DE2318609A1 - LOW MOLECULAR WEIGHT POLYACRYLNITRILE AND METHOD OF MANUFACTURING IT - Google Patents

Description

Bayer Aktiengesellschaft 2318609

Central area of patents, trademarks and licenses

Dn / Wi. 509 Leverkusen. Bayerwerk

Low molecular weight polyacrylonitriles and processes for their preparation

The invention relates to uniform, low molecular weight polymers made from acrylonitrile or a predominant proportion of at least 80% by weight of acrylonitrile and an improved one Process for their manufacture.

High molecular weight acrylonitrile polymers are ideal for production of. Threads and fibers with excellent textile properties. A known disadvantage such polymers, however, is their relatively poor colorability and their unfavorable pill behavior.

To improve the dyeing behavior, it has been proposed to produce copolymers with such monomers which contain dye-affine groups. To be favoured here comonomers are used which have sulfo groups, which increase the affinity for basic dyes, e.g. B. styrene or allyl sulfonates. A disadvantage of this method is the uneven and incomplete incorporation of these sulfonates. For the production of copolymers with a defined Sulfonate content, a relatively large excess of these comonomers must be used, of which only a small proportion into which the copolymer is incorporated (see e.g. fiber research and Textiltechnik, Volume 15_, p. 463 (1964) and Volume jL6_, p. (1965)). To increase the dyeability it has also been proposed to use small amounts of chemically identical or

Le A14932

409844/0490

similar polymers with considerably lower molecular weight or lower K value (for definition of the K value S. Fikentscher, Cellulose-Chemie, 1_3_ (1932) S 58) to be added (see the German Auslegeschrift 1 o6 5 9 75). This procedure lowers the K value the mixture only insignificantly, d. H. the viscosity of the spinning solutions is sufficient for the production of fibers. If one compares a polymer with a narrow molecular weight distribution with a mixture with the same K value, which is mainly a polymer with a slightly higher K value and a smaller proportion of a polymer with Contains a considerably lower K value, it is found that threads from the polymer mixture with equally good others Fiber properties are easier to dye than threads made from the uniform polymer. It was also found that threads from the polymer mixture a much improved powder * hold show as threads from the uniform polymer.

However, a suitable process for the production of such polymer mixtures has hitherto been very lacking for the broader application of these polymer mixtures low molecular weight acrylonitrile polymers. Although there are numerous publications for the production of high molecular weight Acrylonitrile polymers known. However, as described in U.S. Patent 3,488,336, these methods can be used not transferred to low molecular weight acrylonitrile polymers.

In US Pat. No. 2,763,636 a method of polymerization is disclosed of acrylonitrile in aqueous salt solutions, according to which low molecular weights of the polymer through Addition of copper salts are available. Experience has shown, however, that an addition of metal salts leads to the their different valence levels in the activation system intervene, to products that are discolored yellow, continue to discolour when heated and a have lower thermal stability than products that are in

Le A 14932 - 2 -

409844/0490

Absence of such heavy metal salts were produced. In addition, it is shown in U.S. Patent 3,488,336 that such low molecular weight polyacrylonitriles are no longer completely soluble and therefore unusable for production of fibers are.

From US Pat. No. 3,488,336 it is known to use low molecular weight acrylonitrile polymers according to the procedure of Prepare precipitation polymerization in an aqueous medium, with the acrylonitrile in great dilution of o, ol to 0.1 moles per liter at a pH above 4 with persulfates is polymerized as an initiator. With this procedure one obtains low molecular weight acrylonitrile polymers, however, very long reaction times are required and even then only low yields of up to a maximum of 23% of theory are obtained.

It has now been found that uniform low molecular weight polymers made of acrylonitrile or a predominant proportion of produce at least 80 wt .-% of acrylonitrile in a practically quantitative yield and in a significantly improved space-time yield leave if you use acrylonitrile by the procedure of precipitation in very dilute aqueous solution polymerized and as an initiator a redox system from z. B. Potassium persulphate and sodium pyrosulphite are used. The watery one The solution is adjusted to a pH of 1.5-4 by adding acids and contains a colorless complexing agent such as B. polyphosphate, ethylenediaminetetraacetic acid, Nitrilotriacetic acid, tartaric acid, boric acid, sodium fluoride and others, preferably polyphosphate, for complexing Heavy metal salts to avoid discoloration of the polymer.

