Method for the continuous preparation of formulated polyamide prepolymers
A method for continuously preparing a formulated polyamide prepolymer, of which the solution viscosity is from 0.25 dL/g to 0.70 dL/g, as measured according to ISO 307:2007 in m-cresol at 20° C., the method including a step of polycondensation on the basis of one or more polyamide precursor monomers, said polycondensation step being carried out in an extruder comprising at least two co-rotating conveying screws, the at least one monomer being previously fed therein in solid or liquid form without being dissolved in a solvent or in water, and said polycondensation step being carried out without extraction of the water formed during said polycondensation step and comprising the addition of at least one additive during said polycondensation step in the extruder.
1 . 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.
2 . The method according to claim 1 , wherein an average degree of polymerization (DPn) of the resulting formulated polyamide prepolymer is less than 50, as determined from the number average molecular weight (Mn) of the formulated polyamide prepolymer according to the following formula:
DPn=Mn/M 0 [Formula 1]
with
Mn being the number average molecular weight of the formulated polyamide prepolymer, and
M 0 being the number average molecular weight of the monomers.
3 . The method according to claim 1 , wherein the formulated polyamide prepolymer is an aliphatic polyamide.
4 . The method according to claim 3 , wherein the monomer(s) is (are) at least one C6 to C18 monomer.
5 . The method according to claim 3 , wherein the monomer(s) is (are) at least one C6 to C18 C12 monomer.
6 . The method according to claim 3 , wherein the monomer(s) is (are) at least one C6 to C18 C10-C12 monomer.
7 . The method according to claim 2 , wherein the extruder is a twin-screw extruder with two co-rotating conveying screws.
8 . The method according to claim 7 , wherein the polycondensation step is carried out at a temperature comprised from 220 to 340° C.
9 . The method according to claim 8 , wherein the residence time of material in the extruder at the temperature comprised from 220 to 340° C. makes it possible to execute the polycondensation reaction so as to arrive at the desired average degree of polymerization, said the residence time being greater than or equal to 1 minute.
10 . The method according to claim 2 , wherein the extruder is an annular multi-screw extruder comprising at least 6 screws.
11 . The method according to claim 10 , wherein the residence time of the material in the extruder at the temperature comprised from 220 to 340° C. makes it possible to execute the polycondensation reaction so as to arrive at the desired average degree of polymerization, said the residