CA1043941A

CA1043941A - Process for the production of acrylonitrile-vinyl chloride copolymers with improved whiteness

Info

Publication number: CA1043941A
Application number: CA233,817A
Authority: CA
Inventors: Joachim Konig; Carlhans Suling
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1974-08-22
Filing date: 1975-08-20
Publication date: 1978-12-05
Also published as: AT335732B; DE2440269A1; NL7509892A; GB1510714A; BE832573A; JPS5147085A; LU73226A1; DD121115A5; ES440369A1; IE41515L; FR2282436B1; DK135170B; JPS5723691B2; ATA644775A; FR2282436A1; IT1041952B; DK135170C; IE41515B1; DK377875A

Abstract

Abstract of the Disclosure The invention relates to a process for the production of chemically uniform acrylonitrile-vinyl chloride copolymers with improved whiteness and improved thermal stability comprising from 25 to 60 % by weight of actylonitrile and from 40 to 75 % by weight of vinyl chloride and, optionally, up to 15 % by weight of other copolymerised ethylenically unsaturated compounds by emulsion polymerisation using a redox catalyst of persulphate and compounds of sulphurous acid, wherein the ratio by weight of reducing component to oxidising component is at least 4 : 1 and wherein polymerisation is carried out at a pH-value in the range of from 2.5 to 4.

Description

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This invention relates to a process for the production of copolymers comprising from "~5 to 60~ of acrylonitrile and from 40 to 75% of vinyl chloride and, optionally, other copolymeri6able compounds with improved whiten~ss and improved thermal stability.
Acrylonitrile and vinyl chloride coPoly~ers are suitable ~or the production of filaments and fibres, so-calle~ modncrylic fibres. ~n a,ldition to the customary favour-able properties, modacrylic fibres, by virtue oi their chlorine content, are highly ~lameproof which make~ them eminently suitable for use in the manu~acture of wigs~ artifici~l furs, children's clothing, carpets, decorative m~terials, curtaining and covering fabrics, etc.
Several processes for copolymerising acrylonitrile and vinyl chloride by emulsion polymerisation are described in the literature.
The oopolymerisation of acrylonitrile and vinyl chloride is characterised by the difierent reactivity of the mo~omers9 the acrylonitrile being considerably more reactive than the vinyl chloride (S.J. Brandrup and E.~. Immergut, Polymer ~ndbook, Interscience Publ., ~e~ York 1966). Any polymerisation reaction in which the entire monomer mi~ture is introduced at the beginning results in the ~ormatio~ of extremely non-uni~orm products which are unsuitable for use as a fibre material, because, to begin with, polymers rich in acrylonitrile are formed whereas, towards the end o~ the polymerisatio~ reaction, when the concentration of acrylonitrile ~0 decreases, the polymers obtailled are e:tremely rich in vinyl chloride. The i~dividual components o~ the polymer mi~ture Le A 1~ 955 :, ~ - ~

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are not compatible with one another~ and it is not possible to prepare use~ul spinning solutions. In order to obtain chemically uniform polymers with a specific ~N : VC r~tio, polymerisation has to be carried out semi-continuously with a certain monomer ratio AN : VC ad~usted at the beginning of the polymerisation reaction. This monomer ratio is ~ept consta~t by replenishing the Imore quickly consumed acrylo-nitrile and, optionally, other monomeric components and the initiator.
Accordingly, the polymerisation reaction is carried out in the presence o~ an e~cess of vinyl chloride, the total amount o~ vinyl c'~loride generally being added at the beginning of polymerisation. In some cases, however, some of the vinyl chloride may even be added while the polymerisation renction is in progress.
The emulsion polymorisation of acrylonitrlle and Yinyl chloride can be activated with conventicnal water-soluble catalysts~ such a~ persulphates or hydrogen pexoxide.
~owever, in order to obtain an adequate poly~erlsation ~elocity, even at low temperatures, it has proved to be fa~ourable to activate the reaction with redox system~
~uch as, for example3 persulphates together with reducing components such as amines, mercaptans or compounds Or tetravalent-sulphur. It has proved to be particularly ~5 effective to activate polymerisation with persulphates and compou~ds of sulphurous acid, such as pyrosulphiteJ
hydrogen sulphite, sulphite or sulphur dioxide in the form o~ sulphurous~ acid anhydride. According to the prior art, the oxidising and reducing component are used in a substantially equivalent quantitative ratio in cases ~here this redox system is used, or alternatively the oxidising component is used in excess in order to guarantee a uniform Le A 15 955 -2-. ~ . . - .
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polymerisation reaction.
According to E~ample A o~ Canadian Patent Specification No. 704,778 for eYample, 0.~44 parts of potassium persulphate ~nd 0.044 parts of sulphur dLoxide are added at the beginn~ng of polymerisation, whilst another 2.7 parts o~
pota6sium persulphate and 2.7 parts of sulphur dioxide are added durlng polymerisation. In other words, a ratio of exactly 1 : 1 is maintained between persulphate and sulphur dio~ide. In Example 1 of the same Patent Speci~ication, 1.5 parts of potassium persulF~ate and 1.85 parts of sodium bisulphite are used, whereas in Example 2,2.6i parts of potassium sulphate and 2.24 parts of sodium bisulphite are used.
According to East German Patent Specification No.
45,280, 60 parts of potassium persulphate and 20 parts of I . .
- sodium pyrosulphite, i.e. an excess of the oxidising oomponent, are used.
In order to ensure that polymerisatiop i8 u~a~fected by fluctuations in p~, a buffer system i8 frequently ~dded to the polymerisation mixture with a view to ad~usting ~
¢~rtain pH-value. Thus, East Genman Patent Speci~icatio~ No.
45,280 ior example discloses a buffer system of sodium hydroxide and phosphoric acid which is said to adjust the pH to a value of ~rom ~.4 to 4.8.
It is poss.ble by this process to obtain polymers ~rom which iilaments ~nd fibres with favourable textile properties can be obtained. Unfortunately, one disad~antage Or the polymers obtained in this way is their unsatisfactory whiteness and their poor thermal stability, i.e. their low colour stability under the effect of relatively high temperatures, so that stabilisers have to be added during spinnin6 of the polymers. Even thenp the filaments obtained ~L!~ 2~ --3--.- -- ' ~ .

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h~ve a yellowish natural colour.
Attempts have been made to obviate this disadvantage by carrying out polymerisation at low temperatures in the presence of special catalysts. Thus, Japanese Patent Specificution No. 37-8994/1962 relates to a prccess ~Eor the low-temperature polymerisation of acrylonitrile and vinyl chloride with a catalyst system of water-soluble peroxides and di~ydroxy maleic acid, polymers with improved whiteness being obtained. Unfortunately, polymerisation at low 1~ temperatures only allows slow polymerisation velocitie~
and poor volume-time yields so that these processes are not sconomic.
One disadvantage of carrying out polymerisation in the presence of a buffer system is that the concentration of electrolyte in the polymerisation vessel is increased by the buffer system, thus adversely affectin~ the stab~l~ty of the late~. This redueed stability onl~ allows polymerisation up to low polymer contents of the latex if coagulAtion is to be avoided. Coagulation would lead to uneontrollable eonditions for the further eourse o~E polymerisation, would complie~te working up to a considerable extent and would reduce product ; quality.
According to DAS No. 1,224,506, acr~lonitrile homopolymers and copolym~ers contai~ing at least 85% of acrylonitrile are obtained by a process carried out in the manner o~ precipi-tation polymerisation with the reaox system p~rsulphate/
pyrosulphite at a pH-Value of no more than 3.8, the ratio by weight o~E sulphoxy activator to peroxy catalyst being at least 10 : 1. It is possible by this process to obtain polymers with an acrylonitrile content of at least 85~ and a ~ood degree of white~ess.
~owever, the satisfactory outcome of this polymerisation Le A 15 955 _4_ : .1 :
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.' prOCe8S i8 depen~ent upon the adequate solubility i~ w~ter o~ the comonomers i~ order to avoid the ~orm~tion o~
~- heterogeneous, incompatible ~nd unsplnnable polymers. For this reason, the process is not suitable for the productio~
of copolym~rs with acrylonitrile contents of less th~n 8~%
or for the production of copolymers of acrylonitrile with comonomers ~hich, like vinyl chloride for example, arc ~ot sufiiciently soluble in water.
It has now been found that copolymers comprising from 25 to 60~ of acry~nitrile and fr~m 40 to 75~ of vinyl chloride ~nd optionally up to 15~ o~ other copolymerisable compound~
;
- can be obtai~ed with improved whiteness and improved thermal : stability and with a high degreè of chemical unl~ormity by carrylng out the copolymerisation reaction in the manner o~
emulsion polymerisation with a redox system of perqulphate and compounds of sulphurous acid and (1) maintaining a ratio by weight of reducing to oxidising component of at lea~t 4 : 1, and

