PREPARATION OF AN AQUEOUS DISPERSION OF OCCLUDED POLYMERIC PARTICLES

Abstract

The present invention relates to a process for preparing a multiphase occluded aqueous polymer particle dispersion comprising the steps of a) contacting, under emulsion polymerization conditions, first monomers and a chain transfer agent to form an aqueous dispersion of first polymer particles having a Tg in the range of -30 °C to 30 °C; then b) contacting the aqueous dispersion of first polymer particles with a second monomer under emulsion polymerization conditions to form an aqueous dispersion of second polymer particles occluded within the first polymer particles, wherein the first monomer is a phosphorous acid monomer or a salt thereof; and the second monomer comprises at least 90 percent by weight of methyl methacrylate.The aqueous dispersion of occluded polymer particles arising from the process of the present invention is useful in a formulation that can be used to prepare a bubble-free, water-resistant LASD coating.

Description

PREPARATION OF AN AQUEOUS DISPERSION OF OCCLUDED POLYMERIC PARTICLES BACKGROUND OF THE INVENTION Damping materials are used to mitigate vibration in rigid structures in order to reduce noise. In motor vehicles, two main vibration damping technologies predominate: bitumen plates and liquid-applied acoustic damping (LASD) coatings derived from water-based latex. Bitumen plates, a low-cost alternative widely used in the 20th century, exhibit relatively poor damping performance and require laborious manual application. On the other hand, LASD coatings have gained a significant market share because they can be applied quickly using robotic spraying techniques. Furthermore, LASD coatings exhibit better damping properties, environmental, health, and safety (EH&S) profiles, and lower densities.Taken together, these benefits have led automotive OEMs to increasingly use LASD for noise, vibration, and harshness (NVH) management compared to traditional bitumen plates. WO 2018 / 062546 A1 describes aqueous dispersions of polymeric particles suitable for damping applications. Ref. 335046 vibrations. Although improved bubble suppression is reported, water resistance is not described. There is still a need in the art to develop LASD coatings with excellent water resistance compared to bitumen plates. Water-resistant LASD coatings would likely facilitate the adoption of this technology by customers. Furthermore, improved water resistance could allow the use of LASD coatings in new application areas, such as within vehicle wheel wells. Therefore, it would be an advance in the art to develop an aqueous dispersion of polymer particles that can be formulated into a LASD coating that is water-resistant, exhibits an excellent appearance, and maintains high vibration damping performance. BRIEF DESCRIPTION OF THE INVENTION The present invention is a process for preparing a multiphase occluded aqueous polymer particle dispersion comprising the steps of a) contacting, under emulsion polymerization conditions, first monomers and a chain transfer agent to form an aqueous dispersion of first polymer particles having a Tgen in the range of -30 °C to 30 °C, wherein the concentration of the chain transfer agent is from 0.5 to 1.5 percent mol based on moles of the first monomers and the chain transfer agent; then, b) contacting the aqueous dispersion of first polymer particles with a second monomer under emulsion polymerization conditions to form an aqueous dispersion of second polymer particles occluded within the first polymer particles, wherein the first monomers comprise from 0.2 to 5 percent by weight of a phosphorous acid monomer or a salt thereof, based on the weight of the first monomers; the second monomer comprising at least 90 percent by weight of methyl methacrylate; and wherein the weight-to-weight ratio of the first monomers to the second monomer is in the range of more than 80:20 and less than 95:5. The present invention addresses a need in the art by providing an aqueous composition that forms a bubble-free, water-resistant coating that is useful in acoustic damping applications. DETAILED DESCRIPTION OF THE INVENTION The present invention is a process for preparing a multiphase occluded aqueous polymer particle dispersion comprising the steps of a) contacting, under emulsion polymerization conditions, first monomers and a chain transfer agent to form an aqueous dispersion of first polymer particles having a Tgen in the range of -30 °C to 30 °C, wherein the concentration of the chain transfer agent is from 0.5 to 1.5 percent mol based on moles of the first monomers and the chain transfer agent; then, b) contacting the aqueous dispersion of first polymer particles with a second monomer under emulsion polymerization conditions to form an aqueous dispersion of second polymer particles occluded within the first polymer particles, wherein the first monomers comprise from 0.2 to 5 percent by weight of a phosphorous acid monomer or a salt thereof, based on the weight of the first monomers; the second monomer comprising at least 90 percent by weight of methyl methacrylate; and wherein the weight-to-weight ratio of the first monomers to the second monomer is in the range of more than 80:20 and less than 95:5. The first polymer particles are advantageously prepared by contacting first monomers and a chain transfer agent under emulsion polymerization conditions to form an aqueous dispersion of first polymer particles having a Tg, as calculated by the Fox equation, in the range of -30 °C, preferably -20 °C to 30 °C, preferably 20 °C, most preferably 10 °C, wherein the concentration of the chain transfer agent is 0.5, preferably 0.7, most preferably 1 mol percent to 1.5, preferably 1.3 and most preferably 1.2 mol percent based on mol of the first monomers and the chain transfer agent. A chain transfer agent is any compound capable of regulating the molecular weight of the polymer during the polymerization process. Particularly suitable chain transfer agents include alkyl mercaptans, such as n-dodecyl mercaptan (n-DDM) and t-dodecyl mercaptan (t-DDM). As used herein, first monomers refers to monomers selected to form first polymeric particles having a Tgen in the range of -30 °C to 30 °C. The preferred first monomers comprise (a) methyl methacrylate (MMA) or styrene; and (b) one or more monomers selected from the group consisting of butyl acrylate (BA), ethyl acrylate, 2-ethylhexyl acrylate, and 2-propylheptyl acrylate, with the combination of MMA and BA being preferred. The first monomers also comprise 0.2, more preferably 0.5, more preferably 0.8, and most preferably 1.0 percent by weight to 5, more preferably 3, and most preferably 2 percent by weight of structural units of a phosphorous acid monomer or a salt thereof, based on the weight of the first polymeric particles.Examples of suitable phosphorous acid monomers include phosphonates and dihydrogen phosphate esters of an alcohol in which the alcohol contains or is substituted with a polymerizable vinyl or olefinic group. Preferred dihydrogen phosphate esters are hydroxyalkyl(meth)acrylate phosphates, including phosphoethyl methacrylate and phosphopropyl methacrylates, of which phosphoethyl methacrylate is especially preferred. Phosphoethyl methacrylate (PEM) is used herein to refer to the following structure: either II° I^OR OH where R is H oo where the dotted line represents the point of attachment to the oxygen atom. The second polymer particles are advantageously prepared in a second step, after the substantial or complete polymerization of the first monomers, by contacting the aqueous dispersion of the first polymer particles with the second monomer under emulsion polymerization conditions. The second monomer preferably comprises at least 92, more preferably at least 95, more preferably at least 98, and more preferably at least 99 percent by weight of methyl methacrylate. The second monomer may comprise up to 8 percent by weight of another monomer such as methacrylic acid (MAA). The first and second monomers form structural units after polymerization. As used herein, a named monomer structural unit refers to the monomer remnant after polymerization. For example, a structural unit of MMA is as illustrated: EITHER ML / a / ZUZZ / UU l ¿AJ MMA structural unit where the dotted lines represent the attachment points of the structural unit to the polymer backbone. The resulting second Tgalta polymer particles form distinct (hard) Tgalta domains within the first Tgbaja (soft) domain polymer particles, as opposed to the formation of a distinct outer layer overlaid on the Tgbaja polymer particles as described in WO 2018 / 062546 A1. The distinct domains are said to be occluded (embedded) in the first polymer particles. The occlusion was confirmed by atomic force microscopy. A discussion and description of the morphology of occluded multiphase latex particles can be found in J. Coat. Technol. Res., 5 (2) 169-180, 2008. The weight-to-weight ratio of the second polymer particles occluded to the first polymer particles is preferably in the range of 6:94, with greater preference from 8:92 to 19:81, with greater preference to 17:83. The occluded polymer particles preferably have an average particle size z, as determined by dynamic light scattering, in the range of 80 nm, with a higher preference for 100 nm to 400 nm, with a higher preference for 300 nm, and with a higher preference for 200 nm. The polymer particles preferably have a Mn (measured by gel permeation chromatography described below) in the range of 10,000 g / mol, with a higher preference for 11,000 g / mol, preferably 22,000 g / mol, with a higher preference for 18,000 g / mol, with a higher preference for 15,000 g / mol, and with a higher preference for 13,000 g / mol. The solids content of the aqueous dispersion of occluded multiphase polymer particles is preferably in the range of 20 to 60 percent by weight. Preferably, the multiphase polymer particles are two-phase polymer particles. The aqueous dispersion of occluded polymer particles is advantageously used as part of a formulation suitable for LASD applications. The formulation comprises at least one additive selected from the group consisting of extenders, baking additives such as starches, and rheology modifiers. Preferably, the formulation comprises all of these additives. The formulation also preferably comprises a non-ionic compound of Structure I: Yo ML / a / ZUZZ / UU l ¿Au where R1 is H or Ce-Cis alkyl; R2 is H or CH3; and x is 30, preferably 45 and more preferably 80; to 300, preferably 250 and more preferably 200. The preferred nonionic compounds are polyethylene glycols (where R1 is H) or polyethylene oxide secondary alcohol ethoxylates (where R1 is a branched alkyl group). Suitable commercially available nonionic compounds include CARBOWAX™ polyethylene glycols PEG 4000 and 8000 (PEG 4000 and PEG 8000, respectively) and TERGITOL™ secondary alcohol ethoxylates 15-S-20 and 15-S-40 (Trademarks of The Dow Chemical Company or its affiliates). The concentration of the non-ionic compound of the structure And in the formulation is in the range of 0.2, with the highest preference at 0.5 percent by weight to 5, with the highest preference at 3 and with the highest preference at 2 percent by weight, based on the weight of the formulation. It has been found that phosphorous acid functionalization, preferably PEM functionalization, of the soft domain of occluded polymer particles has a particularly beneficial effect on the texture, bubble formation, and water uptake profiles of formulations comprising these occluded polymer particles with respect to the prescribed narrow Mn range; furthermore, it has been found that the inclusion of the non-ionic compound of Structure I in the formulation together with the phosphorous acid-functionalized occluded polymer particles improves these critical properties. Surprisingly, it has been discovered that coatings suitable for vibration damping applications can be prepared with a desirable texture, very little water uptake, as well as little or no evidence of bubble formation. Gel permeation chromatographic method for measuring the Mnde of occluded particles The GPC samples were prepared in THE at a concentration of 5 mg / ml based on the occluded polymeric solids content. The sample solutions were maintained ML / a / ZUZZ / UU l Z4 J were incubated on a platform shaker at room temperature overnight, then filtered through a 0.45 pm PTFE filter (Whatman) prior to GPC analysis. The GPC instrument setup consisted of an Agilent 1200 series HPLC system (degasser, pump, autosampler) and a Wyatt T-rEX refractive index detector. Polymer separation was performed on a column array consisting of one TOSOH TSKgel GMHxi-L column and one TOSOH TSKgel G5000Hxi column (each packed with 9 pm styrene divinylbenzene gels; each dimension 7.5 mm ID x 30 cm) with THF as the mobile phase at a flow rate of 1 ml / min; the injection volume was 40 pL. Astra 7 software (Wyatt Technology) was used for data acquisition and processing. Mny Mwse were calculated using a conventional calibration method based on polystyrene standards (Agilent Technology) as shown in Table 1 below: Table 1 - Polystyrene Standard ML / a / ZUZZ / UU l ¿AJ Peak PS Al Mixture (g / mol) PS B1 Mixture (g / mol) 1 6,035,000 2,698,000 2 597,500 290,300 3 126,000 69,650 4 30,230 9,960 5 2,970 580 The weighted average and number molecular weights were obtained based on the polystyrene calibration curve and sample elution profile using the following equations: M =-nΣ^=M^ Σ^μ^M™ = y / Vh¿i=l “i Where hi is the height of the GPC curve at the i-th volume increment and Mi is the molecular weight of the eluted species at the i-th retention volume based on the polystyrene calibration curve. Examples Example 1 - Preparation of an aqueous dispersion of occluded polymer particles in 2 stages with 10% hard stage A first monomeric emulsion was prepared by mixing deionized water (492 g), sodium lauryl ether sulfate (43 g, 31% active in water), BA (1066 g, 8.32 mol), MMA (797 g, 7.96 mol), PEM (43 g, 60% active, 0.12 mol) and n-DDM (37 g, 0.18 mol). A second monomeric emulsion was prepared by mixing deionized water (134 g), sodium lauryl ether sulfate (5 g, 30% active in water) and MMA (214 g, 2.14 mol). Deionized water (881 g) and sodium lauryl ether sulfate (2.4 g, 31% active) were added to a 5 L four-necked round-bottom flask equipped with a paddle stirrer, thermometer, nitrogen inlet, and reflux condenser. The flask contents were heated to 84 °C under nitrogen, and stirring was initiated. A portion of the first monomeric emulsion (132 g) was then rapidly added, followed by the addition of ammonium persulfate solution (5 g) in deionized water (55 g). After stirring for 10 min, the remainder of the first monomeric emulsion and an ammonium persulfate starter solution (2.1 g) in deionized water (90 g) were added separately over 80 min. The contents of the flask were kept at 84 °C for 10 min, after which the second monomeric emulsion and a starter solution containing sodium persulfate (0.2 g) in deionized water (10 g) were added separately to the flask for a period of 10 min. The batch was then cooled, and the residual monomer was reduced with a redox couple and subsequently neutralized to pH 9. The average particle size z, measured using a Brookhaven BI-90 Plus particle size analyzer, was 165 nm, and the percentage of solids was found to be 51%. The calculated gel permeation microchromatographic density was found to be 12,000 g / mol. Example 2 - Preparation of an aqueous dispersion of occluded polymer particles in 2 stages with 15% hard stage The process described in Example 1 was followed, except that the relative amounts of monomeric emulsion 1 and monomeric emulsion 2 were adjusted to a weight-to-weight ratio of 85:15. The measured average particle size z was 160 nm and the percentage of solids was found to be 51%. The calculated gel permeation monochromatographic density was found to be 12,000 g / mol. Example 3 - Preparation of an aqueous dispersion of occluded polymer particles in 2 stages with 10% hard stage of MMA / MAA The process described in Example 1 was followed, except that 1.5 wt% of the MMA (3.2 g) was replaced with an equal amount (3.2 g) of MAA in the second monomeric emulsion. The measured average particle size z was 163 nm, and the percentage of solids was found to be 52%. The calculated gel permeation chromatographic Mn was found to be 12,000 g / mol. Example 4 - Preparation of an aqueous dispersion of occluded polymer particles in 2 stages with a lower concentration of the chain transfer agent The process described in Example 1 was repeated, except that the amount of n-DDM in the first monomeric emulsion was reduced from 37 g to 18.5 g (0.09 mol). The measured particle size was 168 nm and the percentage of solids was found to be 51%. The calculated gel permeation chromatographic density was found to be 20,000 g / mol. Example 5 - Preparation of an aqueous dispersion of ML / a / ZUZZ / UU l ¿Au polymeric particles occluded in 2 stages with a lower concentration of the chain transfer agent The process described in Example 1 was repeated, except that the amount of n-DDM in the first monomer emulsion was reduced from 37 g to 29 g (0.14 mol). The average particle size z measured was 175 nm and the percentage of solids was found to be 51%. The calculated gel permeation chromatographic Mn was found to be 15,000 g / mol. Example 6 - Preparation of an aqueous dispersion of occluded polymer particles in 2 stages with a higher concentration of the chain transfer agent The process described in Example 1 was repeated, except that the amount of n-DDM in the first monomer emulsion was increased from 37 g to 48 g (0.24 mol). The average particle size z measured was 192 nm, and the percentage of solids was found to be 51%. The calculated gel permeation chromatographic density was found to be 10,000 g / mol. Example 7 - Preparation of a 2-step occluded polymer with MMA and BA in the hard domain The process was followed as described in Example 1, except that the monomer composition of the second monomeric emulsion was BA (10.7 g) and MMA (203.3 g) instead of all MMA. The average particle size z found was 170 nm, and the percentage of solids was found to be 51%. The gel permeation chromatography was found to be ΜΛ / a / ZUZZ / UU l Z4 J calculated was 12,000 g / mol. Comparative Example 1 - Preparation of an aqueous dispersion of occluded polymer particles in 2 stages with a lower concentration of the chain transfer agent The process described in Example 1 was repeated, except that the amount of n-DDM in the first monomer emulsion was reduced from 37 g to 9.6 g (0.05 mol). The measured average particle size z was 167 nm, and the percentage of solids was found to be 51%. The calculated gel permeation chromatographic density was found to be 34,000 g / mol. Comparative Example 2 - Preparation of an aqueous dispersion of occluded polymer particles in 2 stages with a higher concentration of the chain transfer agent The process described in Example 1 was repeated, except that the amount of n-DDM in the first monomer emulsion was increased from 37 g to 57 g (0.28 mol). The average particle size z measured was 164 nm, and the percentage of solids was found to be 52%. The calculated gel permeation chromatography strength was found to be 8600 g / mol. Comparative Example 3 - Preparation of an aqueous dispersion of occluded polymer particles in 2 stages with 10% hard domain of MMA and isobornyl methacrylate The process as described in Example 1 was repeated except that isobornyl methacrylate (106 g) replaced a ML / a / ZUZZ / UU l ¿AJ equal amount of MMA (106 g) in the second monomeric emulsion. The average particle size z measured was 164 nm and the percentage of solids was found to be 51%. The calculated gel permeation chromatographic Mn was found to be 12,000 g / mol. Comparative Example 4 - Preparation of an aqueous dispersion of occluded polymer particles in 2 stages with 10% styrene hard domain The process as described in Example 1 was repeated except that styrene (214 g) was used in the second monomeric emulsion instead of MMA, and the feed time for the second monomeric emulsion was 30 min. The measured average particle size z was 163 nm, and the percentage of solids was found to be 51%. The calculated gel permeation chromatographic Mn was found to be 13,000 g / mol. Preparation of coating formulations The coating formulations were prepared from the components listed in Table 2 in the order listed. The components were mixed with an overhead mixer for 10 min, then allowed to equilibrate overnight. Emulsion polymer refers to the aqueous dispersions of occluded polymer particles from Examples 1-7 and Comparative Examples 1-5. Table 2 - Coating formulation Component Mass (g) Emulsion polymer 39.2 Pigment Bayferrox Black 318 0.2 Durcal 10 CaCOa 57.9 Potato starch Kollotex 1500 2.5 Rheology modifier ACRYSOL™ RM-12W 1.0 Polyethylene glycol CARBOWAX™ PEG 8000a 1.0 Only Formulations 4-7 and Comparative Formulations 1 and 2 include PEG 8000 (see Table 2). Water intake test The coatings were stretched onto four 100 x 80 mm samples on aluminum panels. The samples were then left at room temperature for 30 minutes and subsequently baked at 150 °C for 30 minutes. The samples were cooled to room temperature and weighed to determine their total mass. The samples were then immersed in 10 cm of water for 48 minutes and weighed again. Water uptake was reported as the percentage difference in mass between the soaked and unsoaked samples. Bubble formation Bubble formation was evaluated on a scale of 1-10 as defined below: 10: Traces or no surface defects: Small bumps: Moderate bumps: Large bumps: Huge bumps Texture The texture was evaluated on a scale of 1-10 as defined below: ML / a / ZUZZ / UU l Z4 J 10: Traces or no defects on the surface 8: Craters, small boreholes 6: Craters, moderate boreholes 4: Craters, large boreholes 2: Craters, enormous boreholes Table 3 summarizes the results of water uptake, bubble formation and texture for coatings prepared from the formulations. Table 3 - Water uptake, bubble formation and coating texture Formulation No. Example No. Texture Bubble Formation Water Absorption 48 h (%) 1 Ex · 1 10 10 5.2 2 Ex · 2 9 10 4.8 3 Ex · 3 9 10 3.7 4 Ex · 4 10 10 7.9 5 Ex · 5 10 10 4.6 6 Ex. 6 8 10 3.4 7 Ex. 1 10 10 3.0 8 Ex. 7 10 9 4.9 Comp. 1 Ex · comparative 1 9 3 11.0 Comp. 2 Ex · comparative 2 6 6 3.4 Comp. 3 Ex · comparative 3 3 6 2.3 Comp. 4 Ex · comparative 4 5 6 2.7 MA / a / 4U44 / UU 1444 All coatings formed from the compositions in Examples 1–7 exhibit excellent appearance with no major defects, as demonstrated by numerical ratings for texture and bubble formation of at least 8. Furthermore, each coating in Examples 1–7 has acceptable water uptake of less than 10%. In contrast, all compositions in the comparative examples fail in at least one aspect of appearance. The results highlight the critical role of Mnasí as the weight-high fraction of MMA structural units in the second occluded polymer. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

CLAIMS Having described the invention as above, the following claims are claimed as property:

1. A process for preparing an aqueous dispersion of multiphase occluded polymer particles, characterized in that it comprises the steps of a) contacting, under emulsion polymerization conditions, first monomers and a chain transfer agent to form an aqueous dispersion of first polymer particles having a Tg in the range of -30 °C to 30 °C, wherein the concentration of the chain transfer agent is from 0.5 to 1.5 percent by mole based on the mole of the first monomers and the chain transfer agent; then b) contacting the aqueous dispersion of first polymer particles with a second monomer under emulsion polymerization conditions to form an aqueous dispersion of second polymer particles occluded within the first polymer particles, wherein the first monomers comprise from 0.2 to 5 percent by weight of a phosphorous acid monomer or a salt thereof, based on the weight of the first monomers; the second monomer comprises at least 90 percent by weight of methyl methacrylate; and wherein the weight-to-weight ratio of the first monomers to the second monomer is in the range of more than 80:20 and less than 95:

5.

2. The process according to claim 1, characterized in that the first monomers comprise a) methyl methacrylate or styrene; and b) one or more monomers selected from the group consisting of butyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, and 2-propylheptyl acrylate.

3. The process according to claim 2, characterized in that the phosphorous acid monomer is phosphoethyl methacrylate at a concentration of 0.5 to 3 percent by weight, based on the weight of the first monomers.

4. The process according to claim 3, characterized in that the second monomer comprises at least 95 percent by weight of methyl methacrylate, and the weight-to-weight ratio of the second monomer to the first monomers is in the range of 8:92 to 17:

83.

5. The process according to claim 4, characterized in that the concentration of the chain transfer agent is in the range of 0.7 to 1.3 percent by mol, based on mol of first monomers and of the chain transfer agent.

6. The process according to claim 5, characterized in that the first monomers comprise methyl methacrylate, butyl acrylate, and phosphoethyl methacrylate; and wherein the second monomers comprise at least 98 percent by weight of methyl methacrylate.