METHOD FOR PREPARING AN AQUEOUS POLYMER DISPERSION FROM A VINYL AROMATIC COMPOUND AND A CONJUGATED ALIPHATIC DIENE

Abstract

The present invention relates to a process for producing an aqueous polymer dispersion by free-radically initiated aqueous emulsion polymerization, by polymerizing, in an aqueous medium,

(a) 40 to 75 parts by weight of at least one vinylaromatic compound and
(b) 24.9 to 59.9 parts by weight of at least one conjugated aliphatic diene
(c) 0.1 to 10 parts by weight of at least one monomer comprising acid groups and
(d) 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer,
the amounts of the monomers (a) to (d) adding up to 100 parts by weight,
in a monomer feed process in the presence of at least one inorganic peroxide and at least one organic peroxide, with the proviso that the continuous metering of the inorganic peroxide starts at the same time as the continuous metering of the vinylaromatic compound, the metering of the organic peroxide is started at a time at which at least 5% and not more than 20% of the vinylaromatic compound has already been metered in in a continuous mass flow under polymerization conditions and optionally a portion of the inorganic peroxide is initially charged,
and also to the aqueous polymer dispersions produced by the process and to the use of these as a binder, adhesive, sizing agent for fibers, for the production of coatings or for the production of a paper coating slip.

Claims

1. A process for producing an aqueous polymer dispersion by free-radically initiated aqueous emulsion polymerization, which comprises polymerizing, in an aqueous medium, (a) 40 to 75 parts by weight of at least one vinylaromatic compound and (b) 24.9 to 59.9 parts by weight of at least one conjugated aliphatic diene (c) 0.1 to 10 parts by weight of at least one monomer comprising acid groups and (d) 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer, the amounts of the monomers (a) to (d) adding up to 100 parts by weight, in a monomer feed process in the presence of at least one inorganic peroxide and at least one organic peroxide, with the proviso that the continuous metering of the inorganic peroxide starts at the same time as the continuous metering of the vinylaromatic compound, the metering of the organic peroxide is started at a time at which at least 5% and not more than 20% of the vinylaromatic compound has already been metered in in a continuous mass flow under polymerization conditions and optionally a portion of inorganic peroxide is initially charged.

2. The process according to claim 1, wherein the vinylaromatic compound is styrene and/or methylstyrene and the conjugated aliphatic diene is 1,3-butadiene and/or isoprene.

3. The process according to claim 1, wherein during the monomer feed no reducing agent capable of forming a redox initiator system with the organic or inorganic peroxides is present.

4. The process according to claim 1, wherein the inorganic peroxide is selected from hydrogen peroxide and ammonium or alkali metal salts of peroxodisulfates and the organic peroxide is selected from alkyl hydroperoxides and aryl hydroperoxides.

5. The process according to claim 1, wherein the polymerization is initiated in an aqueous polymerization mixture comprising up to 5% of the vinylaromatic compound and no aliphatic diene.

6. The process according to claim 1, wherein polymerization is effected at a temperature in the range from ≥80° C. to ≤105° C.

7. The process according to claim 1, wherein 15 to 60 parts by weight of a degraded starch are used per 100 parts by weight of the monomers.

8. The process according to claim 1, wherein the polymerization is conducted in the presence of an aqueous dispersion of finely divided polystyrene having an average particle diameter of 20 to 40 nm.

9. The process according to claim 1, wherein no chain transfer agent selected from aliphatic and/or araliphatic halogen compounds, organic thio compounds and substituted thiols is used during the polymerization.

10. An aqueous polymer dispersion obtainable by free-radically initiated emulsion polymerization according to claim 1.

11. A method comprising utilizing the aqueous polymer dispersion according to claim 10 as a binder, adhesive, sizing agent for fibers, for the production of coatings or for the production of paper coating slips.

12. A paper coating slip comprising (i) inorganic pigments and (ii) an aqueous polymer dispersion according to claim 10 and optionally further auxiliaries.

13. The paper coating slip according to claim 12, wherein the polymers of the aqueous polymer dispersion are used in an amount of 1 to 50 parts by weight based on the total amount of pigments, and wherein the pigments are present in an amount of 80 to 95 parts by weight based on the total solids content and are selected from the group consisting of calcium sulfate, calcium aluminate sulfate, barium sulfate, magnesium carbonate, calcium carbonate, silicas, aluminum oxides, aluminum hydroxide, silicates, titanium dioxide, zinc oxide, kaolin, alumina, talc and silicon dioxide, and wherein the paper coating slip additionally comprises at least one auxiliary selected from the group consisting of thickeners, further polymeric binders, co-binders, optical brighteners, fillers, leveling agents, dispersants, surfactants, lubricants, neutralizing agents, defoamers, deaerators, preservatives and dyes.

