Alkali-soluble resin (ASR) shell epoxy RDP exhibiting improved shelf stability

Abstract

The present invention provides shelf stable redispersible multilayer polymer particles (RDPs) comprising a major proportion of epoxy resins, a methacrylic acid or anhydride containing alkali soluble polymer outer layer and a hydrophobic chain transfer agent or a high glass transition temperature colloidal stabilizer, such as poly(vinyl pyrrolidinone) or its copolymer, as well as to methods of making the same.

Claims

1. A redispersible polymer powder composition comprising as powder or an aqueous dispersion multilayer polymer particles of from 50 to 90 wt. % of epoxy resin compositions having a calculated glass transition temperature (Tg) of from 0 to 40° C., and from 10 to 50 wt. %, of an alkali soluble polymer shell around the epoxy resin, which polymer shell is the copolymerized product of from 10 to 50 wt. % of methacrylic acid or its anhydride, based on total weight of monomers copolymerized to form the alkali soluble polymer shell, and the remainder of one or more ethylenically unsaturated comonomer and, if included, one or more chain transfer agent, wherein in the redispersible polymer powder, (i) the alkali soluble polymer comprises in copolymerized form from 0.1 to 10 wt. %, based on total weight of monomers copolymerized to form the alkali soluble polymer shell plus chain transfer agents, of one or more hydrophobic chain transfer agent, (ii) the redispersible polymer powder comprises from 3 to 25 wt. % based on the total weight of epoxy resin, alkali soluble polymer and colloidal stabilizer solids, of one or of a mixture of colloidal stabilizers having a Tg of 90° C. or more, or (iii) both (i) and (ii).

2. The redispersible polymer powder composition as claimed in claim 1, wherein the calculated Tg of the epoxy resin composition is from 5 to 35° C.

3. The redispersible polymer powder composition as claimed in claim 1, wherein the epoxy resin composition is a blend of two or more epoxy resins.

4. The redispersible polymer powder composition as claimed in claim 1, wherein the alkali soluble polymer that comprises the polymer shell of the multilayer polymer particle has a calculated Tg of 60 to 120° C.

5. The redispersible polymer powder composition as claimed in claim 1, wherein the alkali soluble polymer shell is the copolymerized product of from 20 to 50 wt. % of methacrylic acid or its anhydride, based on total weight of monomers copolymerized to form the alkali soluble polymer.

6. The redispersible polymer powder composition as claimed in claim 1, wherein the chain transfer agent comprises N-dodecyl mercaptan.

7. The redispersible polymer powder composition as claimed in claim 1, wherein the colloidal stabilizer is chosen from poly(vinyl pyrrolidone) or a copolymer thereof.

8. A composition comprising cement or hydraulic binder and the redispersible polymer powder composition as claimed in claim 1.

9. A method for making a water dispersible epoxy multilayer polymer powder comprising: mechanically dispersing an epoxy resin in an aqueous medium to form an initial aqueous epoxy resin dispersion; charging the initial aqueous epoxy resin dispersion into a reaction vessel; providing in the reaction vessel an ethylenically unsaturated monomer mixture comprising (i) from 10 to 50 wt. % of methacrylic acid or its anhydride, and (ii) the remainder of one or more copolymerizable ethylenically unsaturated monomers, each based on the total weight of ethylenically unsaturated monomers copolymerized to form a polymer shell; copolymerizing the monomer mixture in the presence of the initial aqueous epoxy resin dispersion to form an aqueous multilayer polymer particle dispersion; adding one or more colloidal stabilizer to the aqueous multilayer polymer particle dispersion; and, removing the aqueous phase from the resulting multilayer polymer to obtain a water redispersible epoxy polymer powder having an alkali soluble polymer shell, wherein the resulting water redispersible epoxy multilayer polymer powder has from 50 to 90 wt. % of epoxy resin compositions, based on total multilayer polymer particle solids, and, further wherein, the resulting epoxy multilayer polymer powder comprises (i) one or a mixture of colloidal stabilizers having a Tg of 90° C. or more, (ii) from 0.1 to 10 wt. %, based the total weight of ethylenically unsaturated monomers copolymerized to form the polymer shell, of a hydrophobic chain transfer agent in copolymerized form, or both (i) and (ii).

