DD231363A5 - METHOD FOR POLYMERIZING VINYL CHLORIDE - Google Patents

Abstract

The invention relates to a process for the suspension polymerization of vinyl chloride, optionally in the presence of monomers suitable for copolymerization or polymers suitable for graft polymerization, wherein at least one water-soluble, organic, hydroxylated carboxylic acid or its water-soluble salt and at least one other water-soluble reducing agent are used as polymerization auxiliaries and Polymerization is carried out in an apparatus whose surfaces, which come into contact with the polymerization mixture, are coated with a compound which is derived from phenoxazine or phenthiazine. By means of the combination of measures according to the invention, a particularly coating-free polymerization is achieved, which makes it possible to carry out more than 30 sets in succession without forming a visible coating on the surfaces of the apparatus.

Description

Process for the polymerization of vinyl chloride Field of application of the invention

The invention relates to a method according to claim 1.

Characteristic of the known technical solutions

During the polymerization of vinyl chloride in aqueous suspension, deposits and encrustations form on the surfaces of the apparatus which come into contact with the polymerization mixture, which interfere with the course of the polymerization and as a rule must be removed mechanically. Numerous methods by older and newer patent applications are known for reducing or avoiding crust formation, which show that on the one hand the avoidance of deposit formation is an important task, but on the other hand apparently could not yet be solved satisfactorily.

It is known from DE-OS 22 48 607 to polymerize vinyl chloride in the presence of water-soluble reducing agents at a minimum flow rate and low surface roughness of the inner surfaces of the apparatus. According to DE-OS 27 39 708 is polymerized in the presence of anions derived from organic, hydroxylated carboxylic acids. In DE-OS 29 19 197 and DE-OS 29 19 258, the use of compounds derived from Phenoxazines or Phenthiazinen and containing at least one quinoid cyclohexadiene ring, for coating the apparatus parts that come into contact with the polymerization, described. The application of the individual known methods leads, as shown in the following comparative experiments B ₉ C and E, to a more or less effective coating prevention, which makes it possible in the most favorable case to drive up to 4 comparable polymerization approaches in a row without formation of wall covering.

A combination of the teaching of 2 of the known methods leads, as shown in the following comparative experiments D, F and G, to an improvement which makes it possible, in the most favorable case, to carry out up to 7 comparable polymerization batches in succession without deposit formation.

Reaction products of the phenoxazine or phenthiazine derivatives with silanes for the internal coating of polymerization apparatus are known from DE-OS 31 49 320. By this method can also be an improvement

tion compared to the known from DE-OS 29 19 197 and DE-OS 29 19 258 methods are achieved, which consists in that the walls of the polymerization kettle does not have to be treated again after each approach, but also here after a few successive driven approaches deposit formation detected. In addition, the wall coating requires more effort than the earlier methods.

Purpose of the invention

The present invention solves the problem, considerably more polymerization approaches than by the known methods possible in a row in a polymerization without sediment formation and intermediate cleaning to drive without having to make a comparatively expensive wall coating.

Explanation of the essence of the invention

It has now been found that a wall coating of the polymerization apparatus according to DE-OS 29 19 197 or DE-OS 29 19 258 combined with a polymerization in the presence of a water-soluble, organic, hydroxylated carboxylic acid or its water-soluble salt and another water-soluble reducing agent, the deposit formation at the suspension polymerization of vinyl chloride substantially more suppressed than it is at. Application of the individual measures on their own or in any combination of two of these measures.

