Emulsion Polymerizations with 2-Acrylamido-2-methylpropanesulfonic

Chapter 5 Emulsion Polymerizations with 2-Acrylamido-2-methylpropanesulfonic Acid 1

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Geoffrey P. Marks and Alan C. Clark

Downloaded by UNIV OF GUELPH LIBRARY on September 7, 2012 | http://pubs.acs.org Publication Date: March 27, 2000 | doi: 10.1021/bk-2000-0755.ch005

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Lubrizol International Laboratories, P.O. Box 88, Belper, Derby DE56 1QN, United Kingdom The Lubrizol Corporation, 29400 Lakeland Boulevard, Wickliffe, OH 44092-2298

There is a growing need to improve the properties of latices to be used in applications such as paper coatings, pressure-sensitive adhesives, paints, carpet backing and personal care formulations. Desired attributes include improved compatibility of latices with divalent cation salts such as calcium carbonate, better latex particle mechanical stability under high shear conditions to avoid coagulation, improved adhesion and enhanced durability of coatings towards water washing. Three types of latex formulations have been prepared with sodium 2-acrylamido-2methyl-1-propanesulfonate, A M P S sodium salt monomer , replacing most of the surfactants and acrylic acid in an acrylic latex, replacing sodium vinyl sulfonate in a vinyl acrylic latex and replacing methacrylic acid in a styrene acrylic latex. The divalent cation stability of both the acrylic and the styrene acrylic latices were significantly improved by replacing the carboxylate monomers with A M P S sodium salt. The scrub resistance of paints made from the acrylic and styrene acrylic latices prepared with A M P S sodium salt were also significantly improved. ®

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Three types of latex formulations have been prepared. The first formulation is an acrylic latex from methyl methacrylate, butyl acrylate and acrylic acid using sodium lauryl sulfate and Synperonic® NP20 (an ethoxylated nonylphenol) as surfactants. The second formulation is a vinyl acrylic latex from vinyl acetate, butyl acrylate and sodium vinyl sulfonate with sodium lauryl sulfate as the surfactant. The third formulation is a styrene acrylic latex from styrene, butyl acrylate and methacrylic acid with sodium lauryl sulfate as the surfactant. Three experimental latex formulations analogous to the three above were also prepared with A M P S sodium salt replacing acrylic acid, sodium vinyl sulfonate and methacrylic acid respectively. 2

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© 2000 American Chemical Society

In Specialty Monomers and Polymers; Havelka, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

