Patent ID: 6528614
Filing Date: 2003-03-04
Classification: C08G

Abstract:
A process for the production of polyamide-6 from &egr;-caprolactam, comprising:(a) polymerizing &egr;-caprolactam to polyamide-6 at a temperature above the melting point of polyamide-6, (b) recovering the polymerizate in solid form from polymerization step (a), (c) extracting the solid polymerizate obtained in (b), using a suitable solvent, with removal of non-converted monomer and oligomeric compounds from the polymerizate, (d) separating the extracted polymerizate from the extraction agent, (e) concentrating (by evaporation of the solvent) the solution of non-converted monomer and oligomeric compounds which has resulted from the extraction, (f) recycling of the concentrate obtained in (e) as starting material to the polymerization (a), wherein the polymerization under (a) is carried out in at least two successive steps: (a1) at a temperature between 220 and 285Â° C. and an elevated pressure which remains below the vapour pressure of the reaction mixture supplied, with solvent being discharged via the vapour phase, for such a time that the polymerization process is initiated; and (a2) while letting down the pressure prevailing in (a1) to approximately atmospheric or, if desirable, reduced pressure, the reaction mixture obtained in (a1), further called â€œthe prepolymerizateâ€ , is polymerized further, at a temperature above the melting point of polyamide-6, until the required degree of polymerization is reached.