Preparation of aqueous dispersions of acrylate-silicone copolymer particles

Abstract

The present invention is a process for preparing an aqueous dispersion of copolymer particles comprising structural units of: a) an acrylate monomer; b) an acid monomer; and c) a siloxane-acrylate monomer of formula (I), wherein R, R 1 , R 2 , Y and x are defined herein. The process further requires the use of a special class of anionic and nonionic surfactants as described herein. The aqueous dispersions prepared by the process of the present invention can be used in a variety of applications ranging from architectural coatings to personal care products.

Description

BACKGROUND

[0001] The present invention relates to aqueous dispersions of copolymer particles comprising structural units of acrylate monomers and siloxane-acrylate monomers. The compositions of the present invention are useful in coating and personal care applications.

[0002] Aqueous hybrid latex compositions comprising copolymer particles functionalized with acrylate and siloxane groups provide improved performance in coating and cosmetic applications such as improved stain and solvent resistance, water and oil repellency, non-biofouling properties, and increased tactile feedback compared to all acrylate compositions.

[0003] Xiao, J. et al. (Prog. Org. Coat. 2018, 116, 1-6) and Zhang, B. et al. (Appl. Surf. Sci. 2007, 254, 452-458) report the preparation of polymer dispersions of siloxane-acrylate hybrid particles. However, the present inventors have shown that the methods used to prepare these dispersions result in latices with high levels of gel and unreacted monomer. The formation of high concentrations of gel is a strong indicator of low process efficiency, which can lead to reactor fouling and result in the deterioration of the properties of the final coating. Furthermore, the concentration of siloxane-containing monomer incorporated in each of these reported methods is significantly less than 10 wt%, which limits the effectiveness of the dispersions. It is widely accepted that achieving relatively high levels of incorporated siloxane-containing monomer in the final dispersed copolymer particles (e.g., > 20 wt%) results in improvements in coating and personal care formulation additives in terms of siloxane-containing oligomers and polymers of interest properties.

[0004] Accordingly, it would be advantageous to prepare aqueous dispersions of siloxane-acrylate copolymer particles functionalized with structural units of relatively high concentrations of siloxane-containing monomers. SUMMARY

[0005] The present invention addresses the needs in the art by providing a method of preparing an aqueous dispersion of acrylate-siloxane copolymer particles, the method comprising the steps of:

[0006] 1) adding a first portion of an aqueous monomer emulsion to a vessel containing water and an anionic surfactant, wherein the contents of the vessel are stirred and controlled at a temperature in the range of 60 °C to 95 °C;

[0007] 2) adding a first portion of an initiator to the vessel to form an aqueous dispersion of seed copolymer particles over time; then

[0008] 3) adding a second portion of the monomer emulsion and a second portion of the initiator to the vessel; then

[0009] 4) maintaining the temperature of the contents of the vessel in the range of 60°C to 95°C for a sufficient length of time to achieve substantially complete conversion of the monomers in the monomer emulsion to polymer particles comprising the monomers as structural units;

[0010] wherein the average monomer droplet size of the monomer emulsion is in the range of 1 pm to 30 pm, and comprises, based on the weight of the monomers, a) 40 wt% to 98.8 wt% of an acrylate monomer; b) 0.1 wt% to 5 wt% of an acid monomer; c) 1 wt% to 59.8 wt% of a siloxane acrylate monomer; 0.5 wt% to 5 wt% of a non-ionic surfactant; and 0.5 wt% to 5 wt% of an anionic surfactant;

[0011] wherein the siloxane acrylate monomer is represented by Formula I:

[0012]

[0013] wherein R is H or CH3;

[0014] R 1 is H or CH3;

[0015] each R 2 is independently CH3or O-Si(CH3)3;

[0016] Y is -CH2- or -CH2CH2-; and

[0017] x is 0 or 1 ;

[0018] provided that when x is 1, R 1 is H; when Y is -CH2-, R 1 is H; and when Y is -CH2CH2-, R 1 is CH3and x is 0;

[0019] wherein the non-ionic surfactant is represented by Formula II:

[0020]

[0021] wherein n is 0 to 10; p is 2 to 30, provided that p > n; and R 3 is a linear or branched C3-C 16 alkyl group; and

[0022] wherein the anionic surfactant is represented by Formula III:

[0023]

[0024] wherein R 4 is C6-C 20alkyl; m is 0 to 10; and M is Li, Na, or K.

[0025] The present invention addresses the needs in the art by providing a way to increase the incorporation of siloxane-based monomers into copolymer particles with minimal gel formation. DETAILED DESCRIPTION

[0026] The present invention is a method of making an aqueous dispersion of acrylate-silicone copolymer particles, the method comprising the steps of:

[0027] 1) adding a first portion of an aqueous monomer emulsion to a vessel containing water and an anionic surfactant, wherein the contents of the vessel are stirred and temperature controlled at a temperature in the range of 60°C to 95°C;

[0028] 2) adding a first portion of an initiator to the vessel to form an aqueous dispersion of seed polymer particles over time; then

[0029] 3) adding a second portion of the monomer emulsion and a second portion of the initiator to the vessel; then

[0030] 4) maintaining the temperature of the contents of the vessel in the range of 60°C to 95°C for a time sufficient to achieve substantially complete conversion of the monomers in the monomer emulsion to polymer particles comprising structural units of the monomers;

[0031] wherein the average monomer droplet size of the monomer emulsion is in the range of 1 pm to 30 pm and comprises, based on the weight of the monomers, a) 40 wt% to 98.8 wt% of an acrylate monomer; b) 0.1 wt% to 5 wt% of an acid monomer; c) 1 wt% to 59.8 wt% of a siloxane acrylate monomer; 0.5 wt% to 5 wt% of a non-ionic surfactant; and 0.5 wt% to 5 wt% of an anionic surfactant;

[0032] wherein the siloxane acrylate monomer is represented by Formula I:

[0033]

[0034] wherein R is H or CH3;

[0035] R 1 is H or CH3;

[0036] each R 2 is independently CH3or O-Si(CH3)3;

[0037] Y is -CH2- or -CH2CH2-; and

[0038] x is 0 or 1 ;

[0039] provided that when x is 1, R 1 is H; when Y is -CH2-, R 1 is H; and when Y is -CH2CH2-, R 1 is CH3and x is 0;

[0040] wherein the nonionic surfactant is represented by Formula II:

[0041]

[0042] wherein n is 0 to 10; p is 2 to 30, provided that p > n; and R 3 is a linear or branched C3-C 16 alkyl group; and

[0043] wherein the anionic surfactant is represented by Formula III:

[0044]

[0045] wherein R 4 is a C6-C 20 alkyl; m is 0 to 10; and M is Li, Na, or K.

[0046] As used herein, the term “structural unit” of a specified monomer refers to the residue of the monomer after polymerization. For example, the structural unit of methyl methacrylate (MMA) is illustrated as follows:

[0047]

[0048] wherein the dashed line indicates the point of attachment of the structural unit to the polymer backbone.

[0049] As used herein, “substantially complete conversion of monomers” means at least 98%, preferably at least 99% conversion of total monomers to copolymer particles.

[0050] As used herein, the term “acrylate monomer” refers to one or more acrylate and / or methacrylate monomers. Examples of suitable acrylate monomers include MAA, n-butyl methacrylate (BMA), ethyl acrylate (EA), n-butyl acrylate (BA), and 2-ethylhexyl acrylate (2-EHA). Preferably, at least 80% by weight, and more preferably at least 90% by weight of the acrylate monomers are a combination of MAA and BA.

[0051] Examples of suitable acid monomers include carboxylic acid monomers, phosphoric acid monomers, and sulfuric acid monomers. Examples of preferred carboxylic acid monomers include acrylic acid (AA), methacrylic acid (MAA), and itaconic acid (IA), and salts thereof.

[0052] Suitable phosphoric acid monomers include phosphonates and dihydrogen phosphates of alcohols containing a polymerizable vinyl or alkenyl group or substituted with a polymerizable vinyl or alkenyl group. Preferred dihydrogen phosphates are phosphates of hydroxyalkyl acrylate or methacrylate, including phosphoethyl methacrylate (PEM) and phosphopropyl methacrylate.

[0053] Examples of suitable sulfuric acid monomers include methacrylate ethanesulfonate, methacrylate propanesulfonate, styrene sulfonic acid, vinyl sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and salts thereof.

[0054] In one aspect, the weight ratio of BA to MMA is in the range of 45:55 to 55:45; in another aspect, the weight ratio of acrylate monomers (preferably BA and MMA) to acid monomers (preferably MAA) is in the range of 99.95:0.05, more preferably 99.5:0.5 to 97:3, more preferably to 98:2.

[0055] Preferred ranges of siloxane-acrylate monomers of Formula I depend on the application. For home and personal care applications, such as cosmetics, hair care, and skin care, for example, the weight percent of monomers of Formula I (based on the weight of the total monomers) is preferably in the range of 20 wt%, more preferably 30 wt%, and most preferably 45 wt% to 55 wt% (based on the weight of the copolymer particles). For coating applications, the preferred weight percent is in the range of 2 wt%, more preferably 3 wt% to 20 wt%, to 15 wt%, and most preferably to 10 wt% (based on the weight of the copolymer particles).

[0056] Examples of monomers of Formula I include:

[0057]

[0058]

[0059] Nonionic surfactants of Formula II preferably comprise branched alkyl groups; n is preferably in the range of 0 to 5; and p is preferably in the range of 3 to 16. Examples of suitable commercial nonionic surfactants include TERGITOL 15-S-9 nonionic surfactant (15-S-9; trademark of Dow Chemical Company or its affiliates), TERGITOL TMN-3 nonionic surfactant (TMN-3), TERGITOL TMN-6 nonionic surfactant (TMN-6), TERGITOL TMN-10 nonionic surfactant (TMN-10), ECOSURF TM 15-S-9 nonionic surfactant (15-S-9; trademark of Dow Chemical Company or its affiliates), TERGITOL TMN-3 nonionic surfactant (TMN-3), TERGITOL TMN-6 nonionic surfactant (TMN-6), TERGITOL TMN-10 nonionic surfactant (TMN-10), ECOSURF TMEH-6 nonionic surfactant (EH-6; trademark of Dow Chemical Company or its affiliates). The structure of these surfactants is shown below:

[0060]

[0061] The anionic surfactant of Formula III is preferably a linear C 10 -C 14 alkyl sulfate, where m is 0. A preferred anionic surfactant is sodium lauryl sulfate (SLS). The concentration of the anionic surfactant of Formula III is preferably in the range of 1 wt% to 3 wt% based on the weight of monomer; the weight ratio of anionic surfactant to nonionic surfactant is preferably in the range of 1 :2 to 2: 1.

[0062] A method for preparing an aqueous dispersion of acrylate-silicone copolymer particles, the method comprising the steps of:

[0063] 1) adding a first portion of an aqueous monomer emulsion to a vessel containing water, an anionic surfactant, and preferably a nonionic surfactant, where the contents of the vessel are stirred and controlled at a temperature preferably in the range of 80°C to 95°C;

[0064] 2) adding a first portion of initiator to the vessel to form an aqueous dispersion of seed polymer particles over time; then

[0065] 3) gradually adding a second portion of monomer emulsion and a second portion of initiator to the vessel; then

[0066] 4) maintaining the temperature of the contents of the vessel preferably in the range of 80°C to 95°C for a time sufficient to achieve at least 99% conversion of monomer to copolymer particles comprising monomeric structural units.

[0067] Preferably, after step 4), a redox initiator package is added to the vessel; it is also preferred that the aqueous dispersion is neutralized to a pH in the range of 6.5 to 7.5 after step 4). It is more preferred that the redox initiator package is added after step 4), followed by the neutralization.

[0068] It has been surprisingly discovered that high levels of siloxane-acrylate monomers of Formula I can be effectively incorporated into siloxane-acrylate copolymers by the method of the present invention without substantially forming coagulum (gels), as determined by gravimetric analysis, and large diameter particles (i.e., particles having a particle size > 1 pm and < 40 pm, as determined by single particle optical sensing as described herein).

[0069] Determination of suspended polymer levels by AccuSizer

[0070] The amount of suspended polymer in the copolymer particle dispersion was measured using an AccuSizer 7000 APS single particle optical sensor instrument (Particle Sizing Systems, PSS, an Entegris Company, Port Richey, FL). The copolymer particle dispersion was diluted 1000-fold by mass in MilliQ water and then injected into the sample chamber of the instrument. The experimental method applied a two-stage dilution of the injected sample, with a first dilution of 21.6 in the pre-dilution chamber and a second dilution of 78.4 in the second stage dilution area of the instrument. After data collection was complete, the sample chamber was rinsed with MilliQ water until a baseline threshold of less than 200 counts per milliliter was observed. The sampling method was set to measure approximately 100,000 total counts, and particles with a measured particle size > 1 pm were defined as suspended polymer. The samples were run in duplicate, and the data was presented as an average. Data was collected and processed using PSS software (version 2.3.1.6).

[0071] Example 1 - Preparation of aqueous dispersion of hybrid copolymer particles using a mixture of SLS and 15-S-9 nonionic surfactant

[0072] Deionized water (150.0 g), Polystep B-5-N sodium lauryl sulfate (SLS, 3.0 g, 28.0% aqueous solution), and 15-S-9 (3.0 g) were added to a 500 mL 4-necked round bottom flask, equipped with a condenser, overhead stirrer, and thermocouple. The contents of the reactor were stirred at 250 rpm and heated to 88 °C under N2. In a separate vessel, a monomer emulsion (ME) containing deionized water (180.0 g), SLS (14.1 g, 28.0% aqueous solution), 15-S-9 (3.0 g), BA (73.5 g), MMA (73.5 g), MAA (3.0 g), MD'M-ALMA (150.0 g), n-dodecyl mercaptan (n-DDM, 0.15 g), ammonium hydroxide solution (2.8 g, 28% active in water), and sodium acetate (0.9 g) was prepared using an overhead mixer and then treated with a hand-held homogenizer (TissueTearor, Model 985370, Biospec Products Inc.) for 1 min to produce a ME with an average droplet size of about 2-15 μm as determined by light microscopy. A portion of the ME (20.0 g) was added to the reactor and rinsed (5.0 g of water) before adding ammonium persulfate (APS, 0.09 g) and rinsing (2.0 g of water). The remaining ME and APS solution (0.32 g in 24.0 g of water) were fed simultaneously into the reactor over 120 min at a temperature of 87-88 °C. After the feed was complete, the reactor was held at 87-88 °C for an additional 30 min. The reactor was then cooled to 60 °C, after which separate solutions of (i) Luperox TAH 85 t-amyl hydroperoxide (t-AHP, 0.29 g, 85 wt% active in water), SLS (0.06 g, 28% active in water), and deionized water (3.0 g), and (ii) isoascorbic acid (IAA, 0.15 g), VERSENE TMEDTA (EDTA, trademark of Dow or its affiliates; 0.3 g, 1% active in water), and iron (II) sulfate solution (2.1 g, 0.15% active in water) were added to the reactor. The reactor was then cooled to room temperature, then ammonium hydroxide solution (28% active in water) was added dropwise to adjust the pH to ~7.0. The aqueous dispersion was filtered in sequence through stainless steel screens with pore sizes of 840 pm, 150 pm, and 40 pm. The final aqueous particulate dispersion had: 43.0% solids, a z-average particle size of 103 nm as determined by DLS, a final polymer coagulum (gels) level of 0.11 wt% (based on monomer; total of gels collected across each mesh size), and a suspended polymer (based on monomer) of 0.43 wt% as determined by Accusizer characterization. The level of residual MD'M-ALMA in the sample was determined to be <30 ppm by UHPLC.

[0073] Example 2 - Preparation of an aqueous dispersion of hybrid copolymer particles using a mixture of SLS and TMN-6 nonionic surfactant

[0074] Example 1 was repeated except that the 500 mL 4-necked round bottom flask and 15-S-9 nonionic surfactant in ME were replaced with an equal mass of TMN-6 nonionic surfactant. The final aqueous particulate dispersion had: 42.8% solids, a z-average particle size of 100 nm as determined by DLS, a final polymer gel level of 0.12 wt% (based on monomer; total of gels collected across each mesh size), and a suspended polymer (based on monomer) of 1.75 wt% as determined by Accusizer characterization. The level of residual MD'M-ALMA in the sample was determined to be <30 ppm by UHPLC.

[0075] Example 3 - Preparation of an aqueous dispersion of hybrid copolymer particles using a mixture of SLS and TMN-10 nonionic surfactant

[0076] Example 1 was repeated except that the 500 mL 4-necked round bottom flask and 15-S-9 nonionic surfactant in ME were replaced with an equal mass of TMN-10 nonionic surfactant. The final aqueous particulate dispersion had: 42.7% solids, a z-average particle size of 115 nm as determined by DLS, a final polymer gel level of 0.18 wt% (based on monomer; total of gels collected across each mesh size), and a suspended polymer (based on monomer) of 1.01 wt% as determined by Accusizer characterization. The level of residual MD'M-ALMA in the sample was determined to be <30 ppm by UHPLC.

[0077] Example 4 - Preparation of aqueous dispersion of hybrid copolymer particles using a mixture of SLS and EH-6 non-ionic surfactant

[0078] Example 1 was repeated except that 500 mL of a 4-necked round bottom flask and 15-S-9 non-ionic surfactant in ME were replaced with an equal mass of EH-6 non-ionic surfactant. The final aqueous particle dispersion had: 42.5% solids, a z-average particle size of 103 nm as determined by DLS, a final polymer gel level of 0.18 wt% (based on monomer; total gel collected on each sieve size), and 1.75 wt% of suspended polymer (based on monomer) as determined by Accusizer characterization. The level of residual MD'M-ALMA in the sample was < 30 ppm as determined by UHPLC.

[0079] Comparative Example 1 - Preparation of aqueous dispersion of hybrid copolymer particles using SLS

[0080] Example 1 was repeated except that 500 mL of a 4-necked round bottom flask and 15-S-9 non-ionic surfactant in ME were replaced with an equal mass of EH-6 non-ionic surfactant. The final aqueous particle dispersion had: 42.5% solids, a z-average particle size of 103 nm as determined by DLS, a final polymer gel level of 0.18 wt% (based on monomer; total gel collected on each sieve size), and 1.75 wt% of suspended polymer (based on monomer) as determined by Accusizer characterization. The level of residual MD'M-ALMA in the sample was < 30 ppm as determined by UHPLC.

[0081] Comparative Example 2 - Preparation of aqueous dispersion of hybrid copolymer particles using 15-S-9 non-ionic surfactant

[0082] Example 1 was repeated except that 500 mL of a 4-necked round bottom flask and 15-S-9 non-ionic surfactant in ME were replaced with an equal mass of EH-6 non-ionic surfactant. The final aqueous particle dispersion had: 42.5% solids, a z-average particle size of 103 nm as determined by DLS, a final polymer gel level of 0.18 wt% (based on monomer; total gel collected on each sieve size), and 1.75 wt% of suspended polymer (based on monomer) as determined by Accusizer characterization. The level of residual MD'M-ALMA in the sample was < 30 ppm as determined by UHPLC.

[0083] Comparative Example 3 - Preparation of aqueous dispersion of hybrid copolymer particles by the Xiao method

[0084] The method of preparing a hybrid particle aqueous dispersion as described by Xiao, J. et al. (Prog. Org. Coatings 2018, 116, 1-6) was reproduced. The synthesis was performed using a 500 mL, 4-necked round bottom flask equipped with a condenser, overhead stirrer, and thermocouple. Deionized water (19.0 g) and SLS (1.43 g, 28.0% aqueous solution), TRITON X-100 polyethylene glycol tert-octylphenyl ether (Dow or its affiliates’ trademark, 0.80 g), and sodium bicarbonate (NaHCO3; 0.40 g) were added to the flask. The contents of the reactor were stirred at 100 rpm and heated to 60 °C under N2. In a separate vessel, a ME containing deionized water (48.5 g), SLS (2.14 g, 28.0% aqueous solution), Triton X-100 (1.20 g), BA (BA; 44.8 g), MMA (42.3 g), styrene (10.1 g), and AA (1.9 g) was prepared using an overhead mixer. A portion of the ME (15.1 g) was added to the reactor, followed by APS (0.13 g) in deionized water (10.0 g), and the reactor temperature was increased to 80 °C over 10 min. The remaining ME and APS solution (0.27 g in 20.0 g water) were fed to the reactor simultaneously at a temperature of 80 °C to 81 °C over 4.5 h and 5 h, respectively (i.e., the APS feed continued for 30 min after the ME feed was complete). At the 3 h mark of the feeds, MD'M ALMA was added to the reactor (10.0 g). After the completion of the APS feed, the reactor was then held at 80 °C for an additional 30 min. The reactor was then cooled to room temperature and ammonium hydroxide solution (28% active in water) was added dropwise to raise the pH to ~8.5. The aqueous dispersion was filtered sequentially through stainless steel screens with pore sizes of 150 pm and 40 pm. The final aqueous particle dispersion had a solids content of 44.3% (theoretical = 53.0%), a z-average particle size of 135 nm as determined by DLS, a final polymer gel level of 0.80 wt% (based on monomers; total gel collected at each mesh size), and a suspension polymer (based on monomers) of 2.69 wt% as determined by Accusizer characterization. The residual MD'M-ALMA level in the serum phase was determined to be 13,700 ppm by UHPLC. TM X-100 polyethylene glycol tert-octylphenyl ether (Dow or its affiliates’ trademark, 0.80 g), and sodium bicarbonate (NaHCO3; 0.40 g) were added to the flask. The contents of the reactor were stirred at 100 rpm and heated to 60 °C under N2. In a separate vessel, a ME containing deionized water (48.5 g), SLS (2.14 g, 28.0% aqueous solution), Triton X-100 (1.20 g), BA (BA; 44.8 g), MMA (42.3 g), styrene (10.1 g), and AA (1.9 g) was prepared using an overhead mixer. A portion of the ME (15.1 g) was added to the reactor, followed by APS (0.13 g) in deionized water (10.0 g), and the reactor temperature was increased to 80 °C over 10 min. The remaining ME and APS solution (0.27 g in 20.0 g water) were fed to the reactor simultaneously at a temperature of 80 °C to 81 °C over 4.5 h and 5 h, respectively (i.e., the APS feed continued for 30 min after the ME feed was complete). At the 3 h mark of the feeds, MD'M ALMA was added to the reactor (10.0 g). After the completion of the APS feed, the reactor was then held at 80 °C for an additional 30 min. The reactor was then cooled to room temperature and ammonium hydroxide solution (28% active in water) was added dropwise to raise the pH to ~8.5. The aqueous dispersion was filtered sequentially through stainless steel screens with pore sizes of 150 pm and 40 pm. The final aqueous particle dispersion had a solids content of 44.3% (theoretical = 53.0%), a z-average particle size of 135 nm as determined by DLS, a final polymer gel level of 0.80 wt% (based on monomers; total gel collected at each mesh size), and a suspension polymer (based on monomers) of 2.69 wt% as determined by Accusizer characterization. The residual MD'M-ALMA level in the serum phase was determined to be 13,700 ppm by UHPLC.

[0085] Comparative Example 4 - Aqueous dispersion of hybrid copolymer particles prepared by the Zhang method

[0086] The method of preparing a hybrid particle aqueous dispersion as described by Zhang, B. et al. (Appl. Surf. Sci. 2007, 254, 452-458) was reproduced. Deionized water (60.0 g), sodium dodecylbenzenesulfonate (0.30 g), and Span 20 sorbitan monolaurate (0.50 g) were added to a 100 mL glass reactor equipped with a condenser, overhead stirrer, and thermocouple. The reactor contents were stirred at 100 rpm, heated to 80 °C, and sparged with N2for 30 min. In a separate vessel, a monomer mixture consisting of MMA (12.0 g), BA (12.0 g), and MD’M-ALMA (1.2 g) was prepared. The monomer mixture and APS solution (0.05 g in 10.0 g water) were simultaneously fed into the reactor over 120 min at a temperature of 80-81 °C. After the feed was complete, the reactor was then held at 80-81 °C for an additional 6 hours. The reactor was then cooled to room temperature, then ammonium hydroxide solution (28% active in water) was added dropwise to raise the pH to ~7.0. The final aqueous particle dispersion had: 22.8% (theoretical = 27.1%) solids, a z-average particle size of 64 nm as determined by DLS, a final polymer gel level of 1.97 wt% (based on monomers; sum of gels collected on each size fraction), and a suspended polymer of 0.66 wt% (based on monomers) as determined by Accusizer characterization. The residual MD’M-ALMA level in the serum phase was determined to be 13,700 ppm by UHPLC.

[0087] Table 1 shows the type and corresponding mass of surfactant added to the monomer emulsion (ME) and / or kettle; the amount of unreacted residual siloxane-acrylate monomer (final MD’M-ALMA); the concentration of suspended copolymer particles formed with diameters >1 pm and <40 pm (ppm susp polymer) (based on monomers); the concentration of gel formed (ppm gel) (based on monomers); and the sum of the concentrations of gel and suspended copolymer particles expressed as a weight percent based on monomers (% susp + gel). ND indicates that the amount of monomer was not detected above the 30 ppm (limit of detection). The percentages of starting materials in the monomer emulsion (ME) and kettle are based on the weight of monomers. The table shows the critical state in the method using both non-ionic and anionic surfactants to reduce gel formation and improve conversion of the siloxane acrylate monomer MD’M-ALMA.