14. A paper or board coated with a paper coating slip according to claim 12.

15. A process for coating paper or board, wherein an aqueous polymer dispersion according to claim 10 is provided; and a paper coating slip is produced using the aqueous polymer dispersion, at least one pigment and optional further auxiliaries; and the paper coating slip is applied to at least one surface of paper or board.

Description

EXAMPLES

[0119] Unless the context indicates otherwise, percentages always signify weight percent. Contents reported relate to the content in an aqueous solution or dispersion. The indication pphm (parts per hundred monomers) denotes the proportion by weight based on 100 parts by weight of monomer.

[0120] Where water was used in the context of the examples, demineralized water was used.

[0121] Glass Transition Temperature T.sub.G

[0122] The glass transition temperature is determined in accordance with DIN 53765 using a TA8000 series DSC820 instrument from Mettler-Toledo Int. Inc.

[0123] Determination of gel content A polymer film is produced from the dispersion by drying in a silicone mold. Rectangles of approx. 2×1.5 cm side length are punched out from this and weighed. The pieces are then placed in a petri dish with methyl ethyl ketone and left there at room temperature for 48 hours. The un-crosslinked portion of the polymer dissolves in the solvent in the course of this. After this time has elapsed, the polymer pieces are removed from the solvent, dried for one hour at 140° C. and reweighed. The weight loss corresponds to the soluble portion of the polymer and the insoluble portion is the so-called gel. This insoluble weight fraction based on the weight of the dried total polymer is the so-called gel content.

[0124] Determination of the 4-PCH Content

[0125] The 4-phenylcyclohexene content is determined by means of gas chromatography (direct injection). It is reported in ppm based on the dispersion.

[0126] Determination of the Coagulate

[0127] The amount of coagulate in the dispersion is based on particles having a diameter of >45 μm. It was determined by filtering the finished dispersion through a sieve with a known pore diameter.

[0128] The following feedstocks were used in the examples: [0129] Emulsifier A: sodium lauryl sulfate in the form of a 15% by weight solution (Disponil® SDS from BASF) [0130] Emulsifier B: ethoxylated sodium lauryl ether sulfate in the form of a 28% by weight solution (Texapon® NSO P from BASF) [0131] Complexing agents: EDTA in the form of a 2% by weight solution (Triton® BX from BASF) [0132] Seed latex: Polystyrene seed in the form of a 29.7% by weight dispersion with a particle size of approx. 30 nm (determined by means of analytical ultracentrifugation) [0133] Initiator A: 7% by weight solution of sodium peroxodisulfate (NaPS) [0134] Initiator B: 10% by weight solution of tert-butyl hydroperoxide [0135] Reducing agent: 13% by weight solution of acetone bisulfite [0136] Degraded starch: commercial 72% by weight aqueous glucose syrup with a DE value (dextrose equivalent) of 28

[0137] In all examples, the metering of the feeds was effected in a uniform mass flow.

[0138] Production of the Emulsion Polymers

[0139] The following quantities in pphm (parts per hundred monomer) are based on 100 parts by weight of total monomer.

Example 1 Emulsion Polymerization of Styrene/Butadiene/Acrylic Acid

[0140]

TABLE-US-00001 Initial charge: 47.48 g of styrene (2.11 pphm) 192.86 g of a 7% by weight aqueous solution of itaconic acid (0.6 pphm) 4.5 g of acrylic acid (0.2 pphm) 75.76 g of a 29.7% by weight dispersion of a polystyrene latex with an average particle size of 30 nm (1.0 pphm) 18 g of a 15% by weight solution of sodium lauryl sulfate (emulsifier A) (0.12 pphm) 11.25 g of a 2% by weight solution of EDTA (complexing agent) (0.01 pphm) 86.79 g of a 7% by weight solution of sodium peroxodisulfate (initiator A) (0.27 pphm) Feed 1: 1252.13 g of styrene (55.6 pphm) Feed 2: 90 g of acrylic acid (4.0 pphm) 36 g of a 15% by weight solution of sodium lauryl sulfate (0.24 pphm) 40.18 g of a 28% by weight solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.5 pphm) 37.5 g of 15% by weight sodium hydroxide solution (0.25 pphm) 598 ml of water Feed 3: 842.4 g of butadiene (37.44 pphm) Feed 4: 273.21 g of a 7% by weight solution of sodium peroxodisulfate (initiator A) (0.85 pphm) Feed 5: 231.7 g of a 10% by weight solution of tert-butyl hydroperoxide (initiator B) (1.03 pphm) Feed 6: 66.98 g of acetone bisulfite (0.39 pphm)

[0141] The components of the initial charge and 360 ml of water were placed in a 6 l pressure reactor. The components of the initial charge were mixed and heated to 90° C. The polymerization was then started by adding 0.27 pphm of initiator A.

