DE1495791A1 - Process for making polyamides - Google Patents

Description

Process for making polyamides.

It is known to use anhydrous lactams of o -amino carboxylic acids in the presence alkaline catalysts, such as alkali or alkaline earth metals or their hydrides, Oxides, hydroxides, carbonates and alcoholates become high molecular weight at higher temperatures polymerize linear polyamides anionically. Also the use of alkali compounds of caprolactam and pyrrolidone as catalysts is known.

By adding conventional polymerization accelerators such as isocyanates or those releasing compounds, carbodiimides or cyanamide, e.g. B. after the Process of German patent specification 1 067 p91, or acid derivatives such as benzoyl chloride, Terephthaloyl chloride, etc., can significantly reduce the rate of polymerization increased and / or the polymerization temperature can be lowered.

The prerequisite for the effectiveness of alkaline catalysts is their at least partial reaction with the lactam to form the alkali or alkaline earth compound of the lactam.

The course of this reaction is to a large extent dependent on the basicity of the Catalyst dependent, i.e. with decreasing basicity, the catalyst effect also decreases away. However, strongly basic catalysts have the disadvantage that they are difficult to handle are, partly because of their dangerousness, like the alkali metals or hydrides, partly because of their nature as a crystalline powder with a large surface area favored substantial and rapid absorption of water and carbon dioxide from the atmosphere, as a result of which the catalytic converter effect is severely impaired or even can be canceled entirely.

When using strongly basic catalysts in dissolved form these disadvantages are partially avoided, but due to the solubility conditions only solvents are used that interfere with or prevent polymerization, such as alcohol or water, and must therefore be removed beforehand, why an additional operation is required. This also applies to those used so far Alkali or alkaline earth metal compounds of unsubstituted lactams It has now been found that in the manufacture of polyamides by polymerizers with anhydrous lactams (Earth) alkali-lactam compounds, optionally in the presence of polymerization accelerators, all the difficulties mentioned can be avoided by using alkali or alkaline earth metal compounds of such lactams used, which at least carry an alkyl, cycloalkyl, aralkyl or aryl radical on one carbon atom, or their mixtures, dissolved in inert organic solvents, which the polymerization do not bother.

The alkali and alkaline earth salts of the substituted lactams according to Invention are in contrast to the corresponding salts of unsubstituted lactams easily soluble in inert solvents which do not interfere with the polymerization and therefore do not need to be removed.

The catalysts are conveniently used in amounts of 0.001-10 mol, preferably 0.11-1 mol, optionally together with customary amounts of the above Polymerization accelerator, is used.

Examples of substituted lactams according to the invention are methyl, Dimethyl, ethyl, propyl, cyclohexyl, methyloyclohexyl, benzyl, phenyl and Tolyl pyrrolidone and -Z-caprolactam and the corresponding substitution products of the higher lactams. These substituted lactams can be easily made from the corresponding substituted cycloalkanones over their oximes by Beckmann's Rearrangement can be obtained.

The catalysts to be used according to the invention can be prepared from these Lactams in the usual way by reacting with (earth) alkali metals or their hydrides, -Alcoholates or -amides produced in the melt or in a solvent the gaseous or volatile by-products, such as hydrogen, Alcohols or ammonia. The lactams can be used to a certain extent Excess can be used in order to achieve the most complete implementation possible. This excess can be up to 200 mol% and more.

Examples of inert solvents in which the inventive Catalysts are dissolved, are optionally substituted aromatic hydrocarbons, such as benzene, toluene, xylenes, diethylbenzenes, di (iso) propylbenzenes, anisole, etc., tetra- and decahydronaphthalene, also N-alkyl-substituted lactams, such as N-alkyl-pyrrolidone, -Caprolactam etc., and (cycl4-aliphatic hydrocarbons, such as cyclohexane, hexane, Heptane, octane, etc. or mixtures such as petroleum ether, ligroin, white spirit, etc. Furthermore C-substituted lactams themselves can also be used as solvents, as far as they are liquid at room temperature. In addition, if appropriate, mixtures can also be used different solvents can be used.

The concentrations of the catalyst solutions used can be in wide limits fluctuate. They are expediently between about 1 and about 50 percent by weight. However, higher or lower concentrations are also possible.

To polymerize the lactams are at elevated temperature, im generally at about 100 to about 3000C, in the usual way with the catalysts and optionally used polymerization accelerators mixed, whereupon the polymerization has ended after a short time.

Example 1 226 g -Caprolactam with a water content of 0.025% are melted in the absence of moisture and heated to 1500C. so 4.7 ml of a 0.86 molar solution of the Na compound from an isomer mixture, which consists mainly of y-methylcaprclactam, in a mixture of 60% m- and 40% p-diisopropylbenzene (corresponds to 0.2 mol% Na compound) were added and stirred briefly; then 4 ml of 1,6-hexamethylene diisocyanate (0.4 mol%) are added and also stirred. After 2 minutes the caprolactam has become a solid, colorless Polymerized body, which has an extract content of 5, 3 ß and is in m-cresol no longer solves.

Claims (1)

Claim: Process for producing polyamides by polymerizing anhydrous lactams with (Frd-) alkali-lactam compounds, optionally in the presence of polymerization accelerators, characterized in that one alkali or Brdalkali metal compounds used such lactams, which at least one Carbon atom carry an alkyl, cycloalkyl, aralkyl or aryl radical, or their Mixtures dissolved in inert solvents which do not interfere with the polymerization.