The effect of the combination according to the invention goes far beyond what would have been expected to be purely additive from the individual measures, so that a synergistic effect must be assumed. The novel process for the polymerization of vinyl chloride in aqueous suspension in the presence of at least one oil-soluble, radically decomposed

the catalyst, at least one suspension stabilizer and further polymerization auxiliaries and optionally in the presence of up to 50 wt .-%, based on vinyl chloride, at least one monomer which is copolymerizable with vinyl chloride and / or a polymer which is graft polymerizable with vinyl chloride, characterized in that the polymerization auxiliaries used are:

a) at least one water-soluble, organic, hydroxylated carboxylic acid or its water-soluble salt and

b) at least one further water-soluble reducing agent not mentioned under a),

wherein the polymerization is carried out in an apparatus whose surfaces are covered with the polymerization mixture

are coated with at least one compound derived from the phenoxazine or phenthiazine, at least one quinoid cyclohexadiene ring substituted in the 1,4-position with 2 N atoms, and containing at least one benzene ring, wherein the latter is substituted with at least one -OH group or -NH group.

At least two water-soluble polymerization auxiliaries, listed above under a) and b), are used. "Water-soluble" means that at least 1 g of the respective substance dissolves in 1 dm ^{3 of} water at 20 ° C.

The organic hydroxylated carboxylic acid can be derived from an aliphatic, an aromatic or a mixed aliphatic-aromatic hydrocarbon. It contains at least 2 C-atoms, at least 1 OH-group and apart from this OH-group at least one COOH-group. Preference is given to using those carboxylic acids which contain 2 to 8 C atoms, 1 to 5 OH groups and, in addition to these OH groups, 1 to 3 COOH groups. Hydroxylated carboxylic acids having a higher C atom number above 8, if they contain only 1 OH group and 1 COOH group, are generally no longer sufficiently soluble in water as the free acid; their salts, for example the sodium or potassium salts, have sufficient solubility, however, there is a danger that the free acids will fill up if the polymerization is carried out at a pH below 7. In the case of several OH grafts and / or COOH groups in the molecule, hydroxylated carboxylic acids having a C atom number above 8 are also sufficiently water-soluble, but such compounds are generally not readily available. Examples of suitable hydroxylated carboxylic acids are glycolic acid, lactic acid, malic acid, tartaric acid, citric acid, salicylic acid. Tartronic acid, ascorbic acid,

Gluconic acid, dihydroxybenzoic acids, 2,5-dihydroxyphenylacetic acid. The hydroxylated carboxylic acids may be used in the form of their water-soluble salts, for example, the sodium, potassium or ammonium salts, but it is generally preferable to use the free acids to keep the pH of the reaction mixture below 7. It is also possible to use mixtures of a plurality of hydroxylated carboxylic acids or carboxylic acid salts.

From the hydroxylated carboxylic acids 0.01 to 1 wt .-%, in particular 0.05 to 0.50 wt .-%, based on the monomers used, are advantageously used. Below 0.01% by weight, the desired effect is greatly diminished, above 1% by weight, no additional effect is generally found which would justify a higher addition level.

As b) called water-soluble reducing agent is advantageously used in vinyl chloride as little as possible soluble compound. Further, a reducing agent is suitably used which does not deteriorate the thermostability and / or other properties of the produced polyvinyl chloride.

The water-soluble reducing agent should be present in not too large amounts in the polymerization mixture, since otherwise it delays the polymerization deutlieh. 0.0005 to 0.1% by weight, in particular 0.001 to 0.03% by weight, based on the monomers used, are advantageously used. Below 0.0005% by weight, a sufficient effect is often no longer found. Suitable reducing agents, for example, are stannous or titanium III compounds, such as SnCl ₂ ; TiCl ₃ . Advantageously, those reducing agents are used which form an anion in aqueous solution containing an oxygen compound of sulfur, nitrogen or phosphorus, such as sulfoxylates, dithionites, sulfites, disulfites, dithionates, thiosulfates, nitrites, hypophosphites, hypodiphosphites, phosphites, diphosphites, hypodiphosphates. -

For coating the surfaces of the apparatus which come into contact with the polymerization mixture, compounds of the following formula ## STR3 ## which are derived from phenoxazine are suitable:

X,

in which the individual substituents mean the following:

R, R "= H; saturated hydrocarbon radical having 1 to 8 C atoms, preferably aliphatic hydrocarbon radical having 1 to 6 C atoms;