[0088] Table 1 - Residual monomer, suspended polymer and gel formation in emulsion polymerization reactions

[0089]

[0090] The data demonstrate that high concentrations of siloxane-acrylate monomers can be incorporated into copolymer particles with relatively low gel formation and low residual monomer.

Claims

1. A method of making an aqueous dispersion of acrylate-siloxane copolymer particles, the method comprising the steps of: 1) adding a first portion of an aqueous monomer emulsion to a vessel containing water and an anionic surfactant, wherein the contents of the vessel are stirred and controlled at a temperature in the range of 60 °C to 95 °C; 2) adding a first portion of an initiator to the vessel to form an aqueous dispersion of seed copolymer particles over time; then 3) adding a second portion of the monomer emulsion and a second portion of the initiator to the vessel; then 4) maintaining the temperature of the contents of the vessel in the range of 60 °C to 95 °C for a time sufficient to achieve substantially complete conversion of monomers in the monomer emulsion to polymer particles comprising structural units of the monomers to form the aqueous dispersion of acrylate-siloxane copolymer particles; wherein the monomer emulsion has an average monomer droplet size in the range of 1 pm to 30 pm and comprises, based on the total weight of monomers, a) 40 wt% to 98.8 wt% of acrylate monomers; b) 0.1 wt% to 5 wt% of acid monomers; c) 1 wt% to 59.8 wt% of siloxane acrylate monomers; the aqueous dispersion of acrylate-siloxane copolymer particles comprises, based on the total weight of monomers, 0.5 wt% to 5 wt% of non-ionic surfactant; and 0.5 wt% to 5 wt% of anionic surfactant; wherein the siloxane acrylate monomers are represented by Formula I: wherein R is H or CH3; R 1 is H or CH3; Each R 2 It can be independently CH3 or O-Si(CH3)3; Y is -CH2- or -CH2CH2-; and x is 0 or 1 ; provided that when x is 1, R 1 is H; when Y is -CH2-, R 1 is H; and when Y is -CH2CH2-, R 1 is CH3and x is 0; wherein the non-ionic surfactant is represented by Formula II: wherein n is 0 to 10; p is 2 to 30, with the proviso that p > n; and R 3 is a linear or branched C3-C 16 alkyl group; and wherein the anionic surfactant is represented by Formula III: wherein R 4 is C6-C 20 alkyl; m is 0 to 10; and M is Li, Na, or K.

2. The method of claim 1, wherein the siloxane acrylate monomers are:

3. The method of claim 2, wherein n is in the range of 0 to 5 and p is in the range of 3 to 16; the anionic surfactant of Formula III is a linear C 10 -C 14 alkyl sulfate, wherein m is 0; and wherein the weight percent of structural units of the siloxane-acrylate monomer based on the weight of the copolymer particles is in the range of 20 wt% to 55 wt%.

4. The method of claim 3, wherein the acrylate monomers are butyl acrylate and methyl methacrylate, and the acid monomer is methacrylic acid; wherein the weight ratio of butyl acrylate to methyl methacrylate is in the range of 45:55 to 55:45; and wherein the weight ratio of butyl acrylate and methyl methacrylate to methacrylic acid is in the range of 99.5:0.5 to 97:

3.

5. The method of claim 4, wherein the concentration of the non-ionic surfactant of Formula II and the anionic surfactant of Formula III, each, is in the range of 1 wt% to 3 wt% based on the weight of the monomers; wherein the weight ratio of the non-ionic surfactant to the anionic surfactant is in the range of 1:2 to 2:1, wherein the non-ionic surfactant is: wherein p is 3, 8, or 11.

6. The method of claim 5, wherein the non-ionic surfactant is represented by: the anionic surfactant is sodium lauryl sulfate; and the siloxane-acrylate monomer of Formula I is 7. The process of claim 1, wherein in step 1) the vessel containing water and the anionic surfactant of Formula III further contains a non-ionic surfactant of Formula II; wherein the contents of the vessel are stirred and controlled at a temperature in the range of 80°C to 95°C.

8. The process of claim 7, wherein after step 4) a redox initiator package is added to the vessel.

9. The process of claim 7, wherein after step 4) a redox initiator package is added to the vessel, followed by the addition of a neutralizer.

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