.5 10,500 51 6 C8 0.25 10,500 52

Claims: CLAIMS: 1. A free radical copolymerization process - for the formation of a copolymer of acrylamide/alkyl acrylamide which comprises the steps of: (a) forming a surfactant solution; (b) forming a deaerated reaction solution from said surfactant solution, water, acrylamide monomer and alkyl acrylamide monomer; (c) adding sufficient quantity of initiator to initiate copolymerization of said acrylamide monomer and said alkyl acrylamide monomer in said reaction solution; and (d) polymerizing said acrylamide monomer and said alkyl acrylamide monomer in said reaction solution for a sufficient period of time and a sufficient temperature to form said copolymer. 2. A free radical copolymerization process according to claim 1 which includes means for recovering said copolymer from said reaction solution. 3. A free radical copolymerization process according to either of claims 1 and 2, wherein said:copolymer has the formula: EMI15.1 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 %. 4. A free radical copolymerization process according to claim 3, wherein said R1 is an alkyl group having about 6 to about 18 carbon atoms. 5. A free radical copolymerization process according to claim 3 or claim 4 wherein x is 95.0 to 98.0 mole % and y is 0. 2to 5.0 mole %. 6. A free radical copolymerization process according to any one of the preceding claims wherein said surfactant solution comprises a mixture of a surfactant, an alcohol and an alkane solvent. 7. A copolymer having the formula: EMI16.1 wherein R1 having 6 to 22 carbon atoms, is an alkyl group, straight chained or branched or cycloalkyl group, R2 is the same or different alkyl group as R1 oris hydrogen, x is 90.0 to 99.9 mole %, and y is 10 to 0.1 mole t. 8. A copolymer according to claim 7, wherein R1 is an alkyl group having 6 to about 20 carbon atoms. 9. A copolymer according to claim 7 wherein R is an alkyl group having 6 to 18 carbon atoms. 10. The use of the copolymer according to any one of claims 7 to 9 as a drag reduction agent.

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