The invention thus provides uniform low molecular weight polymers of acrylonitrile or a predominant proportion of at least 80% by weight of acrylonitrile with K values of 35-65, which are characterized in that they have molecular weights (number average) of 4500-2o,000 and have low molecular weight non-uniformities of 1.0 to 2.7. 4098 U i / 049 0 Le A 149 32 - 3 -

The invention also relates to a process for the production of these uniform, low molecular weight polymers from acrylonitrile or a predominant proportion of. at least 80% by weight of acrylonitrile according to the precipitation polymerization procedure, which is characterized in that the polymerization is carried out in dilute aqueous solution at pH values of 1.5-4 and in the presence of colorless complexing agents at low acrylonitrile concentrations of 0.1 - 1.5% by weight, based on the reaction mixture, is carried out semicontinuously or continuously with a water-soluble redox catalyst in concentrations of 6-55% by weight , based on the monomer.

The process according to the invention gives polymers with K values of 35-65 (0.5% solution in dimethylformamide at 25 ° C.) or molecular weights of 4500-2o,000 (number average). However, by varying the acrylonitrile and catalyst concentration, it is possible to obtain products with a higher and lower K value or molecular weight.

However, products with K values above 65 are eligible for use Not very suitable for the purposes of the invention because they are in contrast to the polymers according to the invention no or only an insufficient improvement in the colorability and the pill behavior can be achieved.

The polymers according to the invention have a narrow molecular weight distribution and non-uniformities in the Molecular weight from 1.0 to 2.7

where My and M _{n are} the molecular weight mean values determined by cosimetry and osmometry, respectively. The molecular weight distribution of the polymers according to the invention is

Le A 14932 - 4 -

409844/0490

narrower and their unevenness in molecular weight is lower than with polymers that are produced by activation with persulfate alone. These will be inconsistencies found with a molecular weight of approx. 3-4. A narrow molecular weight distribution, as in the case of the invention Polymerizaten is present, is desirable because so the proportion of polymer molecules with a particularly low molecular weight can be kept small. These particularly low molecular weight fractions have a low thermal stability. In this way, they increase the tendency of the polymer to discolor at elevated temperature and impair its properties of the fibers and threads made from it. Due to a narrow molecular weight distribution or a If the molecular weight is not uniform, the thermal stability of the polymer can be increased and counteract the discoloration tendency.

It is essential for the method according to the invention, the polymerization with very low acrylonitrile concentrations of 0.1-1.5% by weight in the aqueous solution and with a relatively high redox catalyst concentration based on acrylonitrile perform. The catalyst concentration should be used when using potassium persulphate / Sodium pyrosulfite as redox system 1.1 - 15% by weight potassium persulfate, based on the monomer, the persulfate: pyrosulfite weight ratio being from 1: 0.25 to 1:25 . To maintain this low acrylonitrile concentration, to achieve good space-time yields and to obtain polymers with a narrow molecular weight distribution it is advantageous to run the reaction semi-continuously or continuously and all components to be metered in at constant temperature in the course of the polymerization. With this procedure one can produce very uniform polymers and avoid high ones at all times Monomer concentrations that would lead to the formation of higher molecular weight polymers.

Le A 14932 - "5 -

409844/0490

The method described can at temperatures of 25 - 95 ° C are carried out, wherein a temperature range of Ho - 7o ° C is particularly favorable in order to achieve on the one hand good space-time yields and also to avoid discoloration of the polymer.

The polymers according to the invention are clearly soluble in solvents customary for acrylonitrile polymers, such as dimethylformamide, Dimethyl sulfoxide etc. and yield down at K values of about 35 clear or only slightly cloudy films which become brittle as the K value decreases. Slight cloudiness do not interfere in use, in particular because they do not after mixing the low polymers with high polymers appear more. Films made from polymers with K values below about 35 are cloudy and very brittle. These Polymers are not suitable as a starting material for the manufacture of acrylic threads.

If the products according to the invention are mixed with acrylonitrile polymers with a high K value (greater than 75), these mixtures can be produced by conventional spinning processes such as wet and dry spinning into threads and fibers with good textile properties, process with excellent colorability and improved pill behavior. In the following example Jai are the polymers of the invention and that Process for their production explained in more detail. The parts given are parts by weight.

Le A 1 * 932 - 6 -

409844/0490

Example 1:

4όο parts are deionized in a polymerization flask Water and U parts 1 η nitric acid added. After passing through nitrogen and sand to 55 ° C. are added dropwise over the course of 5 hours simultaneously and at a constant metering rate the following 4 solutions to:

1) 5.2 parts of potassium persulfate in 750 parts of deionized water

2) 16.0 parts of sodium pyrosulfite in 75o parts of deionized water

3) 15 parts of 0.1% polyphosphate solution, 100 parts an ο, oil% zinc chloride solution and 200 parts deionized water

H) 190 parts of acrylonitrile and 10 parts of methyl acrylate

After the end of the metering, the mixture is subsequently stirred at 55 ° C. for 1 hour, cooled, the precipitated polymer filtered off with suction, washed with water and dried at 50.degree. You get 176 parts of polymer (88% yield) with a K value of 53.3 and a molecular weight M = 11,000. The inconsistency the molecular weight is 2.7. The product is clearly soluble in dimethylformamide and gives a clear, brittle film.

