PROCESS OF PRODUCING POLYMER DISPERSIONS

Abstract

Disclosed herein is a process of producing a polymeric dispersion by free radical emulsion polymerization of a monomer composition including ethylenically unsaturated monomers in the presence of a block copolymer. The block copolymer has a first block including at least 80 wt.-% units of alkyl acrylate and a second block including units of an ethylenically unsaturated monomer with sulfonic acid groups. Either the first or the second block is connected with a nitroxyl radical. The polymeric dispersion is obtainable by the disclosed process, and the block copolymer is used in the process. Further disclosed herein is a method of using the block copolymer as an emulsifying agent for free radical emulsion polymerization.

Claims

1. A process of producing a polymeric dispersion, the process comprising producing the polymeric dispersion by free radical emulsion polymerization of a monomer composition comprising ethylenically unsaturated monomers in the presence of a block copolymer, wherein the block copolymer has a first block comprising at least 80 wt.-% units of alkyl acrylate and a second block comprising units of an ethylenically unsaturated monomer with sulfonic acid groups, wherein either the first or the second block is connected with a nitroxyl radical.

2. The process according to claim 1, wherein the second block has a terminal group which is a nitroxyl radical.

3. The process according to claim 1, wherein the alkyl acrylate is n-butyl acrylate.

4. The process according to claim 1, wherein the ethylenically unsaturated monomer with sulfonic acid groups is selected from the group consisting of styrene sulfonic acid, alkali salts of styrene sulfonic acid, and ammonium salts of styrene sulfonic acid.

5. The process according to claim 1, wherein the nitroxyl radical is of the formula Z ##STR00006## in which # denotes the attachment to a C atom of the polymer block, R.sup.1 and R.sup.2 independently of one another are C.sub.1-C.sub.20 alkyl, which optionally carry a substituent selected from the group consisting of C.sub.1-C.sub.4 alkoxy, C.sub.1-C.sub.4 alkoxy-C.sub.1-C.sub.4 alkoxy, and PO.sub.3R.sup.z.sub.2, and R.sup.z is C.sub.1-C.sub.4 alkyl, or are phenyl or are C.sub.7-C.sub.18 aralkyl or R.sup.1 and R.sup.2 together are linear C.sub.2-C.sub.10 alkylene or linear C.sub.2-C.sub.10 alkenylene in which optionally one or two CH.sub.2 groups may have been independently of another replaced by O, C═O, C═NOH, CH—OCOCH.sub.3 or NR.sup.x, wherein linear C.sub.2-C.sub.10 alkylene and linear C.sub.2-C.sub.10 alkenylene are unsubstituted or have 1, 2, 3, 4 or 5 substituents selected from the group consisting of C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4 alkoxy, C.sub.1-C.sub.4 alkoxy-C.sub.1-C.sub.4 alkoxy, COOH, and CONH.sub.2, and R.sup.x is C.sub.1-C.sub.4 alkyl or C.sub.1-C.sub.4 alkoxy; R.sup.3 is C.sub.1-C.sub.4 alkyl or H; R.sup.4, R.sup.5, and R.sup.6 independently of one another are C.sub.1-C.sub.4 alkyl

6. The process according to claim 1, wherein the block copolymer has ≤80 average repeating units of n-butyl acrylate.

7. The process according to claim 1, wherein the molar ratio of the monomers of the first block to the monomers of the second block is between 1:1 and 8:1.

8. The process according to claim 3, wherein 0.1 to 10 parts by weight of block copolymer based on 100 parts by weight of total monomers is used in free radical emulsion polymerization.

9. The process according to claim 1, wherein the emulsion polymerization is carried out as a feed process.

10. A block copolymer which has a first block comprising at least 80 wt.-% units of alkyl acrylate and a second block comprising units of an ethylenically unsaturated monomer with sulfonic acid groups wherein either the first or the second block has a terminal group which is a nitroxyl radical.

