DE1495791C3 - - Google Patents

Description

It is known to use anhydrous, melted ε-caprolactam in the presence of alkaline catalysts, such as alkali or alkaline earth metals, their hydrides, oxides, hydroxides, carbonates and alcoholates or their compounds with caprolactam and pyrrolidone, and in the presence of polymerization accelerators, such as isocyanates or such splitting-off compounds, Carbodiimides, cyanamides or acid derivatives such as benzoyl chloride and terephthaloyl chloride, to polymerize to poly-e-caprolactam (German patent specification 1,067,591, British patent specification 868 808 and 931 394).

A prerequisite for the catalytic effectiveness of alkaline catalysts is at least some of them Reaction with the lactam to form the alkali or. Alkaline earth compound of lactam. The sequence this reaction depends to a large extent on the basicity of the catalysts; with decreasing basicity the catalytic effect also decreases. However, strongly basic catalysts have the disadvantage that they are difficult to use. Some of them, like the alkali metals or hydrides, are dangerous, some of them They favor the substantial and due to their nature as crystalline powder with a large surface rapid uptake of'water and carbon dioxide from the atmosphere, reducing the catalytic effect is severely impaired or even canceled entirely.

When using strongly basic catalysts in dissolved form, these disadvantages become partially avoided, but can here due to the solubility conditions only those solvents, such as alcohols or water, are used, which promote the polymerization disturb or prevent and therefore have to be removed beforehand, including an additional one Operation is required. This also applies to the previously used alkali or alkaline earth metal compounds of caprolactam and pyrrolidone. According to British Patent 924 573 as a catalyst Solutions of lithium aluminum compounds used in the polymerization of ε-caprolactam in aliphatic or aromatic hydrocarbons are difficult because of their flammability to handle.

The difficulties mentioned, which occur when working according to the above prior art, are avoided by the method according to the invention.

The inventive method for the preparation of poly-i-caprolactam by polymerization of anhydrous melted ε-caprolactam in the presence of alkali or alkaline earth metal lactamates as a catalyst and in the presence of polymerization accelerators is characterized in that the catalyst used is a solution of alkali or alkaline earth metal compounds of at least one Carbon atom through an alkyl, cycloalkyl,

ίο Aralkyl or aryl radical substituted ε-caprolactams or pyrrolidones in aromatic, aliphatic or cycloaliphatic hydrocarbons, in N-alkyl-substituted Lactams or mixtures of these solvents.

Examples of the substituted lactams are methyl, Dimethyl, ethyl, propyl, cyclohexyl, methylcyclohexyl, benzyl, phenyl and tolyl pyrrolidone and ■ -ε-caprolactam.

Examples of the solvents are benzene, toluene, xylenes, diethylbenzenes, di (iso) propylbenzenes, tetra and decahydronaphthalene, N-alkyl-pyrrolidones, N-alkyl ^ -Caprolactams, cyclohexane, hexane, heptane, Octane, petroleum ether, ligroin, white spirit and their mixtures.

The catalyst solutions used according to the invention can be replaced by the customary Implementation of the substituted lactams mentioned with (earth) alkali metals or their hydrides, alcoholates or amides can be obtained in the solvents mentioned, the gaseous or highly volatile By-products, such as hydrogen, alcohols or ammonia, can be removed. The C-substituted ones Lactams can be used in a certain excess in order to be as complete as possible

To achieve implementation. This excess can be up to 200 mol percent and more.

The concentrations of the catalyst solutions used can vary within wide limits. They are expediently between about 1 and about 50 percent by weight. However, higher or lower concentrations are also possible. The polymerization is carried out at elevated temperatures known for this purpose, generally from about 100 to about 300 ⁰ C, in the presence of heretofore known PoIymerisationsbeschleunigern in conventional amounts. The amounts of catalyst used in the catalyst solutions used according to the invention are expediently in the customary range from 0.001 to 10 mol percent, in particular in the range from 0.01 to 1 mol percent.