(2) adjusting the pH to values of from 2.5 to 4 by the addition of acid.
Accordingly, it is an object of this invention to improve the emulsion copolymerisation of acrylonitrile and vinyl chloride and, optionally, other monomers.
It is another ob~ect to provide acrylonitrile/vinyl chloride copolymers with improved whiteness.
Still another ob~ect i9 to provide acrylonitrile/vinyl chloride copolymers which exhibit improved thermal stabilities, ~ A still further ob~ect is the provision of acrylonitrile/
`~ ~inyl chloride copolymers with a high degree of chemical uniformity.
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Other ob~ects will be evident from the description and the Examples.
These ob~ects are accomplished by carrying out the process for the production of an acr~ylonitrile-vinyl chloride copolymer comprising from 25 to 60 ~ by weight of acrylonitrile and ~rom 40 to 75 % by weight of vinyl chloride and optionally up to 15 % by weight of at least one other ethylenically unsaturated compound in copolymerised form by emulsion polymerisation u~ing a redox catalyst of persulphate and compounds of sulphurous acid with the improvement which comprises (1) carrying out the polymerisation with a ratio by weight of - reducing component to oxidising component o~ at lea~t 4 : 1, and ` (2) carrying out the polymerisation at a pH-value of from 2.5 to 4.
; 15 Examples of other copolymerisable ethylenically unsaturated compound~ are vinylidene chloride, vinyl bromide, ~inyl esters such as vinyl acetate, or acrylic acid and methacrylic acid esters such as methyl methacrylate or methyl acrylate. To produce substantially non-infla~mable fibres, it has proved to be particularly favourable to add vinyl bromide which, by ~irtue Jf a synergistic effect, enhances the flameproof properties of the filsments.and fibres according to the invention.
It is also possible to use a copolymerisable comp~unds ionic additives which are intended to improve the dyeability of the filaments and fibres, for example styrene sulphonace, allyl sulphonate, methallyl sulphonate, 2-acrylamido-2-- . methyl propane sulphonate or 2-methacrylamido-2-methyl propane:: sulphonate.

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Perqulphates, e~peci~lly alk~li per3ulphate~, such as pot~ssium, sodium or ammonium persulphate, ~re used as the oxidisi~g component in the process according to the invention.
; The reducing component is ~selected from compounds Or 5 sulphurous acid, such as sulphites, hydrogen sulphites and pyrosulphites, more especially alkali salts or sulphur dioxide ln the form of sulphurous acid anhydride.
- Any strong or medium--strength inorganic or organic acid which is stable in the presence of the redox system may be 10 used as the acid for adJustin~ the p~-Yalue. Acids such as sulphuric acid, nitric acid, phosphoric acid or acetic acid are preferably used.
The polymerisation reaction is carried out in the prosence of prefer~bly anionic emul3ifier~ such a~, for 15 example, alkyl sulphonates or alkyl aryl sulphonates, the - alkyl radicals pre~erably containing from 10 to 14 carbon atoms, sulphuric acid esters, such as for example sodium lauryl sulphate, or sulphosuccinic acid esters, such as for example sodium dioctyl sulpho~uccinate.