[0142] Immediately afterwards, feeds 1, 2 and 4 were begun (time: 0 minutes), feeds 1 and 2 being effected over the course of 4 hours and feed 4 being effected over a period of 4 hours and 15 minutes. The butadiene feed (feed 3) started 30 minutes after the start (time: 30 minutes) of feeds 1, 2 and 4 and was effected over the course of 3.5 hours. Feed 5 started at the same time as the butadiene (time: 30 minutes). For this feed, an amount of 0.8 pphm was metered in over 3 hours. The addition was then interrupted and resumed after 75 minutes. This second metering stage was effected over a period of 2 hours, in parallel with the addition of feed 6. Immediately before the addition of feed 5 was resumed, 15 g of a 15% by weight sodium hydroxide solution (0.1 pphm) were added. Finally, the mixture was cooled down to room temperature and neutralized to a pH of 6-7 with sodium hydroxide solution.

[0143] The metering of the various feeds in example 1 can be shown in the following overview:

TABLE-US-00002 Time [min] Feed 1 Feed 2 Feed 3 Feed 4 Feed 5 Feed 6 0 Initial charge 90° C. + initiator A + monomers of the initial charge 0 started started started 30 started started 210 stopped (0.8 pphm) 240 stopped stopped stopped 255 stopped 285 Addition of sodium started started hydroxide solution 405 stopped stopped

Example 2 (without Delayed Addition of the Butadiene)

[0144] Example 2 was conducted in analogy to example 1, with the difference that feeds 1 to 4 are started at the same time (all at time 0). Feed 3 ends at the time: 240 min

Examples 3 and 4

[0145] Examples 3 and 4 were conducted in analogy to example 1, the addition of the butadiene being started 60 minutes (example 3) or 90 minutes (example 4) after the start of feeds 1, 2 and 4. Feeds 1 to 3 were ended after 240 min.

Example 5

[0146] Example 5 was conducted in analogy to example 1, with the difference that the amount of styrene was increased by 2 pphm (57.6 pphm of styrene) and the amount of butadiene was reduced by 2 pphm (35.44 pphm of butadiene).

Example 6 (without Delayed Addition of Butadiene)

[0147] The emulsion polymerization was conducted as in example 1, with the difference that the metered addition of feed 3 started at the same time as feeds 1, 2 and 4 and ended after 240 minutes. A further difference was that 53.6 pphm of styrene were metered in (reduced by 2 pphm) and the amount of butadiene was increased by 2 pphm (39.44 pphm of butadiene).

Example 7

[0148] Example 7 was conducted in analogy to example 1, with styrene being increased by 8 pphm (53.6 pphm of styrene) and the amount of butadiene being reduced by 8 pphm (29.44 pphm of butadiene).

Example 8

[0149] (Without Delayed Addition of the Butadiene)

[0150] The emulsion polymerization was conducted as in example 1, with the difference that the metered addition of feed 3 started at the same time as feeds 1, 2 and 4 and ended at the same time as feeds 1 and 2 (after 240 min). A further difference was that the amount of styrene was increased by 8 pphm and the amount of butadiene was reduced by 8 pphm.

Example 9

[0151] The emulsion polymerization was conducted as in example 1, with the difference that the amount of styrene was increased by 10 pphm and the amount of butadiene was reduced by 10 pphm.

TABLE-US-00003 TABLE 1 Overview of the reaction conditions of the various examples and the properties of the polymer dispersions Butadiene delay Butadiene Styrene T.sub.G Gel content PCH content Ex. [min] [pphm] [pphm] [° C.] [%] [ppm] 1 30 37.44 55.6 4 91 10 2 0 37.44 55.6 9 90 40 3 60 37.44 55.6 −4 90 20 4 90 37.44 55.6 −9 92 15 5 30 35.44 57.6 10 88 15 6 0 39.44 53.6 3 93 35 7 30 29.44 63.6 21 88 10 8 0 29.44 63.6 26 87 35 9 30 27.44 65.6 26 84 15

[0152] All of the dispersions obtained from examples 1-9 had low amounts of coagulate.

