Alkali metal lactamate

#The invention relates to a catalyst system solid at room temperature, based on an alkali metal lactamate, to a process for the preparation hereof and to polyamides obtained by anionic polymerization of lactam using this catalyst.

#The application of alkali metal lactamate catalysts in the preparation of polyamides by anionic polymerization has been described frequently and is known, inter alia, from the published Netherlands patent application No. 172751. In it catalyst solutions are described obtained by dissolving .alpha.-pyrrolidone and .epsilon.-caprolactam in a solution of the alkali methanolate in methanol and by subsequently removing the methanol by distillation under reduced pressure at 50.degree. C.

#The disadvantage of this process is that during the removal of the methanol by distillation undesired polymerizations take place in the catalyst solution and methanol residues are left behind in the catalyst, which makes the catalyst less suitable for use during the anionic polymerization of polyamides and unsuitable for the preparation of impact-resistant polyamides according to the so-called Reaction Injection Moulding (RIM) technique.

#Into a 1-liter round-bottom flask provided with a stirrer and a distillation condenser with receiver, 30 g sodium methanolate solution in 90 g methanol, 542.6 g caprolactam and 20 g neopentyl alcohol were introduced. The whole of it was heated up to 125.degree. C. while being stirred. By stepwise lowering of the pressure, alcohol was removed from the mixture by distillation. The final pressure was 10 mm Hg. The distillation was continued until the first few caprolactam crystals wer formed in the condenser.

#The catalyst, solid at room temperature, contained 1.1% (wt) neopentyl alcohol and 0.02% (wt) methanol (determined by gas chromatography.). The content of water-insoluble material (polymer) was <0.1% (wt).

#57.9 g potassium methanolate (97%), 767.8 g .epsilon.-caprolactam and 35 g isopropanol were heated in a rotating film evaporator to 120.degree. C. By lowering the pressure stepwise, alcohol was removed from this mixture by distillation. The final pressure was 10 mm Hg. The distillation was continued until the first caprolactam crystals were formed in the condenser.