Method for the continuous preparation of formulated polyamide prepolymers

A method for the continuous preparation of a formulated polyamide prepolymer, the formulated polyamide prepolymer having a viscosity in solution of which is comprised from 0.25 dL/g to 0.70 dL/g, as measured according to ISO 307:2007 in m-cresol at 20° C., said the 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 the prepolymers or by NMR assay or by size exclusion chromatography,

• wherein the method comprises a step of polycondensation from one or several polyamide precursor monomers, said the polycondensation step being carried out in a single extruder comprising at least two co-rotating conveying screws, said the monomer(s) being previously added in solid or liquid form without dissolving in a solvent or in water, and said the polycondensation step being carried out without extraction of the by-products formed, and comprising the addition of at least one additive during said the polycondensation step in the extruder,
• said the extruder not having any degassing devices, or any device for removing the polycondensation by-product(s) formed, and the water 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, such as a vacuum pump during the reaction.