A latex Or acrylonitrile-vinyl chloride copolymer may additionally be added to the polymerisation mixture iu ~ order to shorten the induction time of the polymerisatio~
- reaction. A latex~starter of this kind i8 described, for e~ampleJ in German Offenlegungsschrift No. 2,300,7l3.
In one preierred embodiment, the polymerisation reaction is carried out at temperatures in the range of from lo to 50 C
in the absence of presence of heavy metal ions, for example iron ions. It is particularly advantageous to carry out polymerisation at temperatures in the range of from 20 to 30 40 C.

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The process according to the invention yields acrylo-nitrile-vinyl chloride copolymers which are distinguished from polymers obtained by conventional processes by their improved whiteness and improved thermal stability.
Another advantage of the process according to the invention is that latices with a longer pot life and a lower tendency towards coagulation are obtained with it. Accordingly, it is possible by the process according to the invention to produce latices of higher polymer content without any tendency towards coagulation, thus providing for better volume-time yields.
Whereas in conventional processes the tendency towards coagulation readily results in the formation of waste, leads to wall deposits and to blockages, the process according to the invention avoids the danger of undesirable coagulation during the poly~erisation reaction and working - up of the polymers, and hence facilitates working up.
The products obtained are soluble for example in acetone, acetonitrile, dimethyl formamide and dimethyl sulph-oxide. They show improved whiteness and improved thermal stability, both in solid form and in solution, and have only a limited tendency to give off hydrochloric acid, even at elevated temperatures. The polymers can be processed both by wet spinning and by dry spinning to form substantially - non-inflammable fibres and filaments with outstanding tex-tile properties.

.

.

. . .: ~ . ~

The following tests were carried out to demonstrate the improved whiteness and improved colour stability at elevated tem-peratures:
- Test ~a):
The polymer powders were pressed and the pressings tested in accordance with DIN 5033 for their standard colour values X, Y, Z under standard light D 65/2 - normal observer.
The colour intervals ~ EAN were calculated from the standard colour values in accordance with DIN 6174 against barium sulphate as standard.

Test ~b):
5% solutions of the polymer powders in dimethyl form-amide were prepared. The transmission curves of the solutions were measured against dimethyl formamide in a 5 mm cell, and the standard colour values for standard light, D 65/2 - normal observer, were calculated from the curves. The colour intervals EAN were calculated from the standard colour values in accord-ance with DIN 6174 against the solvent as standard.
Test tc):
:
Films (50 to 100 ~m thick) were prepared from the . polymer powders and tempered for 1 hour at 140C. 5% solutions of the films in dimethyl formamide were then prepared. The solutions were tested in the same way as in Test (b).
The process according to the invention is illustrated by the following Examples which are to further illustrate the invention without limiting it and in which parts represent parts by weight.
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~3~t4i 22,300 parts of deionised water, 150 parts of sodium pyrosulphite, 112 parts of sodium lauryl sulphate, 0.1 part of iron(II)ammonium sulphate and 1200 parts of a latex of acry-lonitrile/vinyl chloride copolymer with a 6% solids content, are introduced into a polymerisation autoclave. The oxygen is dis-placed by passing nitrogen over, after which 420 parts of acry-lonitrile and 7100 parts of vinyl chloride are introduced under pressure and a temperature of 30C is adjusted. Polymerisation is initiated by the introduction under pressure of a solution of 10.5 parts of ammonium persulphate and 50 parts of 1 N sulphuric acid in 650 parts of deionised water. Immediately afterwards, 220 parts per hour of acrylonitrile and a solution of 3.0 parts ~;
of ammonium persulphate and 14.3 parts of 1 N sulphuric acid in 185 parts of deionised water, are continuously pumped in. A p~l-value of 3.6 to 3.8 is spontaneously adjusted during polymerisation.
After a polymerisation time of 7 hours, a solids content of 14.5%
is reached, a total of 150 parts of sodium pyrosulphite and 31.5 parts of ammonium persulphate having been used. In other words, the ratio of reducing to oxidising component was 4.76 : 1. The latex is let off from the autoclave, a solution of 25 parts of zinc sulphate and 100 parts of concentrated nitric acid in 2000 parts of deionised water is introduced and the product is pre-cipitated by heating to 90C. Working up gives 3850 parts of a polymer with a chlorine content of 31.80%, a nitrogen content of 10.94% ~AN : VC ratio = 42.6 : 57.4) and a K-value of 61.5 (0.5%
solution in dimethyl formamide at 25C), cf. Pikentscher, Cellulose-chemie 13, 58 (1932).

