Process for producing polyamides from aminonitriles

The present invention relates to a new process for the preparation of polyamides from aminonitriles and water at elevated temperature and pressure.

The US 2 245 129 describes a discontinuous two-stage production of polycaprolactam from ω-aminocapronitrile ("ACN") and water at a temperature in the range from 150 to 300 ° C and a special temperature program depending on the amount of water added and a pressure of max. 30 bar. Disadvantages of this process are the long reaction times (20 h in the first stage), the low viscosity of the polycaprolactam obtained and the high content of volatile bases (essentially primary acid amides) compared to a polycaprolactam made from caprolactam.

In DE-C 35 34 817, US 4 568 736 and US 4 629 776 the problems described in US 2 245 129 are partially solved by the use of phosphorus and sulfur-containing catalysts. The use of the above-mentioned catalysts improves the low space-time yield of the process described in US Pat. No. 2,245,129. The volatile base content of all products, which according to the above Process is still too high, so that the polyamides are difficult to process and have a reduced number of carboxyl end groups. Due to the stoichiometric discrepancy between amino and carboxyl end groups, the products of the abovementioned processes show an inadequate degree of polymerization and a slow molecular weight build-up during the heat treatment.

Furthermore, complete separation of the catalysts is practically not possible, so that the chemical and physical behavior of the polymers produced using the catalysts, such as the type and amount of the end groups or kinking behavior during spinning, are adversely affected.

In EP-A 0 479 306, when ACN is reacted with water to give polycaprolactam, it is proposed to continuously remove ammonia and water by relaxing after reaching a reaction temperature of 200 to 260 ° C., and at the same time to add water continuously, the pressure being in the range from 14 to 24 x 10⁶ Pa (14 to 24 bar) is selected.

EP-A 65 291 describes a continuous process for the production of polyamide 66 from dinitriles and diamines. The molecular weight is built up via polycondensation.

Caprolactam does not occur as an intermediate, but it does occur in the polymerization of ACN. Because of the different reaction sequences, it is therefore not possible to transfer the process mentioned in EP-A 65 291 to the present problem.

The present invention is therefore based on the object of providing a process for the preparation of polyamides from aminonitriles which ensures improved hydrolysis of the reactants, in particular the acid amide groups, and thus a higher carboxyl end group content. The molecular weight build-up during the polymerization and the temperability of the product are improved in this way compared to the methods of the prior art.

Accordingly, the present invention relates to a process for producing a polyamide by reacting at least one amionitrile with water, which comprises the following steps:<ul id="ul0001" list-style="none"><li>(1) reacting at least one aminonitrile with water in a molar ratio in the range from 1: 1 to 1:30 at a temperature of 100 to 360 ° C, and a pressure of 6 to 12 x 10⁶ Pa, a reaction mixture being obtained</li><li>(2) further reaction of the reaction mixture at a temperature of 150 to 400 ° C and a pressure which is lower than the pressure in stage 1, the temperature and the pressure being chosen such that a first gas phase and a first liquid or a first solid phase or a mixture of first solid and first liquid phase are obtained, and the first gas phase is separated from the first liquid or the first solid phase or the mixture of first liquid and first solid phase, and</li><li>(3) Mixing the first liquid or the first solid phase or the mixture of the first liquid and the first solid phase with a gaseous or liquid phase containing water at a temperature of 150 to 400 ° C. and a pressure of 0.1 up to 30 x 10⁶ Pa, whereby a product mixture is obtained.</li></ul>

The present invention further relates to a process for producing a polyamide by reacting at least one aminonitrile with water, which comprises the following steps:<ul id="ul0002" list-style="none"><li>(1) reacting at least one aminonitrile with water in a molar ratio in the range from 1: 1 to 1:30 at a temperature of 100 to 360 ° C, and a pressure of 6 to 12 x 10⁶ Pa, a reaction mixture being obtained</li><li>(2) further reaction of the reaction mixture at a temperature of 150 to 400 ° C and a pressure which is lower than the pressure in stage 1, the temperature and the pressure being chosen such that a first gas phase and a first liquid or a first solid phase or a mixture of first solid and first liquid phase are obtained, and the first gas phase is separated from the first liquid or the first solid phase or the mixture of first liquid and first solid phase, and</li><li>(3) Mixing the first liquid or the first solid phase or the mixture of the first liquid and the first solid phase with a gaseous or liquid phase containing water at a temperature of 150 to 400 ° C. and a pressure of 0.1 up to 30 x 10⁶ Pa, whereby a product mixture is obtained.</li><li>(4) post-condensation of the product mixture at a temperature of 200 to 350 ° C and a pressure which is lower than the pressure of stage 3, the temperature and the pressure being chosen such that a second gas phase containing water and ammonia and a second liquid or second solid phase or a mixture of second liquid and second solid phase, each containing the polyamide, are obtained.</li></ul>