R ₃ , R ₄ ,

R "R, = H; saturated hydrocarbon radical having 1 to 8 C atoms, preferably aliphatic hydrocarbon radical having 1 to 6 C atoms; OH; O-saturated hydrocarbon radical having 1 to 8 C atoms, preferably O-aliphatic hydrocarbon radical having 1 to 6 C atoms;

-NC; -N-SO-aromatics, preferably isocyclic with 6 to 10 C- ^X R " ^l

Atoms, optionally substituted with radicals such as R ../ R ₂ ; or R ₁ , R, = isocyclic or heterocyclic aromatic having 6 to 10 C atoms, optionally substituted by radicals such as R / R ";

however, at least one of R ~ is R, OH or H -W ; R ¹ = as R ₁ / R ₀ ; R "= as R ₁ / R ₀ ; additionally aromatic,

\ Ii IZ

preferably isocyclic having 6 to 10 carbon atoms, optionally substituted by one or more of the following groups corresponding to R./R ", O-saturated hydrocarbon radical having 1

to 8 C atoms, OH, COOH, / ^H ^ . / ^R

-j Zrl Xt) J-V

R ^IV = H or

(R ¹¹¹ ,

R-, R ₀ , R _n = H; saturated hydrocarbon radical having 1 to 8 C atoms, / by

preferably aliphatic hydrocarbon radical having 1 to 6 C atoms; O-saturated hydrocarbon radical having 1 to 8 C atoms, preferably 0-aliphatic hydrocarbon radical having 1 to 6 C atoms;

X = any monovalent anion or anion equivalent.

Furthermore, compounds of the following formula which are derived from phenthiazine are suitable:

in which the individual substituents mean the following:

R., R = H; saturated hydrocarbon radical having 1 to 8 C atoms, preferably aliphatic hydrocarbon radical having 1 to 6 C atoms;

I η rr "·. * .-. '. .-> λ ι Ζ η

R ", Rj. = H; saturated hydrocarbon radical having 1 to 8 carbon atoms, preferably aliphatic hydrocarbon radical having 1 to 6 carbon atoms; OH; O-saturated hydrocarbon radical having 1 to 8 C atoms, preferably O-aliphatic hydrocarbon radical having 1 to 6 C atoms

R '

men; s

R, = OH; xj / R '. -N-SO 2 -Aromat, preferably isocylic with 6 to 10

^N R "'H C atoms, optionally substituted by radicals such as R

ZR ₉ ; L = OH; -N-SO - aromatic, preferably isocyclic, with 6 to 10 C

Atoms, optionally substituted with radicals such as R ₁ / R ₉ , if R, not already represents this substituent; or

Rr, R / - = isocyclic or heterocyclic aromatic having 6 to 10 carbon atoms, optionally substituted with radicals such as R./R "; wherein, however, at least one of R ^ to R, represents OH or contains an -NH group

R '= as R ^ R ₂ ;

R "= as R ₁ ZR- additionally aromatic, preferably isocyclic with 6 to 10 carbon atoms, optionally substituted by one or more groups corresponding to R ₁ ZR ₉ , O-saturated hydrocarbons

' H

hydrogen radical with 1 to 8 C atoms, OH, COOH, "_." / _on "

CUN b (J_tl,

TTT ΎΛ7

(R, R ^iV = H or C ^ Cg-X = any monovalent anion or anion equivalent.

The preparation of these compounds and also typical individual compounds which are suitable for the process according to the invention are described in German Offenlegungsschriften Nos. 29 19 197 and 29 19 258.

The compounds mentioned are expediently applied in solution, preferably in aqueous solution, to the apparatus surfaces, a marked favorable effect being observed already at coverages prior to the first polymerization batch of 0.001 gZm ² , which no longer increases above 1 gZm ² , so that larger coating thicknesses are uneconomical. Preferably, coating thicknesses of 0.01 to 0.5 gZm ^{2 are} used.