10. The process as claimed in claim 9, wherein the providing the monomer mixture comprises adding the ethylenically unsaturated monomer mixture by gradual addition to the reaction vessel containing the initial aqueous epoxy resin dispersion.

Description

EXAMPLES

(1) The present invention will be illustrated below by the following non-limiting examples.

Example 1: Batch Dispersion

(2) To a stainless steel (300 mL) PARR pressure reactor having a 6.67 cm inside diameter, a Cowles blade stirrer, and equipped with an optional pulley system to allow a mixer speed of up to 1830 rpm was charged 70.0 g of D.E.R. 661 (1-type solid bisphenol-A epoxy resin, Mw=1500 g/mol, epoxy equivalent weight=500-560) or epoxy resin blend of D.E.R. 331 (liquid bisphenol-A epoxy resin, Mw=380 g/mol, EEW=182-192, Dow Chemical, Midland, Mich.) and D.E.R. 669E (9-type solid bisphenol-A epoxy resin, Mw=15000 g/mol, EEW=2500-4000). 25.0 g of MOWIOL 4-88 aqueous solution (Polyvinyl alcohol, 88% hydrolyzed, solid content=28.0 wt. %, Kuraray Europe GmbH,). The Tgs of epoxy resin or blend are shown in Table 1, below. The stirrer assembly was inserted into the vessel and turned by hand until it spun freely. The Parr reactor assembly was then loaded onto its ring stand and water hoses were attached to the stirrer's cooling sleeve. The thermocouples and stirrer motor were connected, and the heating mantle was lifted into place and tightened. The reactor was sealed and heated to 100° C., and after reaching the temperature the mixture was stirred for 10 minutes to allow sufficient mixing of the epoxy resin and PVOH solution together at ˜1830 rpm. To this mixture water was added using a HPLC pump at the rate of 1.4 ml/min for 20 min. The water addition rate was increased to 14 mL/min for 4 min while the heating mantle was removed and the Parr reactor was cooled by air and water. The reactor was cooled down to 50° C. in water bath while stirring. The resultant dispersion was collected by filtration through a 190 μm filter and had a 40-45% solids content.

Example 2: Continuous Extrusion Dispersion Process

(3) The Epoxy Dispersions were prepared using a KWP (KRUPP WERNER & PFLEIDERER Ramsey, N.J.) ZSK25 extruder (60 L/D rotating at 450 rpm) according to the following procedure with the formulation components shown in Table 1, below. The solid epoxy resin (D.E.R. 669E (9-type solid bisphenol-A epoxy resin, Mw=15000 g/mol, EEW=2500-4000) or D.E.R. 667E (7-type solid bisphenol-A epoxy resin, Mw=10000 g/mol, EEW=1600-1950) and the semi-crystalline MOWIOL 488 (Polyvinyl alcohol, 88% hydrolyzed, Kuraray Europe GmbH)) were supplied to the feed throat of the extruder via a Schenck Mechatron loss-in-weight feeder and then melted blended in extruder, and a liquid epoxy stream (D.E.R. 331, liquid bisphenol-A epoxy resin, Mw=380 g/mol, epoxy equivalent weight EEW=182-192) was injected into the melt zone to melt blend with solid epoxy and dispersant before entering the emulsification zone. The initial aqueous stream (IA) was then metered into the emulsification zone, and the melt polymer blend was then emulsified in the presence of water in the extruder. A co-dispersant E-SPERSE 100 (PEO (14) di- and tristyrenated Phenol ammonium sulfate (Ethox Chemicals, LLC Greenville, S.C.)) can be injected into the emulsification zone together with IA. The emulsion phase was then conveyed forward to the dilution and cooling zone of the extruder where additional water was added to form the aqueous dispersions having solid level levels of less than 60 weight percent. The properties of each of the dispersion components were measured, and are reported in Table 1. The initial water and liquid co-dispersants like E-SPERSE 100, and dilution water were all supplied by ISCO dual syringe pumps (500 ml). The barrel temperature of the extruder was set to 100° C. After the dispersion exited the extruder, it was further cooled and filtered via a 200 μm mesh size filter.