In addition, the invention provides a process for the preparation of a polyamide by reacting at least one amino nitrile with water, which comprises the following steps:<ul id="ul0003" list-style="none"><li>(1) reacting at least one aminonitrile with water in a molar ratio in the range from 1: 1 to 1:30 at a temperature of 100 to 360 ° C, and a pressure of 6 to 12 x 10⁶ Pa, a reaction mixture being obtained</li><li>(2) further reaction of the reaction mixture at a temperature of 150 to 400 ° C and a pressure which is lower than the pressure in stage 1, the temperature and the pressure being chosen such that a first gas phase and a first liquid or a first solid phase or a mixture of first solid and first liquid phase are obtained, and the first gas phase is separated from the first liquid or the first solid phase or the mixture of first liquid and first solid phase, and</li><li>(4) post-condensation of the first liquid or first solid phase or the mixture of first liquid and first solid phase at a temperature of 200 to 350 ° C and a pressure which is lower than the pressure of stage 3, the temperature and the pressure are chosen such that a second gas phase containing water and ammonia and a second liquid or second solid phase or a mixture of second liquid and second solid phase, each of which contains the polyamide, be obtained</li></ul> provided.

In principle, all aminonitriles, ie compounds which have both at least one amino and at least one nitrile group, can be used as the aminonitrile. Among these, ω-aminonitriles are preferred, with the latter in particular using ω-aminoalkyl nitriles with 4 to 12 C atoms, more preferably 4 to 9 C atoms in the alkylene radical, or an aminoalkylaryl nitrile with 8 to 13 C atoms, where such are preferred which have an alkyl spacer with at least one carbon atom between the aromatic unit and the amino and nitrile group. Among the aminoalkylaryl nitriles, preference is given in particular to those which have the amino and nitrile groups in the 1,4 position to one another.

Linear ω-aminoalkyl nitriles are more preferably used as the ω-aminoalkyl nitrile, the alkylene radical (-CH₂-) preferably contains 4 to 12 carbon atoms, more preferably 4 to 9 carbon atoms, such as 6-amino-1-cyanopentane (6-aminocapronitrile), 7-amino-1-cyanohexane, 8-amino-1- cyanoheptane, 9-amino-1-cyanooctane, 10-amino-1-cyanononane, particularly preferably 6-aminocapronitrile.

6-aminocapronitrile is usually obtained by hydrogenating adiponitrile by known processes, for example described in DE-A 836,938, DE-A 848,654 or US Pat. No. 5,151,543.

Mixtures of several aminonitriles or mixtures of an aminonitrile with other comonomers, such as, for example, caprolactam or the mixture defined in more detail below, can of course be used.

In a special embodiment, especially if one wants to produce copolyamides, the following mixture is used instead of pure 6-aminocapronitrile:<ul id="ul0004" list-style="none" compact="compact"><li>50 to 99.99, preferably 80 to 90% by weight of 6-aminocapronitrile,</li><li>0.01 to 50, preferably 1 to 30% by weight of at least one dicarboxylic acid selected from the group consisting of aliphatic C.₄-C₁₀-α, ω-dicarboxylic acids, aromatic C₈-C₁₂-Dicarboxylic acids and C₅-C₈-Cycloalkanedicarboxylic acids,</li><li>0 up to 50 preferably 0.1 to 30% by weight of an α, ω-diamine with 4 to 10 carbon atoms,</li><li>0 to 50 preferably 0 to 30% by weight of an α, ω-C₂-C₁₂-Dinitrils as well</li><li>0 to 50 preferably 0 to 30% by weight of an α, ω-C₅-C₁₂-Amino acid or the corresponding lactam,</li></ul> where the sum of the individual weight percentages is 100%.

As dicarboxylic acids, aliphatic C₄-C₁₀-α, ω-dicarboxylic acids, such as, for example, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, preferably adipic acid and sebacic acid, particularly preferably adipic acid, and aromatic C.₈-C₁₂-Dicarboxylic acids such as terephthalic acid and C₅-C₈- Use cycloalkanedicarboxylic acids such as cyclohexanedicarboxylic acid.