47 Experimental


Each of the following six latex preparations was prepared by a semi-continuous, twostep procedure. In step one, 5-10%w of the monomers were added to water containing all of the required surfactant and more than 5-10w% of the catalyst. In step two, additional catalyst was added and the remainder of the monomers was added continuously over several hours. When AMPS sodium salt was one of the monomers, it was added continuously as a separate feed from the other monomers. Baseline Acrylic Latex Preparation. A solution of sodium lauryl sulfate(3.53 g), Synperonic NP20 (10.36 g) and sodium bicarbonate (1.43 g) in 420 grams of water was prepared and purged subsurface with nitrogen to remove oxygen. The solution was heated to 80°C and a mixture of methyl methacrylate (37.8 g, 0.378 mol), butyl acrylate (30.8 g, 0.24 moles) and acrylic acid (1.4 g, 19 mmol) was added. After the temperature returned to 80°C, a solution of sodium persulfate (0.7g, 2.94 mmol) in 10 g of water was added. After 30 minutes, A mixture of methyl methacrylate (340 g, 3.40 moles), butyl acrylate (277 g, 2.16 moles) and acrylic acid (12.6 g, 0.17 moles) was added at a rate of 280 g per hour. After 30 minutes of monomer addition, a solution of sodium persulfate (3.5 g, 14.7 mmol) in 140 g of water was added at a rate of 55 grams per hour. When addition of all of the ingredients was complete, the latex was stirred under nitrogen for an additional 30 minutes, decanted and cooled. Experimental Acrylic Latex Preparation. Prepare a solution of sodium lauryl sulfate (0.36 g) and sodium bicarbonate (1.4 g) in 403 grams of water at 80°C and purge the solution subsurface with nitrogen to remove oxygen. Add a mixture of methyl methacrylate (38.0 g, 0.38 moles) and butyl acrylate (31.2 g, 0.243 moles) to the solution. Add aqueous 50% A M P S sodium salt (1.4 g, 3.06 mmol) to the solution. After the temperature returned to 80°C, a solution of sodium persulfate (0.7, 2.94 mmol) in 10 g of water was added. After 30 minutes, a mixture of methyl methacrylate (342 g, 3.42 moles) and butyl acrylate (281 g, 2.19 moles) was added at a rate of 280 grams per hr. Aqueous 50% AMPS sodium salt (12.6 g, 27.5 mmol) in 140 g of water was added simultaneously at 70 g per hour. After 30 minutes of monomer addition, a solution of sodium persulfate (3.5 g, 14.7 mmol) in 140 g of water was added at a rate of 55 grams per hour. When addition of all of the ingredients was complete, the latex was stirred under nitrogen for an additional 30 minutes, decanted and cooled. Table 1 compares the baseline and experimental acrylic latex formulations. Baseline Vinyl Acrylic Latex Preparation. A solution of sodium lauryl sulfate (9.1 g) and sodium bicarbonate (1.34 g) in 428 grams of water was prepared and heated to 84°C. Purge the solution subsurface with nitrogen to remove oxygen. After one hour of nitrogen purging, a mixture of vinyl acetate (18.0 g, 0.21 moles) and butyl acrylate (4.51 g, 0.035 moles), potassium persulfate (2.04 g, 7.55 mmol) and sodium vinyl sulfonate monomer (0.90 g, 1.73 mmol) was added. SVS was supplied as a 25% aqueous solution. After the reflux subsided, a mixture of vinyl acetate (343 g, 3.98 moles) and butyl acrylate (85.7 g, 0.665 moles) was added to the reaction mixture at

American Chemical Society Library 16thandSLH.W. In Specialty 1155 Monomers Polymers; Havelka, K., et al.; ACS Symposium Series; American Chemical Washington* 0 £ Society: 20Q36 Washington, DC, 2000.

