DE1720322A1 - Process for polymerizing caprolactam - Google Patents

Description

Process for Polymerizing Caprolactam The invention relates to an improved method for the polymerization of caprolactam, in which by polymerization under high pressure polymers with a very low residual monomer and oligomer content can be obtained.

The production of polycaprolactam is carried out on an industrial scale almost exclusively through so-called hydrolytic polymerisation of caprolactam. Here is caprolactam in the presence of water, water-releasing substances and, if necessary Acids, their salts or acid-releasing substances as polymerization accelerators heated to temperatures above the melting point of caprolactam The conversion However, in the hydrolytic polymerization of caprolactam it is technological Interesting temperature range of 220-200 not completely, so the polymer still contains 6 to 15% low molecular weight fractions. For example, at 250 ° C there are 8 % Caprolactam and 2% ring oligomers of caprolactam in the polycaprolactam.

With most uses for polycaprolactam this interferes The polymer has a high content of monomers and ring oligomers, moldings made of monomer-containing Polycaprolactam stick in the mold and separate the caprolactam when stored for a long time in the form of a white coating. In addition, moldings and threads made of monomeric Polycaprolactam has significantly poorer mechanical properties than such monomer-free products.

For removing monomers and ring oligomers from polycaprolactam various methods have already been proposed. Usually the monomer-containing Polymers purified by multiple extraction with hot water. Here it is required the water-saturated polycaproiactam after extraction at increased Temperature and vacuum drying, extraction and drying are with a significant technical effort connected.

It is also possible to use the low molecular weight fractions in the polycaprolactam to be removed by evaporation at elevated temperature in vacuo.

Numerous devices have been proposed for these processes, in which in principle always molten pole: y'aprolactam as a film on heated surfaces applied with a large surface and in a vacuum of volatile components is released. According to another embodiment of the process, the monomer-containing Polycaprolaqtam melt treated in thin-film evaporators in a vacuum. These procedures for de-lactamization of the polycaprolactam in the melt have the disadvantage that the polymer is not evenly distributed over the heated parts of the apparatus and is discharged from the apparatus again. Therefore condenses in some places the polycaprolactam after, whereby the melting point increases, so that the product solidifies and cracks. In addition, if you stay longer, the de-lactamized Polycaprolactam melt back at elevated temperature monomer, also the cationic Polymerization of caprolactam in the presence of strong acids, their salts or Acid-releasing substances with the exclusion of water do not run with 100% conversion from 'probe'. leads to practically the same state of equilibrium as the hydrolytic one Polymerization.

It has now been found that caprolactam in the presence of water, Polymerization catalysts and / or regulators at temperatures between 120 and 3500C can be converted into polycaprolactam with high conversion if the polymerization is carried out for prints over 2000 at.

According to an advantageous embodiment of the method, polymerized at pressures between 3000 and 4000 atmospheres. At can the polymerization also carried out at far higher pressures with an even greater conversion however, the use of even higher pressures is uneconomical high effort for the necessary devices One can get the high pressures during Maintained throughout the polymerization time. It is particularly beneficial However, caprolactam initially under normal pressure or the autogenous pressure of the water the polymerization temperature to prepolymerize and the polymerization if necessary to finish after removing the water under the high pressures.

The polymerization of the caprolactam at temperatures is preferred Above the melting point of the polycaprolactam carried out so that the polymerization takes place in the liquid phase. However, it is also possible to do the implementation below the melting point of the polymer in the plastic or in the solid state.

The upper limit of the polymerization temperature is that Caprolactam decomposes above 300 and rapidly above 5200C.

The process according to the invention can be discontinuous and continuous be performed. Customary reaction accelerators such as γ-amino acids can be used here z.f3. M ~ aminocaproic acid, salts from dicarboxylic acids and diamines like the salt of adipic acid and hexamethylenediamine as well as strong acids e.g. oxygen acids of phosphorus, hydrohalic acids, sulfuric acid, sulfonic acid, dicarboxylic acid and salts of these acids or substances which split off these acids may be present.

The polymerization mixture can be used to regulate the chain length before or during the polymerization organic monocarboxylic acids such as acetic acid, Propionic acid, butyric acid, stearic acid or dicarboxylic acids such as adipic acid, sebacic acid or diamines such as hexamethylene diamine, octamethylene diamine can be added. These Polymerization catalysts and regulators are used in amounts of 0.05 - 2 mol%, preferably 0.1-0.5 moles based on caprolactam are used.