As α, ω-diamine having 4 to 10 carbon atoms, tetramethylene diamine, pentamethylene diamine, hexamethylene diamine, heptamethylene diamine, octamethylene diamine, nonamethylene diamine and decamethylene diamine, preferably hexamethylene diamine, can be used.

Furthermore, it is also possible to use salts from the dicarboxylic acids and diamines mentioned, in particular the salt from adipic acid and hexamethylenediamine, so-called AH salt.

As α, ω-C₂-C₁₂Dinitrile is preferably used aliphatic dinitriles, such as 1,4-dicyanbutane (adiponitrile), 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 1,8-dicyanoctane, 1,9-dicyannonane, 1 , 10-dicyandecane, particularly preferably adiponitrile.

If desired, diamines, dinitriles and aminonitriles derived from branched alkylene or arylene or alkylarylenes can also be used.

As α, ω-C₅-C₁₂-Amino acid, 5-aminopentanoic acid, 6-aminohexanoic acid, 7-aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanoic acid, 10-aminodecanoic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid, preferably 6-aminohexanoic acid, can be used.

According to the invention, in a first stage (stage 1) an amino nitrile is heated with water, at a temperature of 100 to 360 ° C, preferably 200 to 350 ° C and in particular at 250 to 300 ° C, a pressure of 6 to 12 x 10⁶ Pa is set. In this stage, pressure and temperature can be coordinated with one another in such a way that a liquid or a solid phase and a mixture of liquid or solid phase and a gaseous phase are obtained.

According to the invention, water is used in a molar ratio of aminoalkyl nitrile to water in the range from. 1: 1 to 1:30, particularly preferably from 1: 2 to 1:10, very particularly preferably from 1: 2 to 1: 4, the use of water in excess, based on the aminoalkyl nitrile used, being preferred.

In this embodiment, the liquid or solid phase or the mixture of liquid and solid phase corresponds to the reaction mixture, while the gaseous phase is separated off. In this step, the gaseous phase can be immediately separated from the liquid or solid phase or the mixture of solid or liquid phase, or the reaction mixture formed within this step can be two-phase liquid-gaseous, solid-gaseous or liquid / solid-gaseous are available. Of course, the pressure and temperature can also be coordinated with one another in such a way that the reaction mixture is single-phase, solid or liquid.

The gas phase can be separated off by using stirred or non-stirred separation tanks or boiler cascades and by using evaporator apparatuses, for example by circulation evaporators or thin-film evaporators, such as by film extruders or by annular disk reactors, which guarantee an enlarged phase interface. Pumping around the reaction mixture or using a loop reactor may be necessary in order to enlarge the phase interface.

Furthermore, the separation of the gas phase can be promoted by adding water vapor or inert gas to the liquid phase.

The pressure is preferably set at a preselected temperature so that it is less than the equilibrium vapor pressure of ammonia, but greater than the equilibrium vapor pressure of the other components in the reaction mixture at the predetermined temperature. In this way, the separation of ammonia in particular can be promoted and thus the hydrolysis of the acid amide groups can be accelerated.

In stage 1, stirred tanks, flow tubes or tank cascades can be used. In a two-phase mode of operation, the use of boilers or a reaction column is preferred, while in a single-phase liquid mode of operation the preferred embodiment is a flow tube provided with packing elements. The use of a tube bundle reactor, optionally equipped with packing elements, is also possible in the first process stage and is particularly advantageous in a two-phase procedure in order to improve the heat exchange and to further reduce the axial backmixing of the reactants.

For example, Raschig rings or Sulzer mixing elements can be used as packing elements to ensure a narrow distribution of the residence time and to limit backmixing.

In a further embodiment, the reactor flows through the first stage from top to bottom, which in turn is preferably provided with packing elements which restrict axial backmixing of the reactants. As a result, the ammonia gas released in the reactor, which predominantly arises immediately after entering the reactor, reaches the gas phase at the top of the reactor in the shortest possible way. The disturbance of the flow profile in the further course of the reactor due to rising gas bubbles or convection is therefore slight.

Concerning. there are no restrictions on the residence time of the reaction mixture in the first stage; however, it is generally selected to range from about 10 minutes to about 10 hours, preferably from about 30 minutes to about 6 hours.

Although there are no restrictions with regard to the conversion of nitrile groups in stage 1, the conversion of nitrile groups in stage 1 is generally not less than approximately 70 mol%, preferably at least approximately 95 mol% and in particular approximately 97 to in particular for economic reasons about 99 mol%, based in each case on the number of moles of aminonitrile used.

The conversion of nitrile groups is usually determined by means of IR spectroscopy (CN valence vibration at 2247 wave numbers), NMR or HPLC, preferably by means of IR spectroscopy.

In a further preferred embodiment, the aminonitrile / water mixture is continuously heated with the aid of a heat exchanger, and the mixture heated in this way is mixed back into a reaction vessel heated to the same temperature, preferably a tube, which may optionally contain internals such as Sulzer mixing elements to avoid being introduced. Of course, the aminonitrile and the water can also be heated separately.

Furthermore, it is not excluded according to the invention, the reaction in stage 1 even in the presence of oxygen-containing phosphorus compounds, in particular phosphoric acid, phosphorous acid and hypophosphorous acid and their alkali metal and alkaline earth metal salts and ammonium salts such as Na₃PO₄, Close₂PO₄, N / A₂HPO₄, Close₂PO₃, N / A₂HPO₃, Close₂PO₂, K₃PO₄, KH₂PO₄, K₂HPO₄, KH₂PO₃, K₂HPO₃, KH₂PO₂ carry out, wherein the molar ratio of ω-aminonitrile to phosphorus compounds in the range from 0.01: 1 to 1: 1, preferably from. 0.01: 1 to 0.1: 1 selects.

Furthermore, it is not excluded to also use known metal oxides, such as titanium dioxide, zirconium oxide, aluminum oxide, lanthanum oxide, magnesium oxide, etc., preferably titanium dioxide for heterogeneous catalysis in the individual process steps in order to promote the conversion, in particular of the nitrile groups. The above-mentioned metal oxides are not used in stage 4, but can be used in stages 1 to 3, the use in stage 1 being preferred.

According to the invention, the reaction mixture obtained in the first stage is stage 2 at a temperature of 150 to 400 ° C, preferably a temperature in the range of 220 to 350 ° C and in particular in the range of 250 to 290 ° C and a pressure which is lower as the pressure in stage 1 continued to be implemented. The pressure in the second stage is preferably at least 0.5 × 10⁶ Pa lower than the pressure in stage 1, the pressure generally being in the range from 0.05 to 5 × 10⁶ Pa lies.

In step 2, the temperature and the pressure are selected such that a first gas phase and a first liquid or first solid phase or a mixture of first liquid and first solid phase are obtained, and the first gas phase from the first liquid or first solid phase or the mixture of first liquid and first solid phase is separated off.

The first gaseous phase, which consists essentially of ammonia and water vapor, is generally removed continuously using a distillation device, such as a distillation column. The organic constituents of the distillate which have possibly also separated out during this distillation, predominantly unconverted aminonitrile, can be completely or partially recycled in stage 1 and / or stage 2.

The residence time of the reaction mixture in stage 2 is not subject to any restrictions, but is generally 10 minutes to 5 hours, preferably 15 minutes to 4 hours.

The product line between the first and second stages may contain packing elements, such as Raschig rings or Sulzer mixing elements, which allow the reaction mixture to be released into the gas phase in a controlled manner.

In stage 3, the first liquid or the first solid phase or the mixture of the first liquid and the first solid phase is mixed with a gaseous or liquid phase which contains water, preferably water or steam. This is preferably done continuously. The amount of water added (as a liquid) is preferably in the range from 50 to 1500 ml, more preferably 100 to 500 ml, in each case based on 1 kg of the first liquid or first solid phase or of the mixture of first liquid and first solid phase. This addition of water primarily compensates for the water losses caused in stage 2 and promotes the hydrolysis of acid amide groups in the reaction mixture. This results in a further advantage of this invention that the mixture of the starting products, as used in stage 1, can only be used with a small excess of water.

The water-containing gaseous or liquid phase is preferably preheated in a heat exchanger before being introduced in stage 3 and then mixed with the first liquid or the first solid phase or the mixture of first solid and first liquid phase. If necessary, mixing elements can be used in the reactor to promote the mixing of the components.

Stage 3 is at a temperature of 150 to 400 ° C and a pressure of 0.1 to 30 x 10⁶ Pa operated.

The pressure and temperature can be matched to one another in such a way that the reaction mixture is single-phase liquid or single-phase solid. In another embodiment, pressure and temperature are chosen so that a liquid or a solid phase or a mixture of solid and liquid phase and a gaseous phase are obtained. In this embodiment, the liquid or solid phase or the mixture of liquid and solid phase corresponds to the product mixture, while the gaseous phase is separated off. In the course of this stage, the gaseous phase can be separated off immediately from the liquid or solid phase or the mixture of solid or liquid phase, or the reaction mixture which forms within this stage can be in two phases, liquid-gaseous, solid-gaseous or liquid / solid-gaseous .

At a preselected temperature, the pressure can be set so that it is less than the equilibrium vapor pressure of ammonia, but greater than the equilibrium vapor pressure of the other components in the reaction mixture at the predetermined temperature. In this way, the separation of ammonia in particular can be promoted and thus the hydrolysis of the acid amide groups can be accelerated.

The apparatus / reactors that can be used in this stage are identical to those in stage 1, as discussed above.

In a preferred embodiment, in the two-phase mode of operation, the reactor flows through the first stage from top to bottom, which in turn is preferably provided with packing elements which restrict axial backmixing of the reactants. As a result, the ammonia gas released in the reactor, which predominantly arises immediately after entering the reactor, reaches the gas phase at the top of the reactor in the shortest possible way. The disturbance of the flow profile in the further course of the reactor due to rising gas bubbles or convection is therefore slight.

The residence time in this stage is also not subject to any restrictions, but for economic reasons it is generally chosen to be in the range from 10 minutes to 3 hours, preferably from 20 to 90 minutes.

The product mixture obtained in stage 3 can then be further processed as described below.

In a preferred embodiment, the product mixture of stage 3 is subjected to a post-condensation in a fourth stage at a temperature of 200 to 350 ° C., preferably a temperature of 220 to 300 ° C. and in particular 250 to 270 ° C. Step 4 is carried out at a pressure which is below the pressure of step 3, and preferably in a range from 5 to 1000 × 10³ Pa, more preferably 10 to 300 x 10³ Pa lies. In this step, temperature and pressure are selected so that a second gas phase and a second liquid or solid phase or a mixture of second liquid and second solid phases which contain the polyamide are obtained.

The post-condensation according to stage 4 is preferably carried out so that the relative viscosity (measured at a temperature of 25 ° C. and a concentration of 1 g polymer per 100 ml in 96% by weight sulfuric acid) of the polyamide has a value in the range of approximately 1.6 to about 3.5.

In a preferred embodiment, any water that may be present can be driven out of the liquid phase by means of an inert gas such as nitrogen.

The residence time of the reaction mixture in stage 4 depends in particular on the desired relative viscosity, the temperature, the pressure and the amount of water added in stage 3.

If stage 3 is operated in a single phase, fillers consisting of, for example, Raschig rings or Sulzer mixing elements, which allow controlled relaxation of the reaction mixture in the gas phase, can be used in the product line between stage 3 and stage 4.

In a further embodiment, step 3 can be dispensed with according to the invention and steps (1), (2) and (4) are carried out to produce the polyamide.

This variant is preferably carried out as follows:

In step 1, at least one aminoalkyl nitrile with an excess of water is brought to a temperature in the range from 250 to 350 ° C., more preferably 270 to 300 ° C. and a pressure of 6 to 12 × 10⁶ Pa is heated, the pressure and temperature being coordinated so that the reaction mixture is in a single-phase liquid, and the conversion of nitrile groups is not less than 95 mol%, more preferably in the range from 97 to 99 mol%, based on the mol. Number of aminoalkyl nitrile used, is, whereby a reaction mixture is obtained.

The reaction mixture is in stage 2 at a temperature in the range of 220 to 300 ° C, more preferably 250 to 270 ° C and a pressure in the range of 1 to 7 x 10⁶ Treated Pa, more preferably 1 to 4 x 10⁶ Pa, the pressure in the second stage being at least 0.5 x 10⁶ Pa is lower than in stage 1. At the same time, the first gas phase formed is separated from the first liquid phase.

The first liquid phase obtained in stage 2 is in stage 3 at a temperature in the range from 220 to 300 ° C., more preferably 250 to 270 ° C. and a pressure in the range from 10 to 300 × 10³ Pa, more preferably approximately atmospheric pressure, the resulting second gas phase, containing water and ammonia, being separated from the second liquid phase. Within this stage, the relative viscosity (measured as defined above) of the polyamide obtained is adjusted to a desired value in the range from approximately 1.6 to approximately 3.5 by selection of the temperature and the residence time.

The second liquid phase thus obtained is then discharged by customary methods and, if desired, worked up.

The process described above, ie the sequence according to the invention of stages (1) to (3) or (1), (2) and (4) or (1) to (4) can either be discontinuous, ie in succession in one reactor, or be carried out continuously, ie in successive reactors at the same time. Of course, it is also possible to carry out part of the stages, for example stages (1) and (2) continuously and the remaining stage (s) discontinuously.

In a further preferred embodiment of the present invention, at least one of the gas phases obtained in the respective stages can be returned to at least one of the preceding stages.

It is further preferred that in stage 1 or in stage 3 or both in stage 1 and in stage 3 the temperature and the pressure are selected such that a liquid or a solid phase or a mixture of liquid and solid phase and a gaseous one Phase are obtained, and the gaseous phase is separated.

Furthermore, chain extension or branching or a combination of both can also be carried out in the context of the method according to the invention. For this purpose, substances known to the person skilled in the art for branching or chain extending polymers are added in the individual stages. These substances are preferably added in stage 3 or 4.

The following substances can be mentioned:

Trifunctional amines or carboxylic acids as crosslinkers. Examples of suitable at least trifunctional amines or carboxylic acids are described in EP-AO 345 648. The at least trifunctional amines have at least three amino groups which are capable of reaction with carboxylic acid groups. They preferably have no carboxylic acid groups. The at least trifunctional carboxylic acids have at least three carboxylic acid groups capable of reaction with amines, which can also be present, for example, in the form of their derivatives, such as esters. The carboxylic acids preferably have no amino groups capable of reacting with carboxylic acid groups. Examples of suitable carboxylic acids are trimesic acid, trimerized fatty acids, which can be produced, for example, from oleic acid and can have 50 to 60 carbon atoms, naphthalene polycarboxylic acids, such as naphthalene-1,3,5,7-tetracarboxylic acid. The carboxylic acids are preferably defined organic compounds and not polymeric compounds.

Amines with at least 3 amino groups are, for example, nitrilotrialkylamine, in particular nitrilotriethanamine, dialkylenetriamines, in particular diethylenetriamine, trialkylenetetramine and tetraalkylenepentamine, the alkylene radicals preferably being ethylene radicals. Dendrimers can also be used as amines. The dendrimers preferably have the general formula I.         (R₂N- (CH₂)_n)₂N- (CH₂)_x-N ((Ch₂)_n-NO₂)₂     (I)    in the<ul id="ul0005" list-style="none"><li>RH or - (CH₂)_n-NO¹₂ With</li><li>R¹ H or - (CH₂)_n-NO²₂ With</li><li>R² H or - (CH₂)_n-NO³₂ With</li><li>R³ H or - (CH₂)_n-NH₂ is</li><li>n has an integer value from 2 to 6 and</li><li>x has an integer value from 2 to 14.</li></ul>

N preferably has an integer value of 3 or 4, in particular 3 and x has an integer value of 2 to 6, preferably 2 to 4, in particular 2. The radicals R can also have the meanings indicated independently of one another. The radical R is preferably a hydrogen atom or a radical - (CH₂)_n-NH₂.

Suitable carboxylic acids are those with 3 to 10 carboxylic acid groups, preferably 3 or 4 carboxylic acid groups. Preferred carboxylic acids are those with aromatic and / or heterocyclic nuclei. Examples are benzyl, naphthyl, anthracene, biphenyl, triphenyl or heterocycles such as pyridine, bipyridine, pyrrole, indole, furan, thiophene, purine, quinoline, phenanthrene, poryphin, phthalocyanine, naphthalocyanine. 3,5,3 ', 5'-biphenyltetracarboxylic acid phthalocyanine, naphthalocyanine, 3,5,5', 5'-biphenyltetracarboxylic acid, 1,3,5,7-naphthalenetetracarboxylic acid, 2,4,6-pyridinetricarboxylic acid, 3, 5,3'5'-bipyridyltetracarboxylic acid, 3,5,3'5'-benzophenone tetracarboxylic acid, 1,3,6,8-acridine tetracarboxylic acid, particularly preferably 1,3,5-benzene tricarboxylic acid (trimesic acid) and 1,2,4,5 -Benzoltetracarboxylic acid. Such compounds are commercially available or can be prepared by the process described in DE-A-4 312 182. When using ortho-substituted aromatic compounds, imide formation is preferably prevented by selecting suitable reaction temperatures.