11. A block copolymer according to claim 10, wherein one block is connected with a nitroxyl radical of formula Z and the other block is connected with X, which is selected from the group consisting of —CH.sub.2-phenyl, —CHCH.sub.3-phenyl, —C(CH.sub.3).sub.2-phenyl, —C(C.sub.5-C.sub.6-cycloalkyl).sub.2-CN, —C(CH.sub.3).sub.2CN, —CH.sub.2CH═CH.sub.2, —CH.sub.3CH—CH═CH.sub.2, —(C.sub.1-C.sub.4alkyl)CR.sup.7—C(O)-phenyl, —(C.sub.1-C.sub.4)alkyl-CR.sup.7—C(O)—(C.sub.1-C.sub.4)alkoxy, —(C.sub.1-C.sub.4)alkyl-CR.sup.7—C(O)—(C.sub.1-C.sub.4)alkyl, —(C.sub.1-C.sub.4)alkyl-CR.sup.7—C(O)—N-di(C.sub.1-C.sub.4)alkyl, —(C.sub.1-C.sub.4)alkyl-CR.sup.7—C(O)—NH(C.sub.1-C.sub.4)alkyl, and —(C.sub.1-C.sub.4)alkyl-CR.sup.7—C(O)—N.sub.2, wherein R.sup.7 is selected from the group consisting of hydrogen and (C.sub.1-C.sub.4)alkyl.

12. A block copolymer according to claim 10, in which the monomer with sulfonic acid groups is selected from the group consisting of styrene sulfonic acid, alkali salts of styrene sulfonic acid, and ammonium salts of styrene sulfonic acid, and in which the molar ratio of the monomers of the first block to the monomers of the second block is between 1:1 and 8:1.

13. A block copolymer according to claim 10, in which the nitroxyl radical is of the formula ##STR00007##

14. A method of using the block copolymer according to claim 10, the method comprising using the block copolymer as an emulsifying agent for free radical emulsion polymerization.

15. An aqueous polymeric dispersion obtainable by the process according to claim 1.

16. The process according to claim 5, wherein R.sup.4, R.sup.5, and R.sup.6 independently of one another are methyl or ethyl.

Description

EXAMPLES

[0139] Unless the context suggests otherwise, percentages are always by weight. A reported content is based on the content in aqueous solution or dispersion if not stated otherwise.

ABBREVIATIONS

[0140] GPC: gel permeation chromatography [0141] Mn: Number average molecular weight [0142] PDI: Polydispersity (The polydispersity of a sample is defined as weight average molecular weight Mw divided by Mn and gives an indication just how narrow a distribution is.) [0143] nBA: n-butyl acrylate [0144] BcP: block copolymer [0145] NaSS: sodium styrene sulfonate [0146] HEMA: hydroxyethyl methacrylate [0147] MAA: methacrylic acid [0148] HEA: 2-hydroxyethyl acrylate [0149] MPEG350MA: Bisomer MPEG 350MA [0150] MPEG550MA: Bisomer MPEG 550MA [0151] DMF: N,N-dimethylformamide [0152] S: Styrene [0153] AA: acrylic acid

[0154] The following, quantities in pphm (parts per hundred monomer) are based on 100 weight stake of total monomer.

[0155] The abbreviated names better reflect which part of the polymer is random and which part is a block. For example the name poly(nBA-b-NaSS co HEMA) given in Example 2.11 describes a polymer comprising a block (characterized by the letter “b”) of poly sodium styrene sulfonate wherein the styrene group has at random been copolymerized with hydroxyethyl methacrylate and another block of pure poly-n-butylacrylate. The approximated numbers of the monomers in said blocks are given e.g. in Example 2.11 as 20-b-(4-co-6), i.e. there are approximately 6 hydroxyethyl methacrylate units randomly copolymerized with 4 sodium styrene sulfonate units onto a preformed block of 20 n-butyl acylate units. It should, however, be noted that the abbreviated names do not mention the end groups on both sides of the polymer, i.e. e.g. the 1-phenyl-ethyl group.