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The above described colour stability tests were carried out on the polymer with the following results:

Test (a) ~ EAN = 2.2 Test (_) ~ EAN = 2.4 Test (c) ~ EAN = 21.5 Comparison Test 1 For comparison, a polymer was prepared in accordance with DT-OS 2,300,713 at a pH-value of 4.6 and with a ratio of sodium pyrosulphite to ammonium persulphate of 0.70:1, the comparison polymer having a chlorine content of 31.55%, a nitrogen content of 10.99% (AN : VC ratio = 42.8 : 57.1) and a K-value of 68.
The colour stability tests carried out with this polymer produced the following results:

Test (a) ~ EAN = 5-5 Test ~b) ~ EAN = 7 0 Test (c) ~ EAN 29.8 In other words, powders and 5% solutions in dimethyl formamide of ths comparison polymer were more heavily discoloured. Also, the 5% solution of the comparison polymer tempered at 140C was more heavily discoloured than the solution of the Example 1 polymer according to the invention. `~

:
22,300 parts of deionised water, 160 parts of sodium pyrosulphite, 112 parts of sodium lauryl sulphate, 0.1 part of iron~II)ammonium sulphate and 1200 parts of a latex of acyl- -onitrile-vinyl chloride copolymer with a solids content of 5%, - are introduced into a polymerisation autoclave. After nitrogen has been passed over, 420 parts of acrylonitrile and 7100 parts of `
vinyl chloride are introduced under pressure and a temperature of 32C is adjusted. Polymerisation is initiated by introducing . -' ~' ' ' " ' :

~.~43i~4i under pressure a solution of 12.7 parts of a~monlum pex-sulphate and 45 parts o~ 1 N sulphuric ~cîd in 805 parts of deionised water. 200 parts per hour of acrylonitrile and a solution oi 2.7 parts of ammonium persulphate and 9.6 parts of 1 N sulphuric acid in 170 parts Or deionised water are then continuously pumped in. ~ p~I-value of

3.5 to 3.~ is automatically adjusted during polymerisation.
After a polymerisation time of 10 hours, a solids content of 17 % is reached, a total of 160 parts of sodium pyrosulphite and 39~7 parts o~ ammonium per~ulphate having been used.
In other words, the ratio of reducing to oxidising component wa-q 4.03 The latex is released from the autoclave, a solution o~
25 parts of zinc sulphate and 100 parts of concentrated nitric acid in 3000 parts of deionised water is added and the product is precipitated by heating to 90C. Working up gives 4360 parts oi a polymer with a chlorine conte~t of 33.80 %, a nitrogen oontent of 10.29 % (AN : VC ratio _ I
- 39.6 : 60,4) and a K-~alue of 61.0, The colour stability tests carried out on the polymer produced the following results:
Test (a) ~ EAN = 2.7 Test ~b) ~ EAN 2 7 ~est (c~ ~ EAN = 21.9 Comlæarison Test 2 For comparison, a polymer was prepared in accordance with DT-OS 2J300,713 at a pH-value of 4.6 and with a ratio of sodium pyxosulphite to ammonium persulphate of oO60 : 1, the comparison polymex having a chlorine content of 33045~, a nitrogen content of 10.08 ~ (AN ; VC = 39.3 : 60.7) and a ~ alue of 66.o.
Colour stability tests carried out with this polymer Le A 15 ~5 -12-. . . . .
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produced the following results:

Test ~a) ~ EAN = 4 4 Test ~b) ~ EAN = 6.9 Test ~c) ~ EAN = 30.2 In other words, powders and 5% solutions in dimethyl formamide o the comparison polymer were more heavily discoloured. Also, the 5% solution of the comparison polymer tempered at 140C was more heavily discoloured than the solution of the Example 2 polymer according to the invention.

. 22,300 parts of deionised water, 250 parts of sodium :
pyrosulphite, 112 parts of sodium lauryl sulphate, 0.1 part of iron(II)ammonium sulphate and 1200 parts of a latex of acry-lonitrile-vinyl chloride copolymer with a solids content of 5%, are introduced into a polymerisation autoclave. After nitrogen has been passed over, 420 parts of acrylonitrile and 7100 parts of vinyl chloride are introduced under pressure and a temperature of 32C is adjusted. Polymerisation is initiated by the introduc-tion under pressure of a solution of 10.1 parts of potassium per-sulphite and 60 parts of 1 N sulphuric acid in 790 parts of de-ionised water. 200 parts per hour of acrylonitrile and a solu-tion of 2.1 parts of potassium persulphate and 12.8 parts of 1 N
sulphuric acid in 170 parts of deionised water are then continu-ously pumped in. A pH-value of 3.3 was measured during polymer-isation. After a polymerisation time of 7 hours, in which a solids content of 13.5% is reached, a total of 250 parts of sodium pyrosulphite and 24.8 parts of potassium persulphate had been used, in other words the ratio of reducing to oxidis- `
ing component was 10.1:1. The latex is worked up in the same way as in Example 2, giving 3480 parts of a polymer ., . ~ .
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:- - - - . . : ' . -with a chlorine content of 33.55 ~, a nitrogen content of 9.83 % (AN : VC = 38.6 : 61 4) ~nd a K-value o~ 61.5.
Measurement of whiteness produc0d the following results:
Test (a) ~ EA~ = 2.2 Test (b) a E~N = 2.4 EX~IPLE 4 .
22,300 p~rts of deionised water, 150 parts o~ sodium pyrosulphite, il2 parts of sodium lauryl sulphate and 1200 parts oi a latex of acrylonitrile-vinyl chloride copolymer with a 5 ~ solids content are ntroduced into a polymerisation autoclave After nitrogen has been passed over, 420 parts of acrylonitrile and ?100 parts of vinyl chloride are introduced under pressure and a temperature of 30C is adjusted.
The polymerisation reaction is initiated by the introduction under pressure of a solution of 12.7 parts o~ ammonium persulphate and 60 parts o~ 1 N sulphuric acid in 790 parts - of deionised water. 220 parts per hour of acrylonitrile and a solution oi 2.7 parts of ammonium persulphate and 12.8 parts o~ 1 N sulphuric acid in 170 parts o$ deionised water are : 20 then continuously pumped in.. A p~-value of 3.2 to 3.3 was measured during polymerisation. After a polymerisation time of 7 hours, in which a solids content of 1005 % is reached9 a total oi 150 parts of sodium pyrosulphite and 31.6 part~ oi 8mmonium persulphate had been used, in other words ~he ratio of reducing component to oxidising component was 4.75 : 1.
The latex is worked up in the same way as in Example 2, giving 2900 parts of a polymer with a chlorine content of 2~.20 ~, a nitrogen content of 12.91 ~ (AN : VC = 49.6 : 50~4) and a K-value oi 73.
~easurement of whiteness and colour stability produced the follo~ing results:

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10~3~4i Test (a3 ~ EAN ~ 1.9 Test (b) ~ EAN ~ 1.7 Test (c) ~ EA~ = 19.4 Comparison Test 4 For comparison, a polymer was prepared in accordance with DT-OS 2,300,713 at a pE~-~alue of 4,6 and with a ratio of sodium pyrosulphite to potaslsium persulphate o~ o.6 : 1, the comparison polymer haYing a chlorine content of 28.60 ~, a nitrogen content of 12.2~ ~ (AN : VC _ 48.0 : 52.0) and a K-value of 75,5.
Colour stability testing of this polymer produced the following results:
Test (a) ~ EAN = 4~7 Test (b) A EAN = 7-9 Test (c) a EAN = 35 In other words, powders and 5 ~ solutions in dimethyl ~ormamide oi the comparison polymer were mo~e hea~ily di6colouxed. Also, the 5 ~ solut~on of the comparison polymer treated at 140C was more heavily discoloured tha~ the ~olution of the Example 4 polymer according to the inventionO
EX~LE 5 Example 1 i8 repeated with all the component~ used kept constant except for the iron(II)ammonium sulphate which i9 only used in a quantity of 0.05 part. Aiter a polymerisation time of 7 hours, a solids cor.tent o~ 13.0 ~ is reached.
Working up gi~es 3470 parts oi a polymer with a chlorine ccntent of 30.60 ~, a nitrogen content of 11.79 % (AN : VC =
45.4 : 54 6) and a K-value of 64.5.
Colour stability tasts carried out with this polymer produced the following results:
Test (a) ~- E ~ = 1.9 Test (b) ~ EAN = 2.6 Test (c) ~ EAN = 22.4 ~e A 15 9~5 -15-,, ., ~ .
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Com~arison Test 5 Colour stability testing of a polymer for comparison at a pH-value of 4.6 and with a ratio of sodium pyrosulphite to potassium persulphnte o~ 0.53 : 1, this comparison polymer having a cnlorine content of 30.3 ~, a nitrogen content of 11.65 ~ (AN : VC = 45.3 : 54.7) and a K-value o~ 72.0, produced the follvwing results:
Test (a) ~\ EAN = 4-3 Test (b) ~ EAN = 6.9 1~) Test (c) ~ EAN = 29.6 EXU~PLE 6 22,300 parts of deionised water, 150 parts o~ sodium pyrosulphite, 112 parts of sodium lauryl sulphate, 0.1 part of iron(II)ammonium sulphate and 1200 parts of a latex of acrylonitrile-vinyl chloride copolymer with a solids content of 5 %, are introduced into a polymerisation autoolave.
After nitrogen has been passed over, 420 parts o~ acrylonitrile and 7100 parts o~ vinyl chloride are introduced under pressure and a temperature of 32C is ad~usted. Polymerisation is initiated by the introduction under pressure of a solutio~ oi 15.1 ~arts of potassium persulphate and 100 parts of l N
sulphuric acid ln 750 parts o~ deionised water. 200 parts per hour of acrylonitrile ~nd a solution o~ 3.2 parts of potassium persulphate and 21.3 parts of 1 N sulphuric acid in 160 parts of deionised water are then continuously pumped in. After a polymerisation time of 7 hours at a p~ value of 3.3, a total o~ 150 parts o~ sodium pyrosulphite and 37.5 parts of potassium persulphate having been used (ratio o~
reducing component to o~idising component = 4 : 1), a solids content of 18.0 % is reached. Working up in the usual ~ay gi~es 5310 parts of a pol~c-r with a chlorine content of 38,45 ~, a nitrogen content of 7.96 ~ (AN : VC = 30.8 : 69.2) Le A 15 955 -16-~ . . .