It is possible to use mixtures of various of the compounds described in more detail above, which are derived from phenoxazine or phenthiazine, and also, in addition to the compounds mentioned, further substances,

which can improve the durability of the coating can be applied. Particular preference is given to using compounds derived from phenoxazine or phenthiazine, which contain at least one hydrogen atom which is bonded to an oxygen or nitrogen atom, and at -20 to + 200 ^° C., if appropriate in the presence of an aprotic solvent with at least a compound of the following general formula was reacted R -Si-Z ,,., wherein Z = Cl; Br; -0-R ₁ ; -OCOR .., where R. is an alkyl radical having 1 to 4 carbon atoms

is; η = 0 or 1, wherein Z may be the same or different, and

R = a hydrocarbon radical having 1 to 6 C atoms, which optionally carries one or more of the following substituents: F, Cl, Br, -SH, NH "and / or, if more than 1 or 2 C atoms are present in whose carbon chain heteroatoms can be incorporated as follows:

. (C)

with the proviso that the radical R contains no -SH or -NH "groups when Z = Cl and / or Br.

Examples of suitable compounds of the formula R -Si-Z ,. , are in the

η '(,' + -nj

German Offenlegungsschrift 31 49 320, page 13, last paragraph, described in the same document are also more details on the reaction with the compounds derived from phenoxazine or phenthiazine, and the various types of coating the apparatus surfaces apparent. The reaction can take place before or after the coating has taken place. A coating thickness of 0.01 to 3 g / m ² , preferably 0.1 to 1 g / m ² , coated area is used.

The water-soluble, organic, hydroxylated carboxylic acid or its water-soluble salt a) and the further water-soluble reducing agent designated b) are expediently added to the aqueous polymerization liquor prior to the polymerization. It is also possible to add a part of the substances mentioned during the polymerization.

Likewise, prior to each filling of the polymerization mixture, the apparatus surfaces are coated with the compound derived from phenoxazine or phenthiazine. The apparatus surfaces may be moist and need not be dried after coating. If reaction products of the compounds derived from phenoxazine or phenthiazine with compounds of the formula R -Si-Z, _N are used,

η (.4-η,)

can be run with a coating several polymerization approaches or be polymerized continuously.

The process according to the invention exhibits particularly good activity when the polymerization is carried out at a pH of below 7, preferably in the range from 2 to 6. It is suitable for free-radically initiated polymerizations in aqueous suspension, in particular for the preparation of vinyl chloride homo-, co- or graft polymers which contain at least 50% by weight, based on the polymer, of polymerized vinyl chloride units. The novel process is preferably used for the preparation of polymers which contain from 99 to 85% by weight, based on the polymer, of polymerized vinyl chloride units, and is particularly suitable for the homopolymerization of vinyl chloride.

It is polymerized with stirring at temperatures of 35 to 85 ⁰ C, preferably 45 to 75 ⁰ C, polymerized. The inner surfaces of the apparatus in which polymerized, as well as the surfaces of internals, such as stirrers, baffles, etc., should be as smooth as possible. The inventive method can be carried out with good success in an apparatus in which the inner surfaces as well as the internals a comparatively high surface roughness (> 10 microns) and slight damage (scratches, etc.) have as they often occur after prolonged use. The surfaces may consist of common materials such as steel, stainless steel, nickel, enamel or glass. The pressure in the polymerization apparatus is expediently the saturation vapor pressure of the vinyl chloride or the monomer mixture used at the polymerization temperature used, it may also be somewhat above the saturation vapor pressure. This applies to the beginning of the polymerization. As a rule, work is carried out at pressures of 0.5 to about 1.5 MPa. For the polymerization, the known catalysts such as percarbonates or peroxides and suspension stabilizers (protective colloids) such as cellulose derivatives and / or polyvinyl acetates tei'lverseifte and optionally used in addition to the above-described further polymerization in the usual ranges. For the preparation of copolymers or graft polymers vinyl chloride in the presence of known monomers which are copolymerizable with vinyl chloride, such as vinyl acetate, acrylic or methacrylic acid esters, and / or known polymers which are graft polymerizable with vinyl chloride, such as ethylene-vinyl acetate copolymers, polymeric acrylates , polymerized. Further customary additives are described for example in DE-OS 31 49 320, page 26, Ab-

λ η . ,

sentence 3, to page 30, paragraph 3 described, wherein predominantly or exclusively monomer-soluble catalysts are used and the use of water-soluble reducing agent, as described above, is absolutely necessary. It is polymerized in the presence of 0.01 to 0.5 wt .-%, based on monomers, of one or more emulsifiers, if emulsifiers are used at all.

The workup of the ready polymerized mixtures to dry, substantially monomer-free polymer is also carried out by known methods by intensive removal of residual unreacted monomers, decantation of most of the aqueous liquor and drying of the wet polymer.

After emptying the polymerization it needs only to be rinsed with water and is then largely free of coating and ready for a new approach.

As already mentioned, the new process brings a surprisingly strong reduction of wall coverings in the polymerization of vinyl chloride, as it is not achievable when using the known per se individual measures of the combination according to the invention and not with any combination of two individual measures. The beneficial effect goes far beyond what would have been expected to be purely additive when using the three different measures. Even after 30 runs consecutively in the same apparatus, no deposit formation is observed after usual rinsing of the inner walls with water, the walls are completely bare. The new process saves set-up times and thus improves the space-time yield in the polymerization. It is further achieved that no coarse particles which have detached from the apparatus wall contaminate the polymer produced.

The following examples and comparative experiments are intended to explain the invention in more detail:

embodiments

All experiments were carried out in a pressure-resistant reactor with 1 m ³ content of VA steel, which is equipped with a double jacket, an impeller and two baffles. Optionally, after pretreatment of the moist inner surface of the reactor and the impeller stirrer surfaces and baffles, as further described below, an aqueous solution containing 520 dm ³ deionized water, 50 g partially hydrolyzed polyvinyl acetate, 40 g methylhydroxypropyl cellulose and

if appropriate, at least one of the further specified below water-soluble additives, given. The reactor is now closed, the air displaced with gaseous vinyl chloride, 320 kg of vinyl chloride and 300 g of di-2-ethylhexylperoxydicarbonat (65% solution in Aliphaten) filled. With stirring at 170 rpm, the contents of the reactor are heated to 53 ^° C. and kept at this temperature until the pressure originally measured has decreased by 0.4 MPa. This is the case after about 6 hours. During this time, 90% of the vinyl chloride used have converted to polyvinyl chloride. The reactor is then expanded, the remaining monomer removed, cooled, the liquid mixture discharged and the reactor rinsed with water. Thereafter, a polymerization batch is run again as described above. The polymerization mixtures taken from the reactor are subjected to intensive demonomerization by conventional methods, after which the major part of the aqueous liquor is separated from the polymer formed by decantation and the water-moist polymer cake is likewise dried by known processes.

If the inner surfaces as well as the surfaces of the impeller stirrer and the baffles are sprayed with solutions as described below, this treatment is carried out before each new batch, that is after emptying the reactor and simply rinsing with water. After spraying, the reactor is again filled with 520 dm ³ aqueous solution without Zwischentr.ocknung

 The experiments carried out one after the other in the same reactor are ended when a clearly visible deposit appears at the reactor wall, which is completely bare before the start of the series of tests. This is removed and weighed. If no visible surface has formed up to then, the series of approaches after 30 consecutive approaches is also terminated.

Comparative experiment A {blank test)

The procedure is as described above, without treatment of the reactor inner walls and without further additions to the aqueous solution. Already after the first approach, a clearly visible deposit has formed, which

Is removed. He weighs 68 g.

Comparative experiment B

The procedure is as described in Comparative Experiment A, except that in the aqueous liquor before each polymerization, 320 g (= 0.1% by weight,

λ η

withdrawn on monomeric vinyl chloride) dissolved malic acid. After two attempts, a significant deposit has formed, which is removed. He weighs 47 g.