[0156] The solids contents were determined generally by drying an aliquot (about 2 g) of the aqueous polymer dispersion to constant weight at 150° C. Two separate measurements were carried out in each case. The figure reported in each of the examples represents the average of the two results.

Preparation of the Amphiphilic Block Copolymer

[0157] The production process of the amphiphilic block copolymers described below with A as initiator was carried out with 2,6-diethyl-2,3,6-trimethyl-1-(1-phenylethoxy)-4-piperidinone (hereinafter referred to as alkoxyamine A) as polymerization initiator.

Synthesis of a Linear Polybutyl Acrylate (BA)

Example 1.1: A-Block 1.1

[0158] Under nitrogen atmosphere 225 g of alkoxyamine A (0.71 mol) was dissolved in 4088 g n-butyl acrylate (31.9 mol). The mixture was degassed three times. Following which, it was heated to 115° C. and stirred at that temperature until desired monomer conversion was reached. Conversion was determined by solid content measurement according to ISO 3251. As soon as the targeted monomer conversion of n-butyl acrylate was obtained vacuum was applied and residual monomer was removed by vacuum distillation at 100° C. and 15 mbar. The solid content was >98%.

Examples 1.2 to 1.6: Preparation of A-Block 1.2 to Block 1.6

[0159] The A-Block 1.2 to 1.7 were made identical to the procedure of example 1.1 but using the respective amounts of alkoxyamine A and n-butyl acrylate given in table 1. The characteristics of the resulting A-Block copolymers 1.1 to 1.7 are given in table 2. The solid content of products was >98%.

Example 1.7: A-Block 1.7 (not According the Invention)

[0160] Under nitrogen atmosphere 25 g of alkoxyamine A was dissolved in 412 g (3.96 mol) styrene. The mixture was degassed three times. Following which, it was heated to 115° C. and stirred at that temperature until desired monomer conversion was reached. Conversion was determined by solid content measurement in analogy to ISO 3251. As soon as a monomer conversion of 40% styrene was obtained, vacuum was applied and residual monomer was removed by vacuum distillation at 110° C. and 5 mbar. The solid content was >98%. The polymer A-Block has 20 average repeating units.

TABLE-US-00001 TABLE 1 A-Block preparation Alkoxy- Conver- Average Exam- A- amine A nBA sion repeating ple Block [g]/[mol] [g]/[mol] [%] units 1.1 1.1 225/0.71 4088/31.9  44 20 1.2 1.2 166/0.52 4021/31.37 50 30 1.3 1.3 163/0.51 3296/25.72 40 20 1.4 1.4   4/0.0126 246/1.92 49 75 1.5 1.5  80/0.25 3230/25.20 50 50 1.6 1.6  80/0.25 3230/25.20 35 35 nBA = n-butyl acrylate alkoxyamine A = 2,6-diethyl-2,3,6-trimethyl-1-(1-phenylethoxy)- 4-piperidinone

Example 2.1: Synthesis of a Linear Block Copolymer poly(n-BA-b-NaSS)

[0161] Under nitrogen atmosphere 267 g sodium styrene sulfonate were dissolved in 3551 g N,N-dimethyl formamide (7% by weight NaSS) and 350 g of A-Block 1.1 was added The mixture was heated to 115° C. and stirred at that temperature until desired monomer conversion was reached. Conversion was determined by NMR measurement. As soon as full monomer conversion was obtained vacuum was applied and solvent removed by vacuum distillation at 155° C. and 5 mbar. The solid content was >99%.

Examples 2.2 to 2.10 and 2.18 to 2.25

[0162] The AB-Block polymer was made identical to the procedure of example 2.1. The A-Block polymer was added to a 7% by weight solution of NaSS in DMF. The amounts of the A-Block polymer and the NaSS are given in table 3. The solid content of the products was >99%. Characteristics of the products are summarized in table 4.