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120 g per hour simultaneously with a mixture of SVS (17.1 g, 32.9 mmol) with water (40.9 g). The reaction mixture was stirred for an additional 30 minutes. A mixture of sodium formaldehyde bisulfite (0.18 g, 0.67 mmol) with water (1.3 g) was added in one-third portions every 10 minutes. A solution of /-butylhydroperoxide (0.18 g, 1.40 mmol) in water (1.3 g) was added in one-half portions at the same time as the first two sodium formaldehyde bisulfite additions. Once the additions were complete the temperature was lowered, the nitrogen purge was removed, and the mixture was allowed to cool to room temperature overnight. Experimental Vinyl Acrylic Latex Preparation. A solution of sodium lauryl sulfate (9.1 g) and sodium bicarbonate (1.34 g) in 428 grams of water was prepared. Purge the solution subsurface with nitrogen to remove oxygen and heat to 84°C. After one hour of nitrogen purging, a mixture of vinyl acetate (18.0 g, 0.21 moles) and butyl acrylate (4.51 g, 0.035 moles), potassium persulfate (2.04 g, 7.55 mmol) and 50% aqueous A M P S sodium salt (0.45g, 0.98 mmol) was added. After the reflux subsided, A mixture of vinyl acetate (343 g, 3.98 moles) and butyl acrylate (85.7 g, 0.665 moles) was added to the reaction mixture at 120 g per hour simultaneously with 50% aqueous A M P S sodium salt (8.55g, 18.7 mmol) in 40.9 g water. The reaction mixture was stirred for an additional 30 minutes. A mixture of sodium formaldehyde bisulfite (0.18 g, 0.67 mmol) with water (1.3 g) was added in one-third portions every 10 minutes. A solution of f-butyl -hydroperoxide (0.18 g, 1.40 mmol) in water (1.3 g) was added in one-half portions at the same time as the first two sodium formaldehyde bisulfite additions. Once the additions were complete, the temperature was lowered, the nitrogen purging was stopped and the mixture was allowed to cool to room temperature overnight. Table 2 compares the baseline and experimental vinyl acrylic formulations. Baseline Styrene Acrylic Latex Preparation. A solution of sodium lauryl sulfate (0.364 g) and sodium bicarbonate (1.4 g) in 395 g of water was prepared, adjusted to pH=9 by the addition of 15 drops of a 20%w NaOH solution and heated to 80°C. Purge the solution subsurface with nitrogen to remove oxygen. Note: If the pH adjustment is not made, the product latex is coagulated. A mixture of styrene (36.0 g, 0.346 moles) and butyl acrylate (32.6 g, 0.254 moles) was added to the solution. A solution of methacrylic acid (0.7g, 8.13 mmol) neutralized with 20% NaOH in 14.6 g of water was added to the solution. When the temperature returned to 80°C, a solution of sodium persulfate (0.70 g, 2.94 mmol) in 10 grams of water was added. After 30 minutes, a mixture of styrene (324 g, 3.11 moles) and butyl acrylate (293.4 g, 2.286 moles) was added at a rate of 279 grams per hour. A solution of methacrylic acid (6.3g, 73.2 mmol) neutralized with 20% NaOH in 131.7 g of water was added to the solution as a separate feed. After 30 minutes of monomer feed, a solution of sodium persulfate (3.5 g, 14.7 mmol) in 140 g of water was added at 62 grams per hour. When all of the additions were complete, the latex was stirred under nitrogen for an additional 30 minutes and decanted to cool.


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Table 1. Acrylic Latex Formulations Baseline Latex 29.3 23.9 1.1 0

Experimental Latex 30.3 24.9 0 0.6

Sodium Lauryl Sulfate

0.27

0.03

S y n p e r o n i c ® NP20

0.80

0

Sodium Bicarbonate Sodium Persulfate

0.11 0.32

0.11 0.33

Total Water Total Ingredients

44.2 100

43.8 100


Ingredient Methyl methacrylate Butyl acrylate Acrylic Acid Aqueous A M P S Sodium Salt (active part)

Table 2. Vinyl Acrylic Latex Formulations Ingredient Vinyl Acetate Butyl acrylate Sodium Vinyl Sulfonate (active part) Aqueous A M P S Sodium Salt (active part) Sodium Lauryl Sulfate Sodium Bicarbonate Potassium Persulfate Sodium Formaldehyde Bisulfite f-Butylhydroperoxide Total Water Total Ingredients

Baseline Latex 37.8 9.46 0.47 0

Experimental Latex 37.8 9.46 0 0.47

0.95 0.14 0.21 0.02 0.02

0.95 0.14 0.21 0.02 0.02

50.87 100

50.87 100



50 Experimental Styrene Acrylic Latex Preparation. A solution of sodium lauryl sulfate (0.364 g) and sodium bicarbonate (1.4 g) in 395 g of water was prepared. Purge the solution subsurface with nitrogen to remove oxygen. A mixture of styrene (36.0 g, 0.346 moles) and butyl acrylate (32.6 g, .254 moles) and a 50% aqueous solution of A M P S sodium salt (1.4g, 3.06 mmol) were added as a separate feeds to the aqueous solution. When the temperature returned to 80°C, a solution of sodium persulfate (0.70 g, 2.94 mmol) in 10 grams of water was added. After 30 minutes, a mixture of styrene (324 g, 3.114 moles) and butyl acrylate (293.4 g, 2.286 moles) was added at a rate of 279 grams per hour. A 50% aqueous solution of A M P S sodium salt (12.6g, 27.5 mmol) in 140 grams of water was added at 68 grams per hour as a separate feed. After 30 minutes of monomer feed, a solution of sodium persulfate (3.5 g, 14.7 mmol) in 140 g of water was added at 62 grams per hour. When all of the additions were complete, the latex was stirred under nitrogen for an additional 30 minutes and decanted to cool. Table 3 compares the baseline and the experimental styrene acrylic formulations. Paint preparation. Interior eggshell paints were prepared from the acrylic and the styrene acrylic latices in a manner typical of the decorative paint industry reflecting commonplace commercial practices and basic ingredients. The paints had a pigment volume concentration of 37% and a total solids content of 53%. A silk paint was prepared from a vinyl acrylic latex in a manner typical of the decorative paint industry reflecting commonplace commercial practices and basic ingredients. The paint had a pigment volume concentration of 35% and a total solids content of 45%. Results and Discussion The acrylic latex properties, Table 4, and the styrene acrylic latex properties, Table 5, showed a similar response to the use of A M P S sodium salt which is distinctly different than the response of the vinyl acrylic latex, Table 6. Acrylic and styrene acrylic latices containing AMPS sodium salt had significantly better stability towards cations and more than a 50% reduction in grit. The experimental acrylic latex, which was prepared with almost no surfactant, had a larger latex particle size than the baseline and correspondingly the Brookfield viscosity and the mechanical stability were reduced. If some sodium lauryl sulfate had been retained in the experimental formulation, it is expected that the particle size, Brookfield viscosity and mechanical stability would be closer to the baseline formulation values. The reduction in freeze/thaw stability is likely the absence of the non-ionic surfactant. The experimental styrene acrylic recipe retained the surfactant used in the baseline and both the latex particle size and Brookfield viscosity were unchanged. The mechanical stability was improved over the baseline. The experimental vinyl acrylic latex had slightly smaller latex particles, less grit and a higher Brookfield viscosity than the baseline; but the most significant improvement was in mechanical stability. A l l six of the latices were formulated into paints and the scrub resistance measured for each, Table 7. The baseline acrylic was good for only 775 cycles, but the experimental acrylic was good for 3500 cycles. The baseline styrene acrylic lasted longer, 3820 cycles, than the experimental acrylic latex but the experimental styrene acrylic was


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Table 3. Styrene Acrylic Latex Formulations

Baseline Latex

Experimental Latex

25.9 23.4 0.5 0

25.9 23.4 0 0.5

Sodium Lauryl Sulfate Sodium Bicarbonate Sodium Persulfate

0.026 0.1 0.3

0.026 0.1 0.3

Total Water

49.7

49.8

Total Ingredients

100

100


Ingredient Styrene Butyl acrylate Methacrylic Acid Aqueous A M P S ® Sodium Salt (active part)

Table 4. Acrylic Latex Properties

Nonvolatiles (%),ASTM D 4758 Cation Stability: ml of 5% CaCl PH Particle size (nm) Polydispersity coefficient Grit(ppm), A S T M D 5 0 9 7 Minimum film forming °C, A S T M D 2354 Mechanical stability, (min to 5 poise) Freeze/thaw stability (cycles to fail), A S T M D 2243 Brookfield cP, Spindle R2 @ 20 rpm 2

Baseline Latex 49.30 1 4.5 140 0.107 470 17-18 >10min >5 240

Experimental Latex 50.14 >40 6.9 220 0.069 210 17-18 3.42 min 1 74


52 Table 5. Styrene Acrylic Latex Properties

Baseline Latex 50.39 1 7.19 281 0.091 300 23-24 4.70 1 55

Nonvolatiles, % A S T M D4758 Cation Stability: ml of 5% CaCl PH Particle size (nm) Polydispersity coefficient Grit (ppm) A S T M D5097 Minimum film forming °C A S T M D2354 Mechanical stability, (min to 5 poise) Freeze/thaw stability (cycles to fail) A S T M D2243 Brookfield Vis., Spindle R2 @ 20ipm


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Experimental Latex 50.41 >25 6.9 280 0.102 120 20-21 8.35 1 59