Example 2:

Example 1 is repeated using 95 parts of acrylonitrile and 5 parts of methyl acrylate. 83 parts of polymer are obtained (83% yield) with a K value of 4o, a molecular weight of 6,000 and a non-uniform

Le Ά 1H932 - 7 -

409844/0490

3 2318509

speed with a molecular weight of 2.25. The product is clearly soluble in dimethylformamide and gives a clear, brittle film.

Example 3:

The procedure is as in Example 1, but using 0.4 parts of potassium persulfate, 32 parts of sodium pyrosulfite, 95 parts of acrylonitrile and 5 parts of methyl acrylate. There will be 6ο parts Polymer (60% yield) obtained with a K value of 35.5, a molecular weight M of 5300 and a non-uniformity with a molecular weight of 1.9. The polymer is clearly soluble in dimethylformamide and results in a slightly cloudy,: brittle film.

Example H:

You work as in example 1, but add 1.95 parts of potassium persulfate, 6 parts of sodium pyrosulfite, 95 parts of acrylonitrile and 5 parts of methyl acrylate. There will be 82 parts Polymer (82% yield) obtained with a K value of 62.6, a molecular weight M of 17,000 and a non-uniformity with a molecular weight of 2.6. The polymer is clearly soluble in dimethylformamide and results in a clear film.

Example 5 :

16,000 parts of deionized water and 16o parts of 1 η nitric acid are placed in a polymerization kettle. After nitrogen has been passed through and the mixture is heated to 55 ° C., it is added dropwise at the same time and with over the course of 5 hours constant dosing speed to the following solutions.

Le A 14932 - θ -

409844/0490

1) 2ο8 parts of potassium persulfate in 3o,000 parts of deionized water

2) 6Uo parts of sodium pyrosulfite in 3o,000 parts of deionized water

3) 600 parts of a 0.1% polyphoephate solution, 400 parts an ο, oil% zinc chloride solution and 8,000 parts deionized water

3800 parts of acrylonitrile and 200 parts of methyl acrylate. The mixture is subsequently stirred for 1 hour and worked up as in Example 1.

32oo parts of polymer are obtained (yield 80%). The K value is Uo.7, the molecular weight (number average M) 7,000, the non-uniformity in molecular weight 1.8. The polymer is clearly soluble in dimethylformamide and gives a clear, brittle film.

Example 6:

The following are placed in a polymerization kettle: lo, ooo parts of deionized water, 80 parts of 1 η nitric acid, 28 parts of an 0.1% strength polyphosphate solution, 2 parts of potassium persulfate, 12 parts of sodium pyrosulfite, one part of acrylonitrile and 6 parts of methyl acrylate. The mixture is heated to 55 ° C. under nitrogen and stirred for 1 hour. The following four solutions are then added dropwise over the course of 7 hours, at a temperature of 55 ^° C., at the same time and at a constant metering rate:

1) 72 parts of potassium persulfate in 12,000 parts of deionized water

Le A 149 32 - 9 -

2) 224 parts of sodium pyrosulfite in 12,000 parts of deionized water

3) 200 parts of a 0.1% polyphosphate solution, ₃ 1200 parts of a 0.1% zinc chloride solution and 2800 parts of deionized water

4) 254o parts of acrylonitrile and 134 parts of methyl acrylate

The mixture is subsequently stirred at 55 ° C. for 1 hour and the procedure is as in Example 1 on. 2420 parts of polymer are obtained (yield 86.6%). The K value is 44.5, the molecular weight (Numerical mean M) 85oo and the. Molecular weight non-uniformity 1.8.

The polymer is clearly soluble in dimethylformamide and results in a clear, brittle film.

Example 7:.

The following are placed in a polymerization kettle: 12,000 parts of deionized water, 12o parts of 1 η nitric acid, 42 parts a 0.1% polyphosphate solution, 3 parts potassium persulfate, 18 parts of sodium pyrosulfite, 171 parts of acrylonitrile and 9 parts of methyl acrylate.

The mixture is heated to 55 ° C. under nitrogen and the following 4 solutions are added dropwise at the same time and at a constant dosing speed in 6 hours to:

1) 78 parts of potassium persulfate in 22,500 parts of deionized water

2) 240 parts of sodium pyrosulfite in 22,500 parts of deionized water

Le A 14932 - 10 -

409844 / 0-4 90

3) if so parts of a 0.1% polyphosphate solution, 3,000 parts an o, ol% zinc chloride solution and 600 parts of deionized water

4) 2680 parts of acrylonitrile and 1½ parts of methyl acrylate.

