DE1195051B - Process for the production of higher molecular weight polyacrylonitrile - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

CO8f

German KL: 39 c- 25/01

Number: 1195 051

File number: D 35219IV d / 39 c

Filing date: January 21, 1961

Display day :. June 16, 1965

It is known to use acrylonitrile optionally together with methyl methacrylate, styrene or vinyl acetate to polymerize in 'dimethylformamide. The dimethylformamide is also a solvent for the monomer as for the polymer. Here, 15 to 45% of acrylonitrile is introduced into dimethylformamide and polymerized to a spinnable solution by means of catalysts at 50 ° C. without stirring. In order to work more profitably, a monomer recovery can be installed. Because of Due to the high transfer constant of dimethylformamide, only polymers can be produced their molecular weights only slightly above the lower, suitable for spinning and below the usual required limit. In order to obtain polymers with a higher molecular weight, the acrylonitrile component must increase. The higher the acrylonitrile content, the higher the molecular weight. Here arise but, due to the deteriorated dissolving power of the reaction mixture acrylonitrile-dimethylformamide, depending on the percentage, yield and comonomers, Large solutions to solid gels or, in the case of pure polyacrylonitrile, suspensions to solid, porous ones Crowds. With higher yields of polymers, no more are produced under normal conditions masses to be moved that are very difficult to process into spinning solutions.

It has been now found a process for the preparation of relatively high molecular weight polyacrylonitrile by polymerization of 35 to 50% ⁿ solutions of acrylonitrile, optionally together with at most 5% of methyl methacrylate or vinyl acetate and styrene, based on acrylonitrile, in dimethyl formamide by means of catalysts at 45 to 55 ⁰ C. found, in which then polymers with the desired molecular weights are obtained in high yields if 4 to 20 hours is polymerized to a mass still to be agitated with a stirrer, which is then gradually diluted with dimethylformamide, so that the consistency with which a thorough mixing is just still possible, is not exceeded, is further polymerized.

The resulting pastes or highly viscous solutions can be continuously poured into a thin-film distillation apparatus process into spinnable solutions. However, further processing is not the subject of the invention.

In the process of the invention, it is necessary to continue the polymerization with Carry out stirring in order to achieve higher yields without the risk of gel formation. the However, polymerization can still be carried out continuously for the production of higher molecular weight Polyacrylonitrile

Applicant:

German Academy of Sciences in Berlin, Berlin-Adlershof, Rudower Chaussee 126

Named as inventor:

Dr. Andreas Hunyar t, Darmstadt;

Manfred Kubanczyk,

Dr. Joachim Ulbricht, Teltow-S'eehof

design according to a stirred tank method that produces very uniform polymers. When using the Comonomers which polymerize in more strongly are also obtained by this continuous method Polymers with constant percentage of comonomers during the polymerization. That Molecular weight of the polymers (measured on 0.5% dimethylformamide solutions in the Ubbelohde viscometer and calculated according to Staudinger), depending on the monomer concentration, amount of catalyst, Temperature and reaction time between 50,000 and 80,000. In the known solution polymerization Molecular weights between 40,000 and 60,000 are achieved, but is usually a molecular weight between 60,000 and 80,000 is required for spinning. The increase in molecular weight around 10,000 units is of crucial importance for the reproducibility of the process, as this guarantees the spinnability of the solutions obtained into fibers with constant good textile properties are given, which is not the case with the known method of solution polymerization was the case.

This progress can be clearly seen when comparing Examples 1 and 1a. You can see that with high conversions (this is what one strives for in technology as far as possible) in the same times, higher yields can be achieved with higher molecular weights.

Example 1

198 g of acrylonitrile, 6 g of vinyl acetate, 6 g of styrene, 390 g of dimethylformamide and 1.5 g of azoisobutyronitrile as a catalyst are introduced into a 1-1 stirred vessel, Washed oxygen-free with pure nitrogen and polymerized at 50 ° C with stirring for 24 hours.

509 580/448

After 8 and 16 hours, 120 g of dimethylformamide are added each time admitted. Samples after 8.16 and 24 hours give polymer yields of 40.0, 61.0 and 72.8% with molecular weights of 77,800, 65,600 and 57,000 (measured as indicated in the text).

The paste formed after 24 hours is stirred in a thin-film distillation in a known manner freed from unreacted monomers under vacuum. Here, the paste is clearly dissolved and can are spun by conventional methods.

Comparative example la

198 g of acrylonitrile, 6 g of vinyl acetate and 6 g of styrene are mixed with 1.5 g of azoisobutyronitrile in 630 g of dimethylformamide placed in a round-bottomed flask, flushed with nitrogen and heated to 50 ° C without stirring polymerized. The samples taken after 8, 16 and 24 hours gave yields of 25.6, 45.4 and 62.6% at molecular weights of 39,500, 37,000 and 34,500. The resulting solution is homogeneous and unclouded.

Example 2

201 g of acrylonitrile and 9 g of methyl methacrylate are mixed with 1.05 g of azoisobutyronitrile in 390 g of dimethylformamide, as indicated in Example 1, Polymerized for 36 hours. After 18 hours, the mixture is diluted with 100 g of dimethylformamide. rehearse after 18 and 36 hours, polymer yields of 57.0 and 77.3% ™ t molecular weights of 77 300 and 69 600. The cloudy, highly viscous solution formed after 26 hours can be mixed with 140 g of dimethylformamide further diluted and spun after recovery of the monomers.

35 Example 3

229 g of acrylonitrile and 11 g of methyl methacrylate are polymerized as in Example 1 with 1.2 g of azoisobutyronitrile in 360 g of dimethylformamide. After 12 V _a hours, the mixture is diluted with 120 g of dimethylformamide and polymerized further at 45.degree. After 24 hours, a yield of 61% and a molecular weight of 80,140 are achieved. The cloudy, highly viscous solution can be processed into a spinnable solution after further dilution as indicated.

Example 4

288 g of acrylonitrile and 12 g of methyl methacrylate are mixed with 2.1 g of azoisobutyronitrile in 300 g of dimethylformamide polymerized as in Example 1. After 4 hours and after 7Va hours diluted with 150 g and 250 g DimethyhOrmamid. The reaction temperature increases after 4 hours 45 ° C. A sample after 48 hours gives a yield of 75% and a molecular weight of 74,300. The cloudy, highly viscous solution can be processed further as in Example 1.

Example5

210 g of acrylonitrile are polymerized with 3 g of urea perhydrate and 5 cm ^{8 of} acetic anhydride as a catalyst in 390 g of dimethylformamide as in Example 1. After 8 hours and after 13 hours, the mixture is diluted with 120 g of dimethylformamide each time. A sample after 24 hours gives a yield of 71% and a molecular weight of 58,200. As indicated, the paste is processed into a spinnable solution.

Example 6

A reaction mixture of 33.5 percent by weight of acrylonitrile, 1.5 percent by weight of methyl methacrylate, 65 percent by weight of dimethylformamide and 0.175 percent by weight of azoisobutyronitrile is placed in a 2 liter storage flask. The storage flask is connected to a jacketed vessel with a length of 30 cm and a capacity of 1200 cm ³ through an outlet opening at the bottom with a tap. The lower end of the reaction vessel is tapered and connected to a 0.39 cm ³ gear pump. A special stirrer takes care of the mixing of the reaction medium. After the reaction mixture and the apparatus have been washed free of oxygen and the reaction vessel has been heated to 50 ° C. by means of a thermostat, the vessel is filled and polymerized for 20 hours while stirring. Then the gear pump is turned on and delivered so quickly that the reaction mixture is renewed once every 20 hours. As much new solution flows from the storage vessel as is removed below. The removed, highly viscous, cloudy solution is either continuously processed into a spinning solution in a monomer recovery system after passing through a dilution stage, or the solution is ^{fed to a second, as described, reaction vessel with a capacity of 1400 cm 3} , into which 17 percent by weight of dimethylformamide is simultaneously added by means of a metering pump, and the monomer recovery only happens after a further 20 hours. The yields and the molecular weights are as in Example 2.

Claims (1)

Claim: Process for the production of higher molecular weight Polyacrylonitrile by polymerizing 35 to 50% solutions of acrylonitrile, if appropriate together with a maximum of 5% methyl methacrylate or vinyl acetate and styrene on acrylonitrile, in dimethylformamide by means of catalysts at 45 to 55 ° C, characterized in that that 4 to 20 hours is polymerized to a still to be agitated mass with a stirrer, which then under gradual Dilute with dimethylformamide so that the consistency at which a thorough mixing is just achieved is still possible, is not exceeded, is further polymerized. Considered publications:
German Auslegeschrift No. 1,066,355;
Fiber research and textile technology, 10 (1959), volume 4, p. 169.