The polymerization of the caprolactam can be carried out in the presence of inert Fillers or pigments, such as silicon dioxide, titanium dioxide, olas fibers 14r; d asbestos are executed.

According to the process according to the invention, polymers with a monomeric and oligomer content of 2-5, 5 obtained, which for almost all purposes without Post-treatment can be further processed into molded articles, films or fibers.

The parts listed in the examples below refer to unless otherwise stated, on the weight.

Example 1 145 parts of caprolactam, 3.3 parts of aminocaproic acid and 1.5 parts of water are placed in a high-pressure autoclave lined with stainless steel heated in an aluminum insert to 250-2600C (temperature in the heating jacket of the autoclave 270-2800C) and 6 hours in a stream of nitrogen at this temperature and normal pressure polymerized. The mixture is then heated at the same temperature and pressure from 5050 - 3600 atm for 4 hours, cools down to 1000C under the pressure mentioned in the heating jacket of the autoclave. from and leaves to room temperature without further injection of nitrogen cooling down.

It becomes colorless polycaprolactam with a K value of 89 and a Methanol extractable content of 2,4-obtained. The gas chromatographic Analysis of the extract shows that it contains 50% caprolactam and 50% of the mixture the ring oligomers of caprolactam are included. That contains polycaprolactam 32.2 eq / t carboxyl end groups and 32.5 eq / t amino end groups.

Example 2 Under the conditions of Example 1, post-condensation is used of the polycaprolactam under a nitrogen pressure of only 1600-2000 atmospheres Polycondensate with a K value of 77 and a residual extract of 5.8%. The extract consists of 69% caprolctam and 1 ffi of the mixture of ring oligomers of caprolactam.

Example 3 If one works as described in Example 1, but holds In the post-condensation phase, 100-1100 atmospheric N2 pressure is obtained, polycaprolactam is obtained with a K value of 76 and a residual extract content of 8.1 1.

Example 4 Under the conditions of Example 1, but with additional Use of 0.1% phosphorous acid is at a post-condensation pressure of 2200-2600 atü N2 polycaprolactam with a K value of 95 and an extract content of 2.7% obtain. The extract consists of 57% caprolactam and 43% of the mixture of the ring oligomers of caprolactam.

Example 5 If you work as described in Example 4, but apply If the post-condensation pressure is 2000 atmospheres, the K value of the polycaprolactam is 92 and the extract content 7.6%.

Example 6 Under the conditions of Example 4, post-condensation printing from 1000 atm polycaprolactam with a K value of 88 with an extract content of 8.4-9.1 ffi was obtained.

Example 7 Polycaprolactam containing 0.1% water and having a K value of 71 with an extract content of 9% is in a high pressure autoclave under an initial pressure of 100 atü N2 until the temperature in the heating jacket of the autoclave reaches 295 ° C Has. Finally, 2700-3600 atmospheres of nitrogen are injected and kept under this for 4 hours Conditions and cools below 3000 atü down to 1000C.

The polycaprolactam treated in this way has a K value of 56 and contains 4.4% residual extract.

Example 8 In the presence of 0.1% phosphorous acid based on Caprolactam becomes polycaprolactam of K value under the conditions of Example 7 62 and an extract content of 3.9%.

Example 9 To 149 parts of caprolactam and 0.45 part of aminocaproic acid 100 atmospheres of N2 are injected into a high pressure autoclave at room temperature. Afterward it is heated until a temperature of 2850C is reached in the heating jacket of the autoclave is; this sets an internal pressure of 2020 atmospheres. N2 is re-injected, until a pressure of 3600 atm is established, and 4 hours under these conditions held. It is cooled below 3000-3600 atü to 1000C.

It becomes polycaprolactam with a K value of 80 with an extract content of 5.3 ffi received. According to the gas chromatographic analysis, the remaining extract exists from approximately equal parts of caprolactam and the mixture of the ring oligomers of caprolactam.

Example 10 Under the conditions of Example 9, caprolactam with an addition of 3.3 parts of # -aminocaproic acid and 0.3 parts of 50 Xiger phosphorous Acid converted into a polycondensate with a K value of 80 with an extract content of 5.1%.

Claims (2)

Claims 1. A process for the polymerization of caprolactam Temperatures between 120 and 3200C in the presence of water, polymerization catalysts and / or regulators, characterized in that the polymerization under pressure performs over 2000 atmospheres. 2. The method according to claim 1, characterized in that when printing prepolymerized to 80 atmospheres and then polymerization at pressures above 20000C is completed.