These substances are at least trifunctional, preferably at least tetrafunctional. The number of functional groups can be 3 to 16, preferably 4 to 10, particularly preferably 4 to 8. Either at least trifunctional amines or at least trifunctional carboxylic acids are used in the processes according to the invention, but no mixtures of corresponding amines or carboxylic acids. However, small amounts of at least trifunctional amines can be contained in the trifunctional carboxylic acids and vice versa.

The substances are present in the amount of 1 to 50 µmol / g polyamide, preferably 1 to 35, particularly preferably 1 to 20 µmol / g polyamide. The substances are preferably present in an amount of 3 to 150, particularly preferably 5 to 100, in particular 10 to 70 μmol / g of polyamide in equivalents. The equivalents relate to the number of functional amino groups or carboxylic acid groups.

Difunctional carboxylic acids or difunctional amines as chain extenders. They thus have 2 carboxylic acid groups that can be reacted with amino groups or 2 amino groups that can be reacted with carboxylic acids. Apart from the carboxylic acid groups or amino groups, the difunctional carboxylic acids or amines contain no further functional groups which can react with amino groups or carboxylic acid groups. They preferably do not contain any further functional groups. Examples of suitable difunctional amines are those which form salts with difunctional carboxylic acids. They can be linear aliphatic, like C_1-14-Alkylenediamine, preferably C_2-6-Alkylenediamine, for example hexylenediamine. They can also be cycloaliphatic. Examples are isophoronediamine, dicycycan, laromin. Branched aliphatic diamines can also be used, for example Vestamin TMD (trimethylhexamethylene diamine, manufactured by Huls AG). In addition, the diamines can be aromatic-aliphatic, for example n-xylylenediamine can be used. The entire amines can each be represented by C_1-12-, preferably C_1-14-Alkyl radicals on the carbon skeleton may be substituted.

Difunctional carboxylic acids are, for example, those which form salts with difunctional diamines. It can be linear aliphatic dicarboxylic acids, which are preferably C_4-20-Dicarboxylic acids are. Examples are adipic acid, azelaic acid, sebacic acid, suberic acid. They can also be aromatic. Examples are isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid and dimerized fatty acids.

The difunctional basic building blocks (c) are preferably used in amounts of 1 to 55, particularly preferably 1 to 30, in particular 1 to 15 μm / g of polyamide.

According to the invention, the product mixture obtained in stage 3 or the second liquid or second solid phase or the mixture of second liquid and second solid phases (from stage 4) which contain the polyamide, preferably a polymer melt, is carried out by customary methods, for example using a Pump out of the reaction vessel. The polyamide obtained can then be prepared according to methods known per se, as described, for example, in DE-A 43 21 683 (p. 3, lines 54 to p. 4, line 3) are described in detail.

In a preferred embodiment, the cyclic dimer content of the polyamide-6 obtained according to the invention can be further reduced by first extracting the polyamide with an aqueous solution of caprolactam and then with water and / or gas phase extraction (described for example in EP-A 28 49 68) subject. The low molecular weight components obtained in this aftertreatment, such as caprolactam and its linear and cyclic oligomers, can be returned to the first and / or second and / or third stage.

The starting monomer or Monomer mixture in all stages can preferably in the fourth stage, customary additives and fillers such as pigments, in particular titanium dioxide (anatase and / or rutile), silicon dioxide and talc, chain regulators such as aliphatic and aromatic carbon and dicarboxylic acids such as propionic acid, acetic acid, benzoic acid, terephthalic acid as well as triacetone diamine, stabilizers such as copper (I) halides and alkali metal halides, nucleating agents such as magnesium silicate or boron nitride, Catalysts such as phosphorous acid and antioxidants are added in amounts in the range from 0.01 to 5, preferably from 0.2 to 2% by weight, based on the amount of monomers used.

The polyamides obtained or according to the invention, in particular polyamide-6 and its copolymers, can be used for the production of fibers and materials.

EXAMPLES

example 1

This example explains the present invention using the example of the implementation of ACN.

The AEG (amino end groups) and CEG (carboxyl end groups) were determined by the method described in WO 95/01389 (p. 6, lines 35 to 7, line 40).

According to Parnas-Wagner, the volatile bases were determined by hydrolysis of the polyamide with HCl, release of the bases with NaOH, subsequent steam distillation (according to Parnas) of the bases released into a receiver with HCl and finally back titration of the excess HCl with NaOH. The difference in volatile bases (in mg NH₃/ kg).

The conversion of nitrile groups was determined by IR spectroscopy using FTIR using the band characteristic of the CN group at 2247 cm^-1 determined.

The relative viscosity (RV) was determined at a temperature of 25 ° C. and a concentration of 1 g of polymer per 100 ml in 96% by weight sulfuric acid.

In all of the experiments listed, the laboratory autoclave was operated discontinuously (3 h, 250 ° C, 10⁵Pa (1bar)) after-condensed (stage 4).

The results and test conditions are shown in Table 1.

Example 2

The test conditions in stages 1 and 2 are given in the table below. The temperature in the fourth stage was 270 ° C., the pressure 10⁵Pa (1 bar) and the residence time 1.5 h. <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="10" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="15.75mm" /><colspec colnum="2" colname="col2" colwidth="15.75mm" /><colspec colnum="3" colname="col3" colwidth="15.75mm" /><colspec colnum="4" colname="col4" colwidth="15.75mm" /><colspec colnum="5" colname="col5" colwidth="15.75mm" /><colspec colnum="6" colname="col6" colwidth="15.75mm" /><colspec colnum="7" colname="col7" colwidth="15.75mm" /><colspec colnum="8" colname="col8" colwidth="15.75mm" /><colspec colnum="9" colname="col9" colwidth="15.75mm" /><colspec colnum="10" colname="col10" colwidth="15.75mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col5" align="left">step 1</entry><entry namest="col6" nameend="col10" align="left">Level 2</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">ACN / H₂0 [mol]</entry><entry namest="col2" nameend="col2" align="left">Time [min]</entry><entry namest="col3" nameend="col3" align="left">T (° C)</entry><entry namest="col4" nameend="col4" align="left">p [bar]</entry><entry namest="col5" nameend="col5" align="left">ACN sales [%]</entry><entry namest="col6" nameend="col6" align="left">Time [min]</entry><entry namest="col7" nameend="col7" align="left">T [° C]</entry><entry namest="col8" nameend="col8" align="left">p [bar]</entry><entry namest="col9" nameend="col9" align="left">RV</entry><entry namest="col10" nameend="col10" align="left">liquid bases [mg NH₃/ kg]</entry></row></thead><tbody valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" align="left">1:6</entry><entry namest="col2" nameend="col2" align="left">200</entry><entry namest="col3" nameend="col3" align="left">250</entry><entry namest="col4" nameend="col4" align="left">90</entry><entry namest="col5" nameend="col5" align="left">97</entry><entry namest="col6" nameend="col6" align="left">240</entry><entry namest="col7" nameend="col7" align="left">252</entry><entry namest="col8" nameend="col8" align="left">36</entry><entry namest="col9" nameend="col9" align="left">2,14</entry><entry namest="col10" nameend="col10" align="left">240</entry></row><row><entry namest="col1" nameend="col10" align="justify">AEG: 65 mmol / kg</entry></row><row><entry namest="col1" nameend="col10" align="justify">CEG: 55 mmol / kg</entry></row><row rowsep="1"><entry namest="col1" nameend="col10" align="justify">AEG / CEG = 1.18</entry></row></tbody></tgroup></table></tables><tables id="tabl0002" num="0002"><img file="EP0922065B1_D0001.tif" /></tables>

Comparative examples

The table below shows the product key figures of products manufactured according to the prior art - example 1 of US 5 109 104 and example 1 of US 2 245 129. <tables id="tabl0003" num="0003"><table frame="all"><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">RV</entry><entry namest="col3" nameend="col3" align="left">CEG [mequ / kg]</entry><entry namest="col4" nameend="col4" align="left">flü. Bases [mg NH3 / kg]</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">US 5,109,104</entry><entry namest="col2" nameend="col2" align="char" char=",">1,76</entry><entry namest="col3" nameend="col3" align="center">19</entry><entry namest="col4" nameend="col4" align="center">1910</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">US 2,245,129</entry><entry namest="col2" nameend="col2" align="char" char=",">1,82</entry><entry namest="col3" nameend="col3" align="center">10</entry><entry namest="col4" nameend="col4" align="center">3150</entry></row></tbody></tgroup></table></tables>