~IJ4 and a K-value of 59.
Measurement of the whiteness of this polymer produced the following results:
Test (a) ~ EAN = 4 0 Test (b) ~ EAN = 3.8 EXA~LE 7 23,500 parts of de onisecl wat~r, 160 parts of sodium pyrosulphite, 120 parts of sodium alkyl sulphonate with an average chain length of 14 carbon atoms and 0.05 part of iron(II)-ammonium sulphate, are introduced into a p~lymerisatio~
autoclave, After nitrogen has been passed over, 420 parts of acrylonitri~e and 7100 parts of vinyl chloride are introduced under pressure and a temperature of 25C is adjusted. ~he polymerisation reaction is initiated by the introduction under pressure of a solution of 10.1 parts of ammonium persulphate and 50 parts of 1 N sulphuric acid in 650 parts of deionised water. 200 parts per hour of acrylonitrile and a solution o~
2.9 parts of ammonium persulphate and 14.3 parts of 1 N
sulphuric acid in 185 parts o~ deionised water are then continuously pumped i~. A ~-value of 3.5 is measured during polymerisation. After a polymerisation time oi 6 hours, a solids content of 10.0 % is reached. A total of 160 parts of sodium pyrosul~nite and 27.5 parts o~ ammonium persulphate have been used, in other words the ratio oi reducing component to oxidising component was 5.82 : 1. Working up in the usual way gives 3020 parts of a polymer with a chlori~e content oi 31.15 %, a nitrogen content of 11.40 % (AN : VC _ 43.9 :
56.1) and a ~-value of 71.5.
Measurement of whiteness and cclour stability produced the follol~ing results:
Test ~a) a ~AN = 2.1 Test ~b) ~ EAN = 2.1 Test (c) ~ EAN = 23.
Le A lS 955 -17-.

EXU~IPLE 8 i~3~4~
22,300 parts of deionised water, 150 parts of sodium pyrosulphite, 112 parts of sodium lauryl sulphate~ 0.1 part of iron(II)ammonium sulphate, 60 parts of sodium methallyl sulp~onate alld 1200 parts of a latex of acrylonitrile-vinyl chloride copolymer with a solids content of 6 ~, are introduced into a polymerisation autoclave. After nitrogen has been passed over, 420 ~arts of acrylonitrile and 7100 parts of vinyl chlori~le are introduced under pressure and a temperature of 30C is adjusted. Pvlymerisation is initiated : by the introduction under pressure of a solution of 10.4 parts of a~monium persulphate and 50 parts of 1 N sulphuric acid in 650 parts of deionised water. 200 parts per hour of acrylonitrile and a solution of 3.0 parts of ammonium persulphate and 1~.3 parts of 1 N sulphuric acid in 185 parts of deionised water are then continuously pumped in. A pH-value of 3.5 - 3.7 is measured during polymerisation. A~ter a polymerisation time of 7 hours, a solids content of 13.5 i8 reached. For a total input of 150 parts of sodium pyrosulphite and 31.4 parts oi ammonium persulphate9 the ratio of reducing component to oxidising component was

4.78 : 1. Working up in the usual way gives 3520 parts of a pciy~er wi-th a chlorine content of 33.55 ~, a nitrogen content oi 10.19 % (AN VC = 39~6 : 60.4), a sulphur content of 0.26 ~ and a ~-value of 60.o.
Measurement of whiteness and colour stability produced the following results:
Test (a) a EAN = 2.8 Test (b) 1~ ~AN = 2.8 ~0 Test (c) ~ EAN = 24.0 :

Le A 15 955 -18-.~".. .. ~ . . .. ~ ; .

Claims

WHAT WE CLAIM IS:

In the process for the production of an acrylonitrile-vinyl chloride copolymer comprising from 25 to 60 % by weight of acrylonitrile and from 40 to 75 % by weight of vinyl chloride and optionally up to 15 % by weight of at least one other ethylenically unsaturated compound in copolymerised form by emulsion polymerisation using a redox catalyst of persulphate and compounds of sulphurous acid, the improvement which comprises (1) carrying out the polymerization with a ratio by weight of reducing component to oxidising component of at least 4 : 1, and (2) carrying out the polymerisation at a pH-value of from
2.5 to 4.