(4) TABLE-US-00001 TABLE 1 Epoxy Blend Dispersions (all parts by weight) Epoxy Epoxy Tg Co- Solid wt. % V.sub.mean Dispersion* Epoxy or blend (° C.) Dispersant dispersant in dispersion (μm) A D.E.R. 661 40 Mowiol ™ None 39.18 0.323 (100 part) 488 (10 part) B DER667E/DER331 22 Mowiol ™ E-Sperse 56.94 0.443 (3:2) (101 part) 488 (6.2 part) 100 (2 part) C DER669E/DER331 15 Mowiol ™ E-Sperse 44.97 0.351 (1:1) (101 part) 488 (6.2 part) 100 (2 part) D DER669E/DER331 5 Mowiol ™ None 45.7 0.218 (1:2) (100 part) 488 (10 part) *Dispersions A and D were prepared by batch dispersion process; dispersions B and C were prepared by continuous dispersion process.

(5) Particle Size Analysis (V.sub.mean, Volume-Average Particle Size) for Polymer Dispersions and Redispersions of the RDP Samples:

(6) An epoxy multilayer polymer particle dispersion sample was diluted in de-ionized (DI) water prior to analysis to avoid saturating the detector. Epoxy RDP was dispersed into DI water at 1% solid (at pH=7) and vortexed for 30 seconds twice. In addition, in order to measure the particle size in alkaline condition, 2-3 drops of 1 M NaOH solution was added into the redispersion to raise the pH to >10. Particle size was measured on Beckman Coulter LS 13 320 Laser Light Diffraction Particle Size analyzer (Beckman Coulter, Inc. Brea, Calif.), using an epoxy resin model predetermined by the instrument software. Solid content analysis was performed on an Ohaus MB45 moisture analyzer (Ohaus Corporation, Parsippany, N.J.).

Example 3: Seeded Emulsion Polymerization of Alkali Soluble Polymer Dispersions E, F, G, H, I, J, N and P (Chain Transfer Agent Mixed with Acrylic Monomers for Polymerization)

(7) Procedure A:

(8) Using dispersion E in Table 2, below, as an example, into a round bottom flask was added 113.4 g of the diluted epoxy dispersion A in Table 1 prepared by a batch dispersion process (solid content=40.0 wt. %) and purge with nitrogen gas while maintaining at 60° C. While stirring, 10 mg of ferrous sulfate as 1 wt. % aqueous solution was added into the dispersion. Also, 6.60 grams of methyl methacrylate and 1.65 grams of methacrylic acid were mixed and injected into the reactor over 60 min. At the same time, 2.5 g of a 2.5 wt % aqueous solution of tert-butyl peroxide, and, separately, 2.5 g of 2.5 wt % aqueous solution of sodium hydroxymethanesulfinate (total 0.75 wt. % of each component relative to acrylic monomer weight) were fed into the reactor as free radical initiators over 90 min. The reaction was maintained at 60° C. for 90 min and then allowed to cool to 25° C. and filtered through a 190 μm filter. The dispersion was isolated and analyzed: 40.43% Solids; 340 nm particle size.

(9) Dispersion F was made from dispersion D in Table 1, above, in the same way as Dispersion E (Procedure A, above), except 13.2 grams of methyl methacrylate, 3.30 grams of methacrylic acid, 2.5 g of a 5.0 wt % aqueous solution of tert-butyl peroxide, and, separately, 2.5 g of 5.0 wt. % aqueous solution of sodium hydroxymethanesulfinate (total 0.75 wt. % of each component relative to acrylic monomer weight) were used.

(10) Dispersion G was made from dispersion B in Table 1, above, in the same way as Dispersion E (Procedure A, above), except 8.39 grams of methyl methacrylate, 2.10 grams of methacrylic acid, 2.5 g of a 3.15 wt. % aqueous solution of tert-butyl peroxide, and, separately, 2.5 g of 3.15 wt. % aqueous solution of sodium hydroxymethanesulfinate (total 0.75 wt. % of each component relative to acrylic monomer weight) were used.

(11) Dispersion H was made from dispersion B in Table 1, above, in the same way as Dispersion E (Procedure A, above), except 8.39 grams of methyl methacrylate, 2.10 grams of methacrylic acid, 0.105 gram of n-dodecyl mercaptan, 2.5 g of a 3.15 wt % aqueous solution of tert-butyl peroxide, and, separately, 2.5 g of 3.15 wt % aqueous solution of sodium hydroxymethanesulfinate (total 0.75 wt. % of each component relative to acrylic monomer weight) were used.

(12) Dispersion I was made from dispersion B in Table 1, above, in the same way as Dispersion E (Procedure A, above), except 8.39 grams of methyl methacrylate, 2.10 grams of methacrylic acid, 0.210 gram of n-dodecyl mercaptan, 2.5 g of a 3.15 wt % aqueous solution of tert-butyl peroxide, and, separately, 2.5 g of 3.15 wt % aqueous solution of sodium hydroxymethanesulfinate (total 0.75 wt. % of each component relative to acrylic monomer weight) were used.

(13) Dispersion J was made from dispersion B in Table 1, above, in the same way as Dispersion E (Procedure A, above), except 8.39 grams of methyl methacrylate, 2.10 grams of methacrylic acid, 0.210 gram of methyl 3-mercaptopropionate, 2.5 g of a 3.15 wt % aqueous solution of tert-butyl peroxide, and, separately, 2.5 g of 3.15 wt % aqueous solution of sodium hydroxymethanesulfinate (total 0.75 wt. % of each component relative to acrylic monomer weight) were used.

(14) Dispersion N was made from dispersion C in Table 1, above, in the same way as Dispersion E (Procedure A, above), except 16.78 grams of methyl methacrylate, 4.20 grams of methacrylic acid, 2.5 g of a 6.3 wt % aqueous solution of tert-butyl peroxide, and, separately, 2.5 g of 6.3 wt % aqueous solution of sodium hydroxymethanesulfinate (total 0.75 wt. % of each component relative to acrylic monomer weight) were used.

(15) Dispersion P was made from dispersion C in Table 1, above, in the same way as Dispersion E (Procedure A, above), except 9.06 grams of methyl methacrylate, 3.52 grams of methacrylic acid, 0.503 gram of n-dodecyl mercaptan, 2.5 g of a 3.77 wt % aqueous solution of tert-butyl peroxide, and, separately, 2.5 g of 3.77 wt % aqueous solution of sodium hydroxymethanesulfinate (total 0.75 wt. % of each component relative to acrylic monomer weight) were used.

Example 4: Seeded Emulsion Polymerization of Alkali Soluble Polymer Dispersions K, L, M, O and Q with an Epoxy Seed Dispersion and Emulsion Polymerization of Acrylic Alkali Soluble Polymer Dispersions R and S

(16) Procedure B:

(17) Using hybrid dispersion L in Table 2, below, as an example. At ambient temperature (23° C.), 200 g of an aqueous epoxy dispersion (dispersion C in Table 1, above) and 25 g of DI water were added to a 500 mL, 4-neck round bottom flask equipped with a mechanical stirrer, thermocouple, condenser and a stainless steel dip tube, stirred at 125 rpms, and warmed. The monomer emulsion (ME) indicated in Table 1A was prepared by adding the ingredient listed below by mixing for 10 minutes with a stir bar. When the reactor contents reached 60° C., the promoter solution from Table 1A, below was added quickly in one addition to the reactor followed by the addition of the ME, cofeed initiator and activator solutions (as in Table 1A, below) using Cole-Palmer Dual syringe pumps (Model 200) (from Cole-Parmar Instrument Company, Vernon Hills, Ill.). The ME was feed at 1.73 gm/min (total feed time 30 min). Both of the cofeed solutions were feed at 0.34 gm/min (total feed time 45 min). The temperature of the emulsion was maintained between 59-61° C. The emulsion was continuously stirred with a peak agitation of 300 rpms.

(18) TABLE-US-00002 TABLE 1A Alkali Soluble Polymer Composition for Emulsion Polymerization to make Dispersion L Wt (gm) Monomer Emulsion (ME) DI Water 11.5 Sodium Dodecylbenzene 0.14 Sulfonate Methyl Methacrylate 30.49 (MMA) Allyl Methacrylate 0.59 Methacrylic Acid (MAA) 7.77 n-Dodecyl Mercaptan 1.48 (NDDM) Cofeed Initiator t-Butyl 0.41 Hydroperoxide (70%) DI Water 15 Co-feed Activator Sodium 0.27 Formaldehyde Sulfoxylate DI Water 15 Promoter Iron (II) Sulfate 0.002 Heptahydrate DI Water 5 Chase Initiator t-Butyl 0.05 Hydroperoxide (70%) DI Water 5 Chase Activator Sodium 0.05 Formaldehyde Sulfoxylate DI Water 5

(19) After the feeds in Table 1A, above, were completed, both the chase initiator and activator solutions were sequentially added to the reactor in one quick addition. The reactor contents were then maintained at 60° C. for 15 minutes. After this time, the reactor contents were cooled to ambient temperature (<30° C.). The latex was isolated and analyzed: 40.43% Solids; 414 nm particle size, 75 ppm MMA and pH 3.51.

(20) Dispersion K was made from dispersion C in Table 1, above, in the same way as Dispersion L (Procedure B and Table 1A, above), except using 66.7 wt. % of each the feeds listed in Table 1A, above, based on the weight of each respective feed in Table 1A.

(21) Dispersion M was made from dispersion C in Table 1, above, in the same way as Dispersion L (Procedure B and Table 1A, above), except using 166.7 wt. % of each of the feeds listed in Table 1A, above, based on the weight of each respective feed in Table 1A.

(22) Dispersion O was made from dispersion C in Table 1, above, in the same way as Dispersion L (Procedure B and Table 1A, above), except using 32.52 grams of MMA and 5.74 grams of MAA.

(23) Dispersion Q was made from dispersion C in Table 1, above, in the same way as Dispersion L (Procedure B and Table 1A, above), except replacing MAA with acrylic acid (AA).

(24) Dispersion R was made in the same way as Dispersion L (Procedure B and Table 1A, above), except replacing the seed epoxy dispersion with 5.11 grams of Mowiol™ 488 and 2.75 grams of E-Sperse 100 (60% active).

(25) Dispersion S was made in the same way as Dispersion L (Procedure B and Table 1A, above), except replacing the seed epoxy dispersion with 5.11 grams of Mowiol™ 488 and 2.75 grams of E-Sperse 100 (60% active) and without adding nDDM.

(26) The effect of chain transfer agent on the molecular weight of the alkali soluble polymeras shown in Table 3, below, on the molecular weight of the emulsion polymers of Dispersions R and S was characterized by size exclusion chromatography (SEC) based on polystyrene standards. By adding 4% nDDM, the molecular weight of the alkaline soluble polymer was significantly reduced.

(27) TABLE-US-00003 Alkali Soluble Particle Polymer Composition % Solids Size pH Mn R 30% ASR, 4% 39.18% 355 nm 3.93 14.4k nDDM S 30% ASR, no 40.43% 414 nm 3.51 36.1k nDDM *Alkali Soluble Resin (ASR) contains 78.5 wt. % PMMA and 20 wt. % PMAA, and 1.5 wt. % ALMA, based on the total weight of monomers used to make the resin; nDDm is n-dodecyl mercaptan.

(28) TABLE-US-00004 TABLE 2 Summary of Multilayer Polymer Particle Dispersions Multilayer Alkali Soluble Polymer Particle Epoxy Polymer Shell (wt. V.sub.mean Dispersion Dispersion parts phr epoxy) (nm) E A PMMA-PMAA (4:1) 340 20 part F D PMMA-PMAA (4:1) 240 40 part G B PMMA-PMAA (4:1) 458 25 part H B PMMA-PMAA (4:1) 370 25 part 1% nDDM I B PMMA-PMAA (4:1) 370 25 part 2% nDDM J B PMMA-PMAA (4:1) 368 25 part 2% MMP K C 20% ASR 4% 355 nDDM (MMA:MAA = 4:1) L C 30% ASR 4% nDDM 365 (MMA:MAA = 4:1) M C 50% ASR 4% 374 nDDM (MMA:MAA = 4:1) N C 50% ASR 380 (MMA:MAA = 4:1) O C 30% ASR 4% nDDM 368 (MMA:MAA = 17:3) P C 30% ASR 4% nDDM 360 (MMA:MAA = 18:7) Q C 30% ASR 4% nDDM 368 (MMA:AA = 4:1) nDDM: n-dodecyl mercaptan; MMP: Methyl 3-mercaptopropionate; phr: per hundred weight parts resin solids; In dispersions K, L, M and O, there is 1.5 wt. % ALMA in ASR shell, based on the total weight of monomers used to make the resin.