Example 10

[0153]

TABLE-US-00004 Initial charge: .sup.  93.96 g of a 29.7% by weight dispersion of a polystyrene latex with an average particle size of 30 nm (1.6 pphm)  6.25 g of a 28% by weight solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.1 pphm)  8.75 g of a 2% by weight solution of EDTA (complexing agent) (0.01 pphm) 743.75 g  of a 72% by weight aqueous glucose syrup (DE value 28) (30 pphm)   25 g of a 7% by weight solution of sodium peroxodisulfate (initiator A) (0.1 pphm) Feed 1: 997.5 g of styrene (57 pphm)  52.5 g of acrylic acid (3 pphm) Feed 2: .sup. 250 g of a 7% by weight aqueous solution of itaconic acid (1.0 pphm) Feed 3: 682.5 g of butadiene (39 pphm) Feed 4: .sup. 175 g of a 7% by weight solution of sodium peroxodisulfate (initiator A) (0.7 pphm) Feed 5: 192.5 g of a 10% by weight solution of tert-butyl hydroperoxide (initiator B) (1.1 pphm) Feed 6: 45.42 g of acetone bisulfite (0.34 pphm)

[0154] The initial charge was placed in 442.08 g of water in a 6 l pressure reactor. The initial charge was heated to 90° C. in a reactor. 0.1 pphm of initiator A was then added.

[0155] Feeds 1, 2, 4 and 5 were then started at the same time, feed 2 being added over a period of 30 min and feeds 1 and 4 being added over a period of 2.5 hours. The butadiene feed (feed 3) started 30 minutes after the start of feeds 1, 2, 4 and 5 and was effected over the course of 2 hours (end point after 150 minutes). Feed 5 was stopped after 2.5 hours after the addition of 0.9 pphm. After 3 hours and 30 min, 70 g of a 15% by weight sodium hydroxide solution (0.6 pphm) were metered in and then the remaining amount of feed 5 was metered in in parallel with feed 6 over the course of 2 hours. Finally, the mixture was cooled down to room temperature and neutralized to a pH of 6-7 with sodium hydroxide solution.

Example 11 (without Delayed Addition of the Diene)

[0156] The emulsion polymerization was conducted as in example 10, with the difference that feeds 1, 2, 3, 4 and 5 are started at the same time (all at time 0) and are ended at the same time (time 150 min).

Example 12 (According to the Invention)

[0157] Example 12 was conducted in analogy to example 10, the addition of the butadiene being started 15 minutes after the start of feeds 1, 2, 4 and 5 and being ended jointly with these.

TABLE-US-00005 TABLE 2 Overview of the reaction conditions of examples 10-12 and the properties of the polymer dispersions Butadiene delay Butadiene Styrene T.sub.G Gel content PCH content Ex. [min] [pphm] [pphm] [° C.] [%] [ppm] 10 30 39 57 −3 95 <10 11 0 39 57 6 95 25 12 15 39 57 4 95 <10 T.sub.G glass transition temperature

[0158] All of the dispersions obtained according to examples 1-12 had low amounts of coagulate. The particle sizes of the polymer particles resulted from the seed control and did not display any significant deviations as a result of the delays in the diene feed.

[0159] The advantages of a mode of operation with delay in the diene feed are clearly apparent from tables 1 and 2. The amount of the odor-causing agent 4-PCH is in each case markedly lower than in the examples 2, 6, 8 and 11 not according to the invention. At the same time, a smaller amount of the diene can be used to achieve a desired glass transition temperature (see experiments 1 and 6, 2 and 5, and 8 and 9). When using the process according to the invention, a use amount of butadiene which is reduced by 2 pphm suffices for the production of a polymer with virtually identical glass transition temperature T.sub.G.

[0160] For the same proportion of diene, the gel content of the dispersions is not significantly modified as a result of the delayed feed.