Table 6. Vinyl Acrylic Latex Properties

Nonvolatiles (%), A S T M D4758 Cation Stability: ml of 5% CaCl PH Particle size (nm) Polydispersity coefficient Grit (ppm), A S T M D5097 Minimum film forming °C, A S T M D2354 Mechanical stability, (min to 5 poise) 2

Freeze/thaw stability (cycles to fail), A S T M D2243 Brookfield cP, Spindle R2 @ 20rpm

Baseline Latex 49.10 18 5 147 0.05 90 9-10 Coagulated (2J4minutes 1 54

Experimental Latex 48.58 17 4.8 132 0.13 60 9-10 >10 minutes 1 170

Table 7. A S T M D 2486 Paint Scrub Resistance Comparisons Paint Acrylic baseline (eggshell) Acrylic experimental (eggshell) Vinyl acrylic baseline (silk) Vinyl acrylic experimental (silk) Styrene acrylic baseline (eggshell) Styrene acrylic experimental (eggshell)

Scrub cycles 775 3500 655 687 3820 5700


53 even better at 5700 cycles. Both the vinyl acrylic baseline and the experimental paints gave poor performance. The properties that A M P S appears to impart to a latex formulation suggest that AMPS performs two different roles. Although AMPS is certainly hydrophilic, it is not a surfactant. However, AMPS is capable of copolymerizing with hydrophobic monomers to form polymers which can function as surfactants. Gibbs et al showed that a copolymer of 1 mole of A M P S and 6 moles of methyl methacrylate was an effective polymeric surfactant for the emulsion polymerization of styrene and styrene/butyl acrylate. Independently, Peiffer et al ' showed that AMPS/styrene copolymers containing 40% to 60% A M P S behave as polymeric surfactants. Shild et al studied the effect of A M P S on polystyrene coagulum, particle size, surface charge density, and latex stability in detail. It was also concluded that the formation of a polyelectrolyte from the homopolymerization of AMPS and its absorption on the surface of latex particles was possible and could contribute to latex stability. Corner investigated the stabilization of polystyrene latices by polyelectrolytes, including A M P S homopolymer. The in situ formation of an AMPS homopolymer during emulsion polymerization seems unlikely unless the rate of AMPS addition is fast. The formation of copolymer polyelectrolytes seems much more likely. These copolymers, which will contain both nonionic hydrophobic and anionic hydrophilic segments may be more effective protective colloids than AMPS homopolymer. Recently, a vinyl acrylic latex process , a butadiene/styrene latex process and an acrylic latex process using A M P S sodium salt have been patented. 3


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Conclusion It has been demonstrated that AMPS® Monomer can be an effective partial replacement for surfactants and other water-soluble monomers in three common types of latex formulations: acrylic, vinyl acrylic and styrene acrylic. Improved latex properties and improved scrub resistance of coatings prepared from these latices have been demonstrated.

References 1. A M P S is a trademark of The Lubrizol Corporation. 2. Synperonic is a trademark of The ICI Corporation. 3. US 3,965,032 assigned to The Dow Company. 4. Peiffer, D. G.; K i m , M. W.; Kaladas, J. Polymer 1988, 29, 716-723. 5. Wang, Z.; Wang, J.; Chu, B.; Peiffer, D. G. J. Polym. Sci.: Part B: Polym. Phys. 1991, 29, 1361-1371. 6. Schild, R. L.; El-Aasser, M. S.; Poehlein, G. W.; Vanderhoff, J. W. Emulsions, Latices, Dispersions 1978, 99-128 Edited by Becher, P; Yudenfreund, M. N.; Marvin N. Dekker; New York, N.Y. 7. Corner. T.: Colloids and Surfaces 1981, 3, 119-129. 8. US 4,812,510 assigned to The Glidden Company. 9. US 5,274,027; US 5,302,655 assigned to The Dow Chemical Company. 10. EP 770,655 A2, assigned to Rohm and Haas Company.


Emulsion Polymerizations with 2-Acrylamido-2-methylpropanesulfonic

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