Example 4: Spray Drying to Make RDPs

(29) A two-fluid nozzle atomizer was equipped on a MOBILE MINOR™ 2000 Model H spray dryer (GEA Niro, Denmark). The nitrogen pressure to nozzle atomizer was fixed at 1 bar with 50% flow which is equivalent to 6.0 kg/hour of air flow. A glass jar was placed under the cyclone with the valve on the bottom of the cyclone open. Each of the aqueous dispersions from Table 2, above, (35-40 wt. % solid content) was pumped into the nozzle atomizer by an emulsion feed pump (from Cole-Parmar Instrument Company, Vernon Hills, Ill.). Where indicated in Table 3, below, additional polymer stabilizer like PVOH and polyvinylpyrrolidone (PVP) was mixed into the dispersion prior to spray drying. The spray drying experiment was conducted in N.sub.2 environment with an inlet temperature fixed at 140° C., and the outlet temperature was targeted at 50° C. by tuning the feed rate of the dispersion (feed rate=20-30 mL/min). Meanwhile, kaolin clay powder (KaMin™ HG-90, Kamin LLC, Macon, Ga.) was fed (feed rate=0.5-1.5 g/min) into the dryer chamber as an anti-caking agent. The multilayer polymer particle dispersion was atomized by high air pressure at the nozzle atomizer and dried inside the chamber, and the dry powder was collected in the glass jar attached on the cyclone. The resulting redispersible polymer powder has a mean particle size of 10 to 30 μm. The test results for each redispersible polymer powder are listed in Table 3, below.

(30) The RDPs in Examples 1-17 are given in Table 3, below, along with the shelf life and redispersibility performance of each Example. The following test results were used:

(31) Shelf Life:

(32) Defined herein as the time when epoxy RDP remains >50% redispersed (as defined below) at room temperature. An acceptable shelf life is at least 1 month and, preferably, 3 months or longer.

(33) Redispersibility:

(34) The redispersibility of the RDP powders was evaluated by comparison of the particle size of the powder re-dispersed in water with the particle size of the original dispersion. The dry powder was dispersed into deionized water at 1% solid and vortexed for 30 seconds twice, and 2-3 drops of 1M NaOH solution was added to tune the pH of the redispersion to >10. The particle size of the redispersion was then measured by a Coulter LS 13 320 Laser Light Diffraction Particle Size analyzer. The redispersibility is defined as the volume percentage of particles below 1 μm in the redispersion. For instance, if the redispersion shows 20% particle below 1 μm by volume, the redispersibility of this powder is 20%.

(35) Expected Shelf Life Based on Aging Tests:

(36) To accelerate shelf life tests, the RDP examples were aged at 50° C. for different time periods as indicated in Table 3, below, and redispersibility was measured in an alkaline solution containing NaOH at a pH of 10-11. It is expected that 5 hours aging at 50° C. is roughly equivalent to 1 month at RT and that 12 hours of aging at 50° C. is roughly equivalent to 2 months at RT.