Comparative experiment C

The procedure is as described in Comparative Experiment A, but 32 g (= 0.010 wt .-%, based on monomeric vinyl chloride) of sodium dithionite (Na ₂ S ₂ O ₄ ) are dissolved before each approach in the aqueous liquor. Already after the first approach, a clearly visible deposit has formed, which is removed. He weighs 62 g.

Comparative experiment D

The procedure is as described in Comparative Experiment A, but 320 g (= 0.1 wt .-%, based on monomeric vinyl chloride used) of malic acid and 32 g (= 0.01 wt .-% before each approach in the aqueous liquor. , based on vinyl chloride) Na 2 S 2 C> 4 dissolved. After three attempts, a clearly visible deposit has formed, which is removed. He weighs 46 g.

Comparative experiment E

The procedure is as in Comparative Experiment A, but before each approach, the inner surfaces of the reactor and the surfaces of the impeller stirrer and baffles are sprayed with an aqueous solution containing 0.1 wt .-% of the compound

OH

^L CH

Cl

contains. After five attempts, a clearly visible deposit has formed which is removed. He weighs 40 g. '_.

Comparative experiment F

The procedure is as in Comparative Experiment E, but the aqueous liquor prior to each batch 320 g (= 0.1 wt .-%, based on monomeric vinyl chloride used) added malic acid. After eight attempts, a clearly visible deposit has formed, which is removed. He weighs 54 g.

Comparative Experiment G The procedure is as in Comparative Experiment E, but before each

η r-

Set in the aqueous liquor 32 g (= 0.01 wt .-%, based on monomeric vinyl chloride used) Na ₂ S ₂ O ₄ solved.-After five runs'' has formed a significant deposit, which is removed. He weighs 38 g.

example 1

The procedure is as in Comparative Experiment E, but the aqueous liquor before each approach 320 g (= 0.1 wt .-%, based on monomeric vinyl chloride used) of malic acid and 32 g (= 0.010 wt .-%, based on monomeric vinyl chloride ) Na ₂ S ₂ O ₄ added. After 30 runs, the series of experiments is ended, without a deposit formation is observed on the reactor inner walls.

Example 2

The procedure is as in Comparative Experiment E, but the aqueous liquor before each approach 320 g (= 0.1 wt .-%, based on the monomeric vinyl chloride used) tartaric acid and 8g (= 0.0025 wt .-%, based on vinyl chloride ) Sodium nitrite (NaNO ₂ ) added. After 30 batches, the series of experiments is terminated without a visible deposit on the inner walls of the reactor has formed.

Example 3

The procedure is as in Comparative Experiment A, but before each approach, the moist inner surfaces of the reactor and the surfaces of the impeller stirrer and baffles are sprayed with an aqueous solution, the 0.1 wt .-% of a compound of formula

OH

CH

contains, in addition, before each batch of the aqueous liquor 160 g (= 0.05% by weight, based on monomeric vinyl chloride used) of citric acid and 32 g (= 0.01 wt .-%, based on monomeric vinyl chloride) of tin II chloride added. After 30 batches, the series of experiments is ended without a visible coating has formed on the reactor inner walls.

Example 4

The procedure is as in Comparative Experiment A, but before each approach, the inner surfaces of the reactor and the surfaces of the impeller stirrer and the baffles with a 0.1 wt .-% aqueous solution

IR κ

solution of a compound of the formula

OH

N (C ₂ Hs) ₂

Cl

sprayed. In addition, the aqueous liquor before each approach 320 g (= 0.1 wt .-%, based on monomeric vinyl chloride used) of tartaric acid and 32 g (= 0.01 wt .-%, based on monomeric vinyl chloride) sodium formaldehydsulf oxylat added , After 30 batches, the series of experiments is ended without a visible coating has formed on the reactor inner walls. -

Example 5

The procedure is as described in Comparative Experiment E, but 320 g (= 0.1 wt .-%, based on monomeric vinyl chloride used) of malic acid and 32 g (= 0.01 wt .-% before each approach in the aqueous liquor. , based on monomeric vinyl chloride) dissolved sodium thiosulfate. After 30 runs, the test series is terminated without a visible deposit has formed.