The mixture is stirred for 1 hour at 55 ° C. and worked up as in Example 1. 2520 parts of polymer are obtained (Yield 84.0%). The K value is 50.5, the molecular weight (Numerical mean M) 95oo and the inconsistency in the Molecular weight, 2.15. The product is clearly soluble in dimethylformamide and gives a clear, brittle film.

Example 8:

If Example 7 is repeated with 58.5 parts of potassium persulfate and 180 parts of sodium pyrosulfite, 2,400 parts are obtained Polymer obtained (yield 80.0%). The K value is 58.5, the molecular weight (number average M) 14,7oo, the Molecular weight non-uniformity 2.2. The polymer is clearly soluble in dimethylformamide and gives a clear film.

Example 9:

For testing the colorability and the Pi11 behavior the following mixtures are produced:

a) 65 parts of a copolymer of 95% acrylonitrile and 5% methyl acrylate with a K value of 86 and 35 parts Acrylonitrile polymer of Example 8 with a K value of 58.5.

Le A 14932 - 11 -

409844/0490

bj 65 part »copolymer of 95% acrylonitrile and 5% Acrylic acid methyl ester with a K value of 86 and 35 parts of acrylonitrile polymer of example 7 with the K value .5o, 5.

c) 90 parts of a copolymer of 95% acrylonitrile and 5% methyl acrylate with a K value of 86 and 10 parts Acrylonitrile polymer of Example 6 with a K value of M-4.5.

d) 75 parts of a copolymer of 95% acrylonitrile and 5% methyl acrylate with a K value of 86 and 25 parts of acrylonitrile polymer of example 5 with a K value of 4o, 7.

e) A uniform copolymer of 95% acrylonitrile and 5% methyl acrylate with a K value of 86 was used Comparison.

The polymer mixtures a) to d) and the uniform Polymer e) are dissolved 10% in dimethylformamide and cast to give films of Uo thickness. Movies from the Polymer mixtures a) to d) can be compared to Films from the uniform polymer e) with astrazone dyes color better.

The polymer mixtures are dissolved in dimethylformamide and dry spun. The threads obtained show after drawing and shrinking by boiling in water Textile values given in Table 1.

Test titer tear values Loop tear values (d.tex) p / dtex% elongation -. p / dtex! elongation

a) 4.37 2.32 4o, 6 1.21 14.5

b) 4, o4 2.47 35.4 1.11 12.7

c) 3.44, 2.69, 28.8 1.26 lo, o

d) 3.7o 2.54 36.6 1.28 13.8

e) 4.5o 2.58 46.4 1.58 18.7

Le A 149 32 - 12 -

409844/0490

The tensile strength of threads from the polymer mixtures a) to d) is therefore just as good as that of threads made from the uniform polymer of the comparative experiments θ). The loop elongation, which is a measure of the pilling behavior of the threads, is, however, significantly reduced in the case of the threads made from the polymer blends compared to comparative experiment e) and thus indicates a more favorable pill behavior than in the case of threads made from the uniform copolymer of comparative experiment e).

Le A 14932 - 13 -

409844/0490

Claims (7)

Claims; 1) Uniform, low-molecular-weight polymers made of acrylonitrile or a predominant proportion of at least 80% by weight of acrylonitrile with K values of 35 - 65, characterized by that they have molecular weights (number average) from i + Soo to 2o, ooo and low non-uniformities Am Have a molecular weight of 1.0-2.7. Process for the production of uniform, low molecular weight polymers from acrylonitrile or a predominant proportion of at least 80% by weight of acrylonitrile according to the precipitation polymerization procedure, characterized in that that the polymerization in dilute, aqueous solution at pH values of 1.5-4 and in the presence of colorless Complexing agents at low acrylonitrile concentrations from 0.1 to 1.5% by weight, based on the reaction mixture, with a water-soluble redox catalyst in concentrations of 6-55% by weight, based on the monomer, is carried out semicontinuously or continuously. 3) Method according to claim 2 » characterized in that the polymerization is carried out with a water-soluble redox catalyst composed of persulfate and pyrosulfite. 4) Method according to claim 3, characterized in that the concentration of persulfate is 1.1-15% by weight, based on the monomer, and the weight ratio of persulfate: pyrosulfite is from 1 ι 0.25 to 1 ί 25. 5) Method according to claim 2, characterized in that the polymerization is carried out with polyphosphate as a colorless complexing agent. Le A 14932 - 14 - 409844/0490 6) Method according to claim 2 _? characterized in that the polymerization is carried out at temperatures of 25-95 ° C. 7) Use of polymers according to claim 1 as an additive to acrylonitrile polymers which contain at least 80% by weight of acrylonitrile included and near K values of more than 75. Le A 14932 - 15 - 409844/0490