(37) TABLE-US-00005 TABLE 3 Summary Of Spray Dried Epoxy RDPs Total Multilayer Stabilizer.sup.a Polymer (wt. %, based Redispersibility (%) after RDP Particle on epoxy aging at 50° C. Shelf life Ex. Dispersion resin solids) 0 h 4 h 8 h 12 h 40 h at RT 1* E 10% PVOH 100 100 100 100 <20 5 months 2* F 10% PVOH 100 <20 — — — <1 week 3* G 11.2% PVOH 100 <20 — — — <1 week 4  G 6.2% PVOH + 100 >90 >80 >50 — 2 month 5% PVP 5* G 6.2% PVOH + 100 <20 — — — <1 weeks 5% PAM 6* G 11.2% PVOH 100 <20 — — — <1 week 7* H 11.2% PVOH 100 >80 <20 — — ~2 weeks 8  I 6.2% PVOH 100 100 100 100 80 12 months** 5% PVP 9  I 11.2% PVOH 100 100 100 100 20 6 months 10*  J 11.2% PVOH 100 ~50 <20 — — 1 month 11*  K 6.2% PVOH + 100 <20 — — — <1 week 6% PVP 12  L 6.2% PVOH + 100 50 38 — — 1 month 6% PVP 13  M 6.2% PVOH + 100 100 100 <30 — 2 months 6% PVP 14  N 6.2% PVOH + 100 100 100 100 <30 4 months** 6% PVP 15*  O 6.2% PVOH + 100 <20 — — — <1 week 6% PVP 16  P 6.2% PVOH + 100 100 100 100 15 4 Months** 6% PVP 17*  Q 6.2% PVOH + 26 <20 — — — <1 week 6% PVP *Comparative Example; **Expected shelf life based on aging tests; .sup.aTotal stabilizer includes PVOH in the seed epoxy dispersions and additional PVOH or PVP added after polymerization; PVP = polyvinylpyrrolidone (Mw = 40 kg/mol, Sigma-Aldrich, St. Louis, MO); PVOH = Mowiol ™ 488; PAM = polyacrylamide (Mn = 10 kg/mol, Sigma-Aldrich).

(38) The RDP in Comparative Example 1 in Table 3, above, remained redispersible for storage at room temperature for 5 months with a higher Tg epoxy (40° C.). However low T.sub.g epoxy RDPs in Comparative Examples 2 and 3 exhibited less than 1 week shelf stability. It is expected that lower Tg epoxy RDPs will have reduced shelf lives.

(39) In Example 9, a low Tg epoxy (Tg=15° C.) multilayer polymer particle RDP exhibited very good shelf life because a hydrophic chain transfer agent was included in the alkali soluble polymer. In contrast, in Comparative Example 10 the same polymer with a hydrophilic chain transfer agent did not give acceptable shelf life.

(40) With a low T.sub.g epoxy (Tg=15° C.) multilayer polymer particle RDP, having 6 wt. % of copolymerized methacrylic acid (30% alkali soluble polymer shell at MMA:MAA=4:1, 4% nDDM) and 6% PVP as a colloidal stabilizer, the RDP Example 12 in Table 3, above, gave a passable 1 month shelf life. However, when the copolymerized methacrylic acid level in the multilayer polymer particle drops below 5 wt. % of the alkali soluble polymer (30% alkali soluble polymer shell with 15% copolymerized acid), the RDP of Comparative Example 15 exhibited <1 week shelf life even with 6% PVP. See also Comparative Example 11. In contrast, the same polymer with 8.4 wt. % copolymerized methacrylic acid (28% acid in alkali soluble polymer present at 30 wt. % of the RDP) in Example 16 has approximately 4 months shelf life. With even more (10 wt. %) copolymerized methacrylic acid (50% alkali soluble polymer with 20% copolymerized methacrylic acid) and a PVP colloidal stabilizer in Example 14, low Tg epoxy multilayer polymer particle RDP gave 2 months shelf life even without a hydrophobic chain transfer agent.

(41) With a slightly higher Tg (22° C.) soft epoxy resin, as shown in Table 3, above, including the hydrophobic chain transfer agent even at 2 wt. % in the multilayer polymer particle RDP of the present invention greatly increases shelf life, as shown in Example 9 with 2% copolymerized nDDM and 6 months shelf life. In Example 8, including some poly(vinylpyrrolidinone) colloidal stabilizer in the same polymer RDP increased shelf life to 12 months.

(42) The effect of the colloidal stabilizer is particularly evident in Example 4 (epoxy Tg=22° C.) wherein a small amount of poly(vinylpyrrolidinone) colloidal stabilizer in the same polymer RDP increased shelf life to 2 months from less than one week with any other colloidal stabilizer in Comparative Examples 3, 5 and 6.