Method for the continuous preparation of polyamide prepolymers

A method for the continuous preparation of a polyamide prepolymer, the viscosity in solution of which is comprised between 0.25 dL/g and 0.70 dL/g, as measured according to ISO 307:2007 in m-cresol at 20° C.,

• said formulated polyamide prepolymer having a weight-average molecular weight (Mn) less than 10,000 g/mol, as determined by calculation from the level of terminal functions determined by potentiometric titration in solution and the functionality of said prepolymers or by NMR assay or by size exclusion chromatography,
• wherein it comprises a step of polycondensation from one or more polyamide precursor monomers, said polycondensation step being carried out in a single extruder comprising at least two co-rotating conveying screws, the said monomer(s) being previously added in solid or liquid form without dissolving in a solvent or in water, and said polycondensation step being carried out without extraction of the products formed, said extruder not having any degassing devices, or of a device for removing the polycondensation by-product(s) formed, consisting of an outlet on the outside at atmospheric pressure, or of an outlet connected to a device making it possible to create a low-pressure zone in the extruder.