DE1224505B - Process for the production of polyacrylonitrile - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN # f # PATENT OFFICE

EDITORIAL

Int. Cl .:

C08f

German class: 39 c - 25/01

Number:
File number:
Registration date:
Display day:

M55271IVd / 39c
December 28, 1962
September 8, 1966

It is well known that free radical type catalysts are commonly used in the manufacture of Polyacrylonitrile can be used. That means it will use free radical catalysts Initiation of the polymerization of the monomer, acrylonitrile, to form acrylonitrile polymer used.

Although acrylonitrile polymers obtained in the presence of free radicals as catalysts have been used on a large scale in the manufacture of end products, they have been until now unsuitable for use in molding or pressing operations for the formation of molded articles, since they do not acquire adequate thermoplastic properties even when exposed to temperatures were heated at which decomposition occurs.

A process for the polymerization of acrylonitrile is known in which the polymerization is carried out in the presence of a complex catalyst which has been prepared in a known manner from aluminum or zinc alkyl and an alcoholate or acetylacetonate of chromium or vanadium. The polymerization takes place in the presence of benzene or toluene as a solvent for the monomer or a solvent for the polymer which does not react with the catalyst, for example dimethylformamide. The polymerization is carried out according to this procedure at a temperature between 40 and 80 ⁰ C temperature.

In this known polymerization procedure, however, relatively long polymerization times, for example from 30 to 60 hours, are required, whereby products are obtained which do not have the desired pure white color.

There has now been a process for the production of polyacrylonitrile by solution polymerization of monomeric acrylonitrile in a medium inert towards the monomer at a temperature in the range from 0 to 100 ^° C. in the presence of a catalytic amount of a complex, by reaction of aluminum alkyl with a metal compound in an aromatic one Hydrocarbon found as solvent and aluminum alkyl compound obtained in an inert atmosphere, which is characterized in that the polymerization is carried out in the presence of a complex aluminum alkyl compound obtained by reacting an aluminum trialkyl (A) with a compound (B) of the general formula MOR, in which M a Alkali or alkaline earth metal and R is a lower alkyl radical or a hydrogen atom, in molar proportions

Process for the production of polyacrylonitrile

Applicant:

Monsanto Company, St. Louis, Mo. (V. St. A.)

Representative:

Dr. E. Wiegand and Dipl.-Ing. W. Niemann,

Patent Attorneys, Munich 15, Nussbaumstr. 10

Named as inventor:

Robert Chiang, Durham, N. C. (V. St. A.)

Claimed priority:
V. St. ν. America December 29, 1961
(163 163)

ratios of A: B from 0.5: 3 to 3: 0.5 and with crystallization, isolation and purification of the reaction product has been received.

According to a preferred embodiment, the polymerization in the presence of a complex Aluminum alkyl compound carried out by reacting aluminum triethyl with an alkali alkoxide in benzene.

The process of the invention leads to polyacrylonitrile with improved thermoplastic properties, which is suitable for use in molding and pressing operations.

According to the method of the invention, compared to the known method described receive special benefits. This enables pure white acrylonitrile polymers to be produced Can be deformed well, can be produced in a comparatively very short time. The difficulties facing the Oppose the production of completely white acrylonitrile polymers without serious discoloration be deformed by the heat, which is necessary to soften the polymer are well known.

It should be noted in particular that according to the method according to the invention a pure white Polymer with a molecular weight suitable for molding purposes after only 3 hours of poly-

So merization can be obtained while according to the known method polymerization times of 30 to 60 hours are required.

609 659/413

3 4

In addition, the reaction mixture or the supernatant liquid present invention is in accordance with the method ness a 95 ° / _o by weight conversion of the monomers, ie, the soluble reaction products than obtained for the polymer in only 3 hours, as a catalyst in the polymerization of acrylonitrile in the known method the best conversion does not lead to the production of the novel and is achieved after 40 hours and generally 5 drawn polymers, as they are obtained according to the comparatively low or very low conversion of the invention. Therefore, tongues must be achieved, only products with the crystalline product being isolated and purified, yellowish-white or yellowish color are obtained. Aromatic hydrocarbons that are

The particular and essential advantage of the process position of the catalyst have been used, according to the invention is to be seen in the fact that pure io are benzene, toluene and xylene,
white polymers with high conversion to very The polymerization according to the method of

short time, d. H. about one twelfth of the time the invention is carried out in solution. The porter the known method is required, medium used liquid should be anhydrous and achieved will. be inert to the monomer. Under the

The aluminum trialkyl component of the initiator - 15 many known solvents that this besystem can by the empirical formula: meet conditions and the usually with the through

introduction of acrylonitrile polymerization to the application

/ ^ i, any can be used, e.g. B.