Example 6

The procedure is as in Comparative Experiment A, before each approach, the moist inner surfaces of the reactor and the surfaces of the impeller stirrer and baffles are sprayed with an aqueous solution containing 0.1 wt .-% of a compound of formula

OH

C ₂ H ₅

^L -C, Hs

N (C ₂ Hs) ₂

Cl

contains. In addition, in the aqueous liquor prior to each batch 640 g (= 0.2 wt .-%, based on monomeric vinyl chloride used) 'citric acid and 8 g (= 0.0025 wt .-%, based on monomeric vinyl chloride) dissolved sodium nitrite. After 30 runs, the test series is terminated without a visible deposit has formed.

Claims (7)

invention claim 1. A process for the polymerization of vinyl chloride in aqueous suspension in the presence of at least one oil-soluble, free-radically decomposing catalyst, at least one suspension stabilizer and other polymerization auxiliaries and optionally in the presence of up to 50 wt .-%, based on vinyl chloride, at least one monomer, with Vinyl chloride, copolymerizable or / and of a polymer graft-polymerizable with vinyl chloride, characterized in that the polymerization auxiliaries used are: a) at least one water-soluble, organic, hydroxylated carboxylic acid or its water-soluble salt and b) at least one further water-soluble reducing agent not mentioned under a), wherein the polymerization is carried out in an apparatus whose surfaces which come into contact with the polymerization mixture are coated with at least one compound derived from the phenoxazine or phenthiazine, at least one quinoid cyclohexadiene ring, in the 1,4-position with Substituted 2-N atoms and contains at least one benzene ring, the latter being substituted by at least one -OH group or -NH group. 2. The method according to item 1, characterized in that the polymerization is carried out at a pH below 7. 3. The method according to any one of items 1 or 2, characterized in that is polymerized in the presence of 0.0005 to 0.1 wt .-%, based on the monomers used, of the water-soluble reducing agent mentioned under b). 4. The method according to any one of items 1, 2 or 3, characterized in - that the reducing agent mentioned under b) in aqueous solution forms an anion which contains an oxygen compound of sulfur, nitrogen or phosphorus. 5. The method according to any one of the items 1 or 2, characterized in that is polymerized in the presence of 0.01 to 1 wt .-%, based on the monomers used, of the mentioned under a) organic, hydroxylated carboxylic acid or its salt. 6. The method according to any one of items 1, 2 or 5, characterized in that the mentioned under a) water-soluble, organic, hydroxylated carboxylic acid or its water-soluble salt 2 to 8 carbon atoms 1 to 5 hydroxyl groups and additionally 1 to 3 COOH groups contains, wherein an OH group with a COOH group can form an intramolecular ring ester. 7. The method according to any one of items 1, 2, 3, 4, 5 or 6, characterized in that the compound which is derived from phenoxazine or JPhenthiazin contains at least 1 hydrogen atom which is connected to an oxygen or nitrogen atom and at -20 to +200 ⁰ C, optionally in the presence of an aprotic solvent, with at least one compound of the following general formula has been implemented η (4-n) wherein Z is Cl, Br, -O-R ₁₅ -OCOR ₁ , wherein R _{1 is} an alkyl radical having 1 'to 4 C atoms; η = 0 or 1, where Z may be the same or different; R = hydrocarbon radical having 1 to 6 C atoms, which optionally carries one or more of the following substituents: F, -Cl, Br, -SH, -NH "and / or, if more than 2 C-ethers are present in the Carbon chain heteroatoms may be incorporated as follows CO I 'can (C) -O- (C); (C) -N ""; with the proviso that the rest R no -SH or -N ^ groups when Z = Cl and / or Br. ~ R ~