TABLE-US-00002 TABLE 2 Monomer compositions of the B-Block preparation Average Average Example A- repeating repeating No. = AB Block A-Block NaSS [g]/ units units Block No. A-Block [g] [mol] [mol] A-Block B-Block 2.1 1.1 350 0.117 267/1.29 20 10 2.2 1.3 400 0.133 305/1.48 20 10 2.3 1.2 40 0.010  33/0.16 30 15 2.4 1.2 50 0.013  28/0.14 30 10 2.5 1.2 30 0.008  33/0.16 30 20 2.6 1.4 20 0.0002  17/0.08 75 38 2.7 1.4 30 0.0003  14/0.07 75 30 2.8 1.4 22 0.0002  13/0.06 75 25 2.9 1.4 12 0.0001  12/0.06 75 45 2.10 1.1 20 0.007  12/0.06 20 8 2.18 1.5 12 0.002  16/0.06 50 38 2.19 1.5 15 0.002  13/0.06 50 25 2.20 1.6 20 0.004  14/0.07 35 15 2.21 1.5 15 0.002  10/0.05 50 20 2.22 1.5 8 0.001  13/0.06 50 45 2.23 1.5 7 0.001  14/0.07 50 60 2.24 1.6 10 0.002  18/0.09 35 30 2.25 n.i. 1.7 n.i. 16 0.007  14/0.07 20 10 n.i. not according the invention-comparative

Synthesis of a Linear Block Copolymer poly(n-BA-b-NaSS-co-HEMA) Example 2.11

[0163] Under nitrogen atmosphere 9.2 g sodium styrene sulfonate were dissolved in 122 g N,N-dimethyl formamide (7% by weight NaSS) and 8 g 2-Hydroxyethyl methacrylate followed by 30 g of A-Block 1.1 was added The mixture was heated to 115° C. and stirred at that temperature until desired monomer conversion was reached. Conversion was determined by NMR measurement. As soon as full monomer conversion was obtained vacuum was applied and solvent removed by vacuum distillation at 155° C. and 5 mbar. The solid content was >99%.

Example 2.12 to 2.17

[0164] The AB-Block polymer was made identical to the procedure of example 2.11. The A-Block polymer and the comonomer were added to a 7% by weight solution of NaSS in DMF. The amounts of the comonomer and the NaSS are given in table 3. The solid contents of the products were >99%.

TABLE-US-00003 TABLE 3 Monomer compositions of the B-Block preparation monomer [g]/[mol] Average repeating units AB-Block MPEG MPEG B- Example NaSS HEMA MAA HEA 350 MA 550 MA A-Block NaSS comonomer 2.11 9.2/0.04 8/0.06 — — — — 20 4 6 2.12 9.2/0.04 13/ — — — — 20 4 10 0.10 2.13 9.2/0.04 20/ — — — — 20 4 15 0.15 2.14 9.2/0.04 — 5/ — — — 20 4 6 0.06 2.15 9.2/0.04 — — 7/ — — 20 4 6 0.06 2.16 9.2/0.04 — — — 26/ — 20 4 6 0.06 2.17 9.2/0.04 — — — — 38/ 20 4 6 0.06

Comparative Example 2.26: Synthesis of a Linear Block Copolymer poly(n-BA-b-MAA) 20-b-11

[0165] Under nitrogen atmosphere 600 g A-Block 1.1 was dissolved in 298 g (3.46 mol) methacrylic acid, 300 g ethanol and 30 g water. The mixture was heated to 145° C. under pressure and stirred at that temperature until an average monomer conversion of 11 repeating units was reached.

[0166] Conversion was determined by NMR measurement. Afterwards, the pressure was released, vacuum applied and processing solvents as well as residual methacrylic acid were removed by vacuum distillation at 155° C. and 5 mbar. The solid content was >99%.

Analytics of the Polymer Dispersions

Determination of Particle Sizes

[0167] The distribution of particle size is determined by quasi-elastic light scattering (QELS), also known as dynamic light scattering (DLS) according to ISO 13321:1996 standard. The determination was carried out using a High-Performance Particle Sizer (Malvern) at 22° C. and a wavelength of 633 nm. For this purpose, a sample of the aqueous polymer dispersion is diluted, and the dilution will be analyzed. In the context of DLS, the aqueous dilution may have a polymer concentration in the range from 0.001 to 0.5% by weight, depending on the particle size. For most purposes, a proper concentration will be 0.01% by weight.

[0168] The reported particle size value D is the z-average (Dz) of the cumulant evaluation of the measured of the measured autocorrelation function.

Determination of pH

[0169] For pH measurement a pH electrode (SI Analytics H63) was used. The measurement was performed at room temperature with original sample.

Determination of Solids Content

[0170] The solids content was determined by drying the sample and measuring its dry weight. Therefore, a solids content device Sartorius MA 45 was used with constant weight program is used. A sample of 1.5 g prepared in a tared small aluminum pan with glass fiber pad and covered with a cap. The drying program “120° C. Automatic” is started. The glass fiber pad is pre-dried with the same program. Every sample solids content is calculated by a double determination.

Determination of Surface Tension

[0171] Surface Tension is measured by a Du-Noüy Ring tensiometer K100c from FA Krüss. For this purpose, 35 ml of the dispersion are filled undiluted into an open glass vessel. This is clamped in a double-walled container thermostatically controlled at 25° C. The platinum ring (d=19.09 mm) is locked in place on the force transducer.

[0172] The measurement is performed fully automatically: Liquid is moved up to the platinum ring from below at 100 mm/min until it is immersed 3 mm into the liquid. The liquid is then moved at 6 mm/min in the opposite direction so that the ring slowly moves towards the air/water interface. When the ring reaches the liquid/air interface, the liquid is stretched and the force as a function of the travel is recorded. Surface tension is calculated from of the maximum force. This process is repeated three times in total. The surface tensions specified in the tables are the arithmetically averaged values of three successive individual measurements. The higher the surface tension of the aqueous dispersion, the purer the aqueous phase. The theoretical maximum value of the surface tension would be the value of pure water, which is 73 mN/m at 20° C. and 1 atm.

Determination of Maximum Shear Stability

[0173] Shear tests are performed under turbulent flow conditions using a dispermat (VMA Getzmann) dissolver system. This consists of a high-speed rotor that transfers its rotational energy to a 20 mm serrated disk with 16 cogs. Undiluted dispersion is sheared for 10 minutes at 2500 rpm, 5000 rpm, 7500 rpm and 10000 rpm. The maximum shear stability is given at the speed of rotation at which the dispersion does not form coagulate, unchanged from the starting point.

[0174] The higher the value of the maximum shear stability, the more shear force can be applied until the solution coagulates.

Determination of NaCl and CaCl.SUB.2 .Stability

[0175] A small aliquot of dispersion is dropped into several salt solutions with different concentrations of 0.1%, 0.5%, 1% and 5% by weight calcium chloride and 2.5%, 5%, 10% by weight sodium chloride. The maximum salt stability is given in a salt concentration where the droplet does show still a homogeneous dilution instead of coagulation.

[0176] Salt stability: The emulsifying effect is all the better, the more stable the dispersion is even at high salt concentrations. A stability at 2.5% is therefore better than one at 1%.

Preparation of the Polymer Dispersions D1-D4

[0177] Initiator feed: 42.7 g of a 7 wt % strength aqueous solution of sodium peroxodisulphate [0178] Monomer feed: 232 g nBA (58 wt %) [0179] 168 g MMA (42 wt %) [0180] Block copolymer feed: 304.6 g of a 2.63 wt % strength aqueous solution of the block copolymer according to table 4 (2 pphm)

[0181] In a 2 L reactor with anchor stirrer, 270.40 g deionised water were filled under a nitrogen atmosphere and heated up. After reaching an internal temperature of 85° C., 12.8 g of initiator feed, 20 g monomer feed and 45.7 g block copolymer feed were added within 2 minutes and stirred for 10 minutes.

[0182] Then beginning simultaneously and with maintenance of the internal temperature of 85° C., 29.9 g initiator feed, 380 g monomer feed and 258.9 g block copolymer feed were added over 180 minutes with a constant flow rate. Thereafter the reaction mixture was stirred for another 30 minutes at 85° C. Then 7.63 g acetone bisulfite and 6 g tert-butyl hydroperoxide were added over the course of 60 minutes. The dispersion was then cooled to room temperature. This gave a polymer dispersion having a solids content of 39 wt %. The dispersion had no coagulum.

TABLE-US-00004 TABLE 4 Dispersion 1-4 (nBA/MMA ratio: 58/42 wt %/wt %) AB Surface Max Shear Max NaCl Max CaCl.sub.2 Block D tension stability stability stability Dispersion No A/B [nm] pH [mN/m] [rpm] [%] [%] D1 2.1  20/10 146 2.1 52 7500 2.5 0.1 D2 2.19 50/25 211 2.0 57 5000 2.5 0.1 D3 2.18 50/38 211 2.1 60 2500 2.5 0.1 D4 2.6  75/38 260 2.0 58 <2500 <2.5 0.1 D: Average particle size

Preparation of the Polymer Dispersions D5-D8

[0183] Initiator feed: 42.7 g of a 7 wt % strength aqueous solution of sodium peroxodisulphate [0184] Monomer feed: 232 g nBA (58 wt %) [0185] 168 g MMA (42 wt %) [0186] Water feed: 296.61 g

[0187] In a 2 L reactor with anchor stirrer, 270.04 g deionised water and 278.4 g of a 2.87 wt % aqueous solution of the block copolymer (2 pphm) according table 5 were filled under a nitrogen atmosphere and heated up. After reaching an internal temperature of 85° C., 12.8 g of initiator feed were added within 2 minutes and stirred for 5 minutes. Then beginning simultaneously and with maintenance of the internal temperature of 85° C., 29.9 initiator feed, 400 g monomer feed and water feed were added over 180 minutes with a constant flow rate. Thereafter the reaction mixture was stirred for another 30 minutes at 85° C. Then 7.63 g acetone bisulfite and 6 g tert-butyl hydroperoxide were added over the course of 60 minutes. The dispersion was then cooled to room temperature. This gave a polymer dispersion having a solids content of 39 wt %. The dispersion had no coagulum.

TABLE-US-00005 TABLE 5 Dispersion D5-D8 (nBA/MMA ratio in wt %: 58/42) AB Surface Max Shear Max NaCl Max CaCl.sub.2 Block D tension stability stability stability Dispersion No A/B [nm] pH [mN/m] [rpm] [%] [%] D5 2.1  20/10  97 1.9 52 7500 <2.5 0.1 D6 2.19 50/25 190 1.9 52 5000 <2.5 0.1 D7 2.18 50/38 199 1.8 52 <2500 <2.5 0.1 D8 2.6  75/38 237 1.9 53 <2500 <2.5 0.1 D: Average particle size

Preparation of the Polymer Dispersions D9-D12

[0188] According to the procedure described for the Dispersion D5, further dispersions D9-D12 with the block copolymer 2.1 were prepared, wherein the amount of block copolymer used was varied as follows: [0189] D9: 296.61 g of a 6.75 wt % strength aqueous solution [0190] D10: 296.61 g of a 1.35 wt % strength aqueous solution [0191] D11: 296.61 g of a 0.34 wt % strength aqueous solution [0192] D12: 296.61 g of a 0.20 wt % strength aqueous solution

TABLE-US-00006 TABLE 6 Dispersion D9-D12 Max Max Max AB Amount Surface Shear NaCl CaCl.sub.2 Block BcP D tension stability stability stability Dispersion No A/B pphm [nm] pH [mN/m] [rpm] [%] [%] D5  2.1 20/10 2 97 1.9 52 7500 <2.5 0.1 D9  2.1 20/10 5 79 1.7 51 10000 2.5 0.1 D10 2.1 20/10 1 96 1.7 51 5000 <2.5 0.1 D11 2.1 20/10 0.25 125 1.7 50 2500 <2.5 0.1 D12 2.1 20/10 0.15 143 1.7 51 <2500 <2.5 0.1 D: Average particle size

Preparation of the Polymer Dispersions D13-D14

[0193] According to the procedure described for the Dispersion D5, further dispersions D13 and D14 with the block copolymer 2.1 were prepared, wherein the monomer feed was changed by replacing 1 pphm of butyl acrylate by acrylic acid: [0194] Monomer feed: 228 g nBA (57 wt %) [0195] 168 g MMA (42 wt %) [0196] 4 g AA (1 wt %)

TABLE-US-00007 TABLE 7 Dispersion D13-D14 Max Max Max Shear NaCl CaCl.sub.2 Dis- AB Amount Surface sta- sta- sta- per- Block BcP D tension bility bility bility sion No pphm [nm] pH [mN/m] [rpm] [%] [%] D13 2.1 1 120 1.7 50 5000 <2.5 0.1 D14 2.1 1 115 8.6 46 10000 5 0.1 D: Average particle size

[0197] When preparing a dispersion including acrylic acid as comonomer the stability is further improved at neutral pH (D14).

Preparation of the Polymer Dispersions D15-D21

[0198] Initiator feed: 42.86 g of a 7 wt % strength aqueous solution of sodium peroxodisulphate [0199] Monomer feed: 232 g nBA (58 wt %) [0200] 168 g MMA (42 wt %) [0201] Block copolymer feed: 304.61 g of a 2.63 wt % strength aqueous solution of the block copolymer according to table 8 (2 pphm)

[0202] In a 2 L reactor with anchor stirrer, 15.76 g of a 33 wt. % aqueous polystyrene seed (weight-average particle diameter 30 nm), 267.64 g deionised water were filled under a nitrogen atmosphere and heated up. After reaching an internal temperature of 85° C., 8.57 g of initiator feed were added within 2 minutes and stirred for 5 minutes. Then beginning simultaneously and with maintenance of the internal temperature of 85° C., 34.29 g initiator feed, the monomer feed and the block copolymer feed were added over 180 minutes with a constant flow rate. Thereafter the reaction mixture was stirred for another 30 minutes at 85° C. Then 7.63 g acetone bisulfite and 6 g tert-butyl hydroperoxide were added over the course of 60 minutes. The dispersion was then cooled to room temperature. This gave a polymer dispersion having a solids content of 39 wt %.

Preparation of the Polymer Dispersions D22-D24

[0203] D22-D24 were prepared in analogy to D15. Only monomer feeds were changed to: [0204] Monomer feed (D22): 140 g nBA (35 wt %) [0205] 260 g MMA (65 wt %) [0206] Monomer feed (D23): 232 g nBA (58 wt %) [0207] 168 g S (42 wt %) [0208] Monomer feed (D24): 200 g EHA (50 wt %) [0209] 200 g MMA (50 wt %) [0210] Monomer feed (D25): 160 g nBA (40 wt %) [0211] 180 g MMA (45 wt %) [0212] 60 g EHA (15 wt %) [0213] Monomer feed (D26): 160 g nBA (40 wt %) [0214] 100 g MMA (25 wt %) [0215] 80 g S (20 wt %) [0216] 60 g EHA (15 wt %)