Al - R ₂ dimethylformamide, dimethyl sulfoxide and dimethyl

\ _R .20 acetamide, with dimethylformamide in general

^{3 is} preferred. The amount of in the reaction

in which R ₁ , R ₂ and R ₃ low catalyst needed is not critical; it is alkyl groups with 1 to 5 carbon atoms, but required that they represent a catalytic amount. These compounds are generally known from about 0.1 to 5 ° / ₀ by weight, based of the technically available on the weight, said aluminum triethyl 25 monomers is present.

is most easily available and for this reason the polymerization should take place under anhydrous conditions

is preferred. and in an inert atmosphere, which

The other component of the formula MOR, which can be used, for example, by covering the reaction zone during the formation of the polymerization initiator with gaseous nitrogen, consists of an alkali or can be carried out. The polymerization is with alkaline earth alkoxide or hydroxide. Examples of this. Temperatures in the range from about 0 to 100 ⁰ C are, for. B. sodium ethoxide, potassium methoxide, Na carried out, with temperatures of 25 to 50 ⁰ C trium propoxide, magnesium butoxide and sodium are generally preferred. ^ The polymerization of pentoxide, sodium hydroxide, magnesium hydroxide, can take place at atmospheric pressures or even with potassium hydroxide and calcium hydroxide. 35 lower pressures, although in

The manufacture of the catalyst is not, in some cases, the use of superatmospheric conditions the invention. ric pressures can be useful to the

In particular, the catalyst has been brought into contact with the catalyst by first increasing each of the components. Introduces into an aromatic 40, depending on the temperatures, pressure or hydrocarbon used, in the proportions desired. The reaction will vary in the catalyst concentration, the reaction in an oxygen-free atmosphere and with a space duration of one to several hours. Carried out after temperatures, the completion of the reaction in general, the polydy reaction can take place very quickly. The reaction product obtained from the merizate obtained by precipitation in methanol crystallizes on being quiescent. Polymers with molecular genes can be used to leave the reaction mixture from the weight in the fiber-forming area, ie above the solution of a substance. These crystals form the one of 10,000, produced
Kata used in the method of the invention. The invention is described below with reference to the

lyser. The example required for complete crystal formation is explained in more detail,
borrowed time varies largely depending on 50 _{TT n,,}

on the solvent concentration or tempe-. Manufacture of the catalyst

temperature, however, in general a complete In a filled with gaseous nitrogen

Crystallization is achieved in 4 to 8 hours when the reaction ^{flask, which contained 10 cm 3 of} benzene, reaction mixture was kept at room temperature, 0.34 g of sodium ethoxide (calculated 0.005 mol). The time can be significantly reduced by introducing 55 and 4 cm ^{3 of} a 25% solution of aluminum non-solvent, for example n-heptane, into the triethyl in heptane (calculated 0.0065 mol) aluminum reaction mixture. The miniumtriethyl) introduced. The reaction took place fully - crystals are then taken out of the supernatant liquid. The reaction mixture was recovered by conventional methods and allowed to stand for about 12 hours. During this period or isolated, for example by decanting or 60, fine needle-like crystals of about 1.25 cm fell by filtration. Then one or more lengths are made out of the solution. These crystals were recrystallized from the aroma used by decanting and then carried out two-tier hydrocarbon. times recrystallized in benzene to remove impurities

To remove the novel polymers according to the procedure,
of the invention are only obtained if the previous example

standing crystals obtained as such as catalyst ■■

used in the polymerization of acrylonitrile To that prepared in the above manner

will. The use of the entire catalyst obtained were 50 cm ^{3 of} dry dimethyl

formamide and then 10 cm ³ (8.0 g) 'of acrylonitrile were added. The polymerization was carried out in an inert atmosphere and at 50 ⁰ C. After 3 hours, the ^{reaction was terminated by adding 5 cm 8 of} dilute hydrochloric acid to the reaction mixture. The polymer was obtained by precipitation in methanol. The polymer was then washed with dilute hydrochloric acid, water and methanol and then dried under vacuum. The calculated conversion was 95% with a polymer having a molecular weight of 65,000 and a density of 1.175 at 25 ° C. The polymer was not discolored and had a pure white appearance. Chemical analysis gave the following results in percent by weight: 66.64 carbon, 5.60 hydrogen and 26.54 nitrogen. This corresponds to the calculated composition of polyacrylonitrile in percent by weight, namely 67.88 carbon, 5.70 hydrogen and 26.41 nitrogen.