The good solubility of the alkali and alkaline earth metal compounds of the C-substituted, ε-caprolactams and pyrrolidones in the solvents mentioned, which do not interfere with the polymerization and therefore do not have to be removed beforehand, ■ unexpectedly contrasts with the solubility behavior the alkali and alkaline earth metal compounds of unsubstituted ε-caprolactam and des unsubstituted pyrrolidone in the same solvents. The comparative tests also show that the inventive method for completely homogeneous and vesicle-free poly-8-caprolactam while using a slurry of sodium caprolactam in diisopropylbenzene as a catalyst instead of the use according to the invention of a solution of sodium C-methylcaprolactam in Diisopropylbenzene as a catalyst is an inhomogeneous Ροΐν-ε-caprolactam permeated with bubbles

arises, which also has a higher residual monomer content and has greater fluctuations in the relative viscosity value.

example 1

g ε-caprolactam with a water content of 0.025 ° / ₀ are melted under exclusion of moisture and heated to 150 ⁰ C. Then, 4.7 ml of a O, 86molaren solution of Na compound from a mixture of isomers, which consists primarily of y-methylcaprolactam, m- in a mixture of 60 ° / ₀ and 40% p-diisopropylbenzene (corresponding to 0.2 mole percent Na Compound) added and stirred briefly; then 1.4 ml of 1,6-hexamethylene diisocyanate (0.4 mol percent) are added and the mixture is also stirred. After 2 minutes, the caprolactam has polymerized to form a solid, colorless body which has an extract content of 5.3% and no longer dissolves in m-cresol.

Comparative tests ·.

La) 2.5 l of anhydrous diisopropylbenzene and 230 g (10 mol) of crust-free metallic sodium are placed in a dry glass flask. At a temperature of about 105 ° C., 1524 g (12 mol) of anhydrous C-methylcaprolactam (mixture of isomers) are then slowly added dropwise with stirring and passing over dry nitrogen. The sodium dissolves in an exothermic reaction with evolution of _{H 2.} It is stirred until the sodium has completely disappeared. The resulting clear, pale yellowish solution contains about 3 mol of sodium C-methylcaprolactam per kg.

b) 2.26 kg of ε-caprolactam with a water content of 0.02 ° / ₀ are melted with exclusion of moisture and heated to 150 ° C. 16.8 g of hexamethylene diisocyanate-1,6 (0.5 mol percent) are added to the melt with stirring. After a further addition of 13.3 g of the catalyst solution obtained according to la), the polymerization begins and ends after 2 minutes. Sections through the solid polycaprolactam show that the polymer is completely homogeneous and free of bubbles. The residual monomer content of PoIycaprolactams is 4.8 ° / _0th

2.a) 2.5 l of anhydrous diisopropylbenzene and 230 g (10 mol) of crust-free metallic sodium are placed in a dry glass flask. At a temperature of about 105 ^° C., 1358 g (12 mol) of anhydrous caprolactam in the form of a melt of 80 ^° C. are then slowly added dropwise with stirring and passing over dry nitrogen. A voluminous precipitate immediately forms with evolution of H ^ and an exothermic reaction. After adding the entire amount of caprolactam, a paste is formed which can no longer be stirred and still contains some of the metallic sodium. Complete conversion of the sodium cannot be achieved even by post-reaction lasting several hours, since it is evidently coated with the insoluble sodium caprolactam.

b) The polymerization is carried out as indicated under lb), except that 13.3 g of the paste described under 2. a) are used instead of the catalyst solution. Investigations of the polycaprolactam body show that it is inhomogeneous inside and interspersed with fine vesicles. The residual monomer content is 5.6 ° / _0th

■

3. In a tubular reactor caprolactam is continuously polymerized at a temperature of 26O ⁰ C in the presence of 0.15 mole percent cyclohexyl, 0.25 mole percent N-butylacetamide and 0.4 weight percent of the catalyst solution obtained according to a). The polymer obtained has after granulation, extraction of the monomeric components and drying an average relative viscosity (measured in l ° / _o strength m-cresol) of 2.98, wherein the relative viscosity of the individual granules

grains fluctuates between 2.93 and 3.03.

4. The continuous polymerization is carried out as under 3.

. described, carried out, but in place of the

catalyst solution, 0.4 percent by weight of the catalyst slurry obtained according to 2.a) is used. After extraction of the monomeric fractions and drying, the polymer obtained has an average value relative viscosity of 2.89, the relative viscosity of the individual granules between 2.65 and 3.18 fluctuates. The product is therefore much more inhomogeneous than the product under 3.

Claims (1)

Claim: Method of manufacture before! Poly-e-caprolactam by polymerization of the anhydrous melted ε-caprolactam in the presence of Alkali or alkaline earth metal lactamates as a catalyst and in the presence of polymerization accelerators, characterized in that that the catalyst used is a solution of alkali or alkaline earth metal compounds substituted at least one carbon atom by an alkyl, cycloalkyl, aralkyl or aryl radical ε-caprolactams or pyrrolidones in aromatic, aliphatic or cycloaliphatic Hydrocarbons, in N-alkyl substituted lactams or used in mixtures of these solvents. .