Example 13 (Organic Peroxide in Initial Charge; Analogous to WO 2005/016977—not According to the Invention)

[0161]

TABLE-US-00006 Initial charge: 500.00 g of water (27.18 pphm) 132.14 g of a 7% by weight aqueous solution of itaconic acid (0.5 pphm) 112.00 g of a 29.7% by weight dispersion of a polystyrene latex with an average particle size of 30 nm (2.01 pphm) 4.00 g of a 28% by weight solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.06 pphm) 2.50 g of a 2% by weight solution of EDTA (complexing agent) (0.009 pphm) Addition 1: 14.44 g of a 95% by weight solution of tert-butyl peroxybenzoate (initiator A) (0.75 pphm) 50.00 g of water (2.72 pphm) Feed 1: 1000.00 g of styrene (54.37 pphm) Feed 2: 80 g of acrylic acid (4.35 pphm) 30 g of a 28% by weight solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.46 pphm) 20.0 g of 25% by weight sodium hydroxide solution (0.27 pphm) 476.9 ml of water (25.93 pphm) Feed 3: 750 g of butadiene (40.78 pphm) Feed 4: 480 g of a 7% by weight solution of sodium peroxodisulfate (initiator B) (1.83 pphm) Feed 5: 42.3 g of a 10% by weight solution of tert-butyl hydroperoxide (initiator C) (0.23 pphm) Feed 6: 54.76 g of a 13.1% by weight solution of acetone bisulfite (0.39 pphm)

[0162] The components of the initial charge were placed in a 6 l pressure reactor and mixed. 5% of the entire feed 1 and 5% of the entire feed 2 were then added. The initial charge was heated to 95° C. Initiator A (addition 1) was added slowly at 95° C.

[0163] Immediately afterwards, feeds 1, 2, 3 and 4 were begun. Feeds 1, 2 and 3 were effected over the course of 4 hours. Feed 4 was effected over a period of 4 hours and 30 minutes. After the end of feed 4, the polymerization mixture was stirred further for an additional 30 minutes. Feeds 5 and 6 were then started and effected over the course of 1 hour. After the end of feeds 5 and 6, the polymerization mixture was cooled to room temperature.

Example 14 (not According to the Invention)

[0164]

TABLE-US-00007 Initial charge: 500.00 g of water (27.18 pphm) 132.14 g of a 7% by weight aqueous solution of itaconic acid (0.5 pphm) 112.00 g of a 29.7% by weight dispersion of a polystyrene latex with an average particle size of 30 nm (2.01 pphm) 4.00 g of a 28% by weight solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.06 pphm) 2.50 g of a 2% by weight solution of EDTA (complexing agent) (0.009 pphm) Addition 1: 65.00 g of a 10% by weight solution of tert-butyl hydroperoxide (initiator C) (0.35 pphm) Feed 1: 1000.00 g of styrene (54.37 pphm) Feed 2: 80 g of acrylic acid (4.35 pphm) 30 g of a 28% by weight solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.46 pphm) 20.0 g of 25% by weight sodium hydroxide solution (0.27 pphm) 462.46 ml of water (25.14 pphm) Feed 3: 750 g of butadiene (40.78 pphm) Feed 4: 480 g of a 7% by weight solution of sodium peroxodisulfate (initiator B) (1.83 pphm) Feed 5: 42.3 g of a 10% by weight solution of tert-butyl hydroperoxide (initiator C) (0.23 pphm) Feed 6: 54.76 g of a 13.1% by weight solution of acetone bisulfite (0.39 pphm)

[0165] The components of the initial charge were placed in a 6 l pressure reactor and mixed. 5% of the entire feed 1 and 5% of the entire feed 2 were then added. The initial charge was heated to 95° C. Initiator C (addition 1) was added slowly at 95° C.

[0166] Immediately afterwards, feeds 1, 2, 3 and 4 were begun. Feeds 1, 2 and 3 were effected over the course of 4 hours. Feed 4 was effected over a period of 4 hours and 30 minutes. After the end of feed 4, the polymerization mixture was stirred further for an additional 30 minutes. Feeds 5 and 6 were then started and effected over the course of 1 hour. After the end of feeds 5 and 6, the polymerization mixture was cooled to room temperature.

Example 15 (According to the Invention)

[0167]

TABLE-US-00008 Initial charge: 500.00 g of water (27.18 pphm) 132.14 g of a 7% by weight aqueous solution of itaconic acid (0.5 pphm) 112.00 g of a 29.7% by weight dispersion of a polystyrene latex with an average particle size of 30 nm (2.01 pphm) 4.00 g of a 28% by weight solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.06 pphm) 2.50 g of a 2% by weight solution of EDTA (complexing agent) (0.009 pphm) Addition 1: 52.55 g of a 7% by weight solution of sodium peroxodisulfate (initiator B) (0.20 pphm) Feed 1: 1000.00 g of styrene (54.37 pphm) Feed 2: 80 g of acrylic acid (4.35 pphm) 30 g of a 28% by weight solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.46 pphm) 20.0 g of 25% by weight sodium hydroxide solution (0.27 pphm) 650.46 ml of water (35.37 pphm) Feed 3: 750 g of butadiene (40.78 pphm) Feed 4: 210.20 g of a 7% by weight solution of sodium peroxodisulfate (initiator B) (0.8 pphm) Feed 5: 65.00 g of a 10% by weight solution of tert-butyl hydroperoxide (initiator C) (0.35 pphm) Feed 6: 42.3 g of a 10% by weight solution of tert-butyl hydroperoxide (initiator C) (0.23 pphm) Feed 7: 54.76 g of a 13.1% by weight solution of acetone bisulfite (0.39 pphm)