In order to demonstrate the usefulness of the polyacrylonitrile product prepared according to the invention for deformation, transparent tablets 3.175 mm thick were molded. It was found that a sufficient flowability for the formation of tablets could be obtained by reacting the polymer heated to a temperature up to 93 ⁰ C. This is in marked contrast to the temperature of over 135 ° C required for ordinary polyacrylonitrile obtained by free radical catalysis.

Various solubility determinations were also made on the polymers prepared according to the process of the invention and compared with those of polyacrylonitrile obtained by free radical catalysis. Polymers produced according to the invention could in propylene carbonate at temperatures ranging from 35 to 6O ⁰ C in a very dilute solution, ie less than l ° / ₀ concentration of the polymer can be solved. In contrast, were a temperature of 125 to 13O ⁰ C in the case of prepared by free radical polymerization under the same conditions polyacrylonitrile required.

It was also found that the polymers according to the method of the invention from a 50 ° / ₀ solution of succinonitrile at 50 ⁰ C nipht crystallized, whereas in use polyacrylonitrile at 70 ⁰ C from a very dilute solution of the same solvent crystallized.

When the solubility in acetone was tested, it was found that the polymers prepared according to the invention were insoluble in it.

The differences shown in the physical properties between the acrylonitrile polymers, made by the process of the invention and that by the polymerization process Free radical-made polyacrylonitrile was based on differences in their molecular configurations or their structure. To clarify this, X-ray analyzes were carried out the two polymers carried out, initially flat imaging or plate diffraction diagrams of the polymers were recorded with CuK X-rays filtered through Ni. These Plots were then microphotometrically measured along the diameter of the rings.

Reference is made to the drawing, which graphically shows the X-ray diffraction diagrams of the two polymers plotted together. It is noted that the curve labeled A represents the graph obtained with a polyacrylonitrile obtained by free radical polymerization. The curve labeled B represents the diagram of a polymer which was produced by the polymerization according to the invention. These curves or graphs are obtained by plotting the relative intensity (the fraction of light absorbed by the photographic negative of the X-ray diffraction pattern) versus the radial distance from the center of the diffraction pattern (i.e. the distance in millimeters from the primary X-ray radiation). It can be seen that the polymer (B) prepared according to the invention has a considerably more diffuse or scattering configuration or structure than that of the polyacrylonitrile (A). This is expressed by the sharpness of the reflection (expression used in the Braggian sense) in the (0,2,0) plane and the occurrence of the reflection in the (2,0,0) plane. These differences indicate a considerably larger lateral order in the polymer (A), ie the polymer obtained by free radical polymerization.

Claims (2)

Patent claims: 1. Process for the preparation of polyacrylonitrile by solution polymerization of monomeric Acrylonitrile in a medium inert to the monomer at a temperature in the range from 0 to 100 ° C in the presence of a catalytic amount of a complex, by reaction of Aluminum alkyl with a metal compound in an aromatic hydrocarbon as a solvent and aluminum alkyl compound obtained in an inert atmosphere, characterized in that that the polymerization in the presence of a complex aluminum alkyl compound executes, which by reacting an aluminum trialkyl (A) with a compound (B) of the general formula MOR, in which M is an alkali or alkaline earth metal and R is a lower one Mean alkyl radical or a hydrogen atom, in molar ratios of A: B from 0.5: 3 to 3: 0.5 and crystallizing, isolating and purifying the reaction product is. 2. The method according to claim 1, characterized in that the polymerization is carried out in the presence executes a complex aluminum alkyl compound, which by reaction of aluminum triethyl with an alkali alkoxide in benzene. Considered publications:
German interpretative document No. 1 068 895. 1 sheet of drawings 609 659/413 8.66 © Bundesdruckerei Berlin