TABLE-US-00008 TABLE 8 Dispersion D15-D26 Max Max Max Shear NaCl CaCl.sub.2 Dis- AB Surface sta- sta- sta- per- Block D tension bility bility bility sion No A/B [nm] pH [mN/m] [rpm] [%] [%] D15 2.1 20/10 129 2.1 55 7500 2.5 0.1 D16 2.4 30/10 n.d. 1.8 49 7500 <2.5 0.1 D17 2.3 30/15 n.d. 1.8 51 5000 <2.5 0.1 D18 2.5 30/20 n.d. 1.5 55 2500 <2.5 0.1 D19 2.19 50/25 150 2.1 58 <2500 <2.5 0.1 D20 2.18 50/38 156 2.1 63 <2500 <2.5 0.1 D21 2.6 75/38 156 2.0 58 <2500 <2.5 0.1 D22 2.1 20/10 133 2.1 53 10000 2.5 0.1 D23 2.1 20/10 125 1.9 56 2500 2.5 0.1 D24 2.1 20/10 132 2.2 54 7500 2.5 0.1 D25 2.1 20/10 130 2.2 50 7500 2.5 0.1 D26 2.1 20/10 119 2.2 53 7500 2.5 0.1 n.d.: not determined D: Average particle size

Preparation of the Polymer Dispersion D27 (not According the Invention)

[0217] D27 was prepared in analogy to D15. Instead using 2 pphm of block copolymer, 2 pphm of an ethoxylated fatty alcohol (Disponil SDS15) was used. Additionally, the Disponil SDS15 was feeded together with the monomers instead of a separated feed: [0218] Feed: 232 g nBA (58 wt %) [0219] 168 g MMA (42 wt %) [0220] 251.28 g deionised water [0221] 53.33 g of a 15 wt % aqueous solution of Disponil SDS15 (2 pphm)

Preparation of the Polymer Dispersions D28 and D29 (not According the Invention)

[0222] D28 and D29 were prepared in analogy to D15. Instead using 2 pphm of block copolymer 2.1, 2 pphm of the block copolymer poly (S-b-NaSS) 20-b-10 (example 2.25) was used: [0223] Monomer feed (D28): 232 g nBA (58 wt %) [0224] 168 g S (42 wt %) [0225] Monomer feed (D29): 232 g nBA (58 wt %) [0226] 168 g MMA (42 wt %)

Preparation of the Polymer Dispersions D30 (not According the Invention)

[0227] D30 were prepared in analogy to D15. Instead using 2 pphm of block copolymer 2.1, 2 pphm of the block copolymer poly (n-BA-b-MAA) 20-b-11 (example 2.26) was used.

TABLE-US-00009 TABLE 9 Dispersion D27-D30 Max Max Max AB Surface Shear NaCl CaCl.sub.2 Dis- Block D tension stability stability stability persion No [nm] pH [mN/m] [rpm] [%] [%] D27 n.i. —.sup.1) 126 1.6 42 7500 2.5 0.1 D28 n.i. 2.25 144 2 55 <2500 <2.5 <0.1 S/NaSS D29 n.i 2.25 131 2 50 2500 <2.5 0.1 S/NaSS D30 n.i. 2.26 —* —* —* —* —* —* n.i. not according the invention - comparative D: Average particle size .sup.1)ethoxylated fatty alcohol (Disponil SDS15) was used instead of the block copolymer *Determination not possible, dispersion coagulated while synthesis

[0228] D27 (not according the invention) has a comparatively low surface tension since. This dispersion will show disadvantages in water sensitivity and leaching compared to dispersions D1 to D24 with comparatively high surface tension.

[0229] In order to be able to compare the influence of different block copolymers, it is necessary to compare examples with the same monomer compositions. The examples D23 and D15 are suitable as a comparison to the non-inventive examples D28 and D29. Although D28 and D29 show a sufficient surface tension, they do not exhibit enough colloidal stability in terms of shear load and electrolytes, as dispersion D15 and D23 do.

[0230] Since dispersion D30 (not according the invention) coagulated already during the start of the free radical emulsion polymerization, it was not possible to determine the surface tension, shear stability and salt stability. Example D30 proves that polymerization in the presence of carboxyl group-containing block copolymers is not possible when this is carried out in the acidic pH range. In order to limit the comparability of the dispersions to the block copolymer only, polymerization is carried out in the acidic medium.