[0168] The components of the initial charge were placed in a 6 l pressure reactor and mixed. 5% of the entire feed 1 and 5% of the entire feed 2 were then added. The initial charge was heated to 95° C. Initiator B (addition 1) was added slowly at 95° C.

[0169] Immediately afterwards, feeds 1, 2, 3 and 4 were begun. Feeds 1, 2 and 3 were effected over the course of 4 hours. Feed 4 was effected over a period of 4 hours and 30 minutes. Feed 5 started 30 minutes after the start of feeds 1, 2, 3 and 4 and was effected over the course of 3 hours. After the end of feed 4, the polymerization mixture was stirred further for an additional 30 minutes. Feeds 6 and 7 were then started and effected over the course of 1 hour. After the end of feeds 6 and 7, the polymerization mixture was cooled to room temperature.

Example 16 (not According to the Invention)

[0170]

TABLE-US-00009 Initial charge: 500.00 g of water (27.18 pphm) 132.14 g of a 7% by weight aqueous solution of itaconic acid (0.5 pphm) 112.00 g of a 29.7% by weight dispersion of a polystyrene latex with an average particle size of 30 nm (2.01 pphm) 4.00 g of a 28% by weight solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.06 pphm) 2.50 g of a 2% by weight solution of EDTA (complexing agent) (0.009 pphm) Addition 1: 52.55 g of a 7% by weight solution of sodium peroxodisulfate (initiator B) (0.20 pphm) Feed 1: 1000.00 g of styrene (54.37 pphm) Feed 2: 80 g of acrylic acid (4.35 pphm) 30 g of a 28% by weight solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.46 pphm) 20.0 g of 25% by weight sodium hydroxide solution (0.27 pphm) 650.46 ml of water (35.37 pphm) Feed 3: 750 g of butadiene (40.78 pphm) Feed 4: 210.20 g of a 7% by weight solution of sodium peroxodisulfate (initiator B) (0.8 pphm) Feed 5: 65.00 g of a 10% by weight solution of tert-butyl hydroperoxide (initiator C) (0.35 pphm) Feed 6: 42.3 g of a 10% by weight solution of tert-butyl hydroperoxide (initiator C) (0.23 pphm) Feed 7: 54.76 g of a 13.1% by weight solution of acetone bisulfite (0.39 pphm)

[0171] The components of the initial charge were placed in a 6 l pressure reactor and mixed. 5% of the entire feed 1 and 5% of the entire feed 2 were then added. The initial charge was heated to 95° C. Initiator B (addition 1) was added slowly at 95° C.

[0172] Immediately afterwards, feeds 1, 2, 3, 4 and 5 were begun. Feeds 1, 2 and 3 were effected over the course of 4 hours. Feed 4 was effected over a period of 4 hours and 30 minutes. Feed 5 was effected over the course of 3 hours. After the end of feed 4, the polymerization mixture was stirred further for an additional 30 minutes. Feeds 6 and 7 were then started and effected over the course of 1 hour. After the end of feeds 6 and 7, the polymerization mixture was cooled to room temperature.

TABLE-US-00010 TABLE 3 Various metering times of the initiators Chemical Initial deodorization Example charge Polymerization Redox initiator 13 n.i. tert-butyl sodium peroxodisulfate tert-butyl peroxyben- hydroperoxide + zoate acetone bisulfite 14 n.i. tert-butyl sodium peroxodisulfate tert-butyl hydroper- from the start hydroperoxide + oxide acetone bisulfite 15 sodium sodium peroxodisulfate tert-butyl peroxodi- from the start hydroperoxide + sulfate tert-butyl hydroperoxide acetone bisulfite after 30 min of monomer feed 16 n.i. sodium sodium peroxodisulfate + tert-butyl peroxodi- tert-butyl hydroperoxide + sulfate hydroperoxide acetone bisulfite both from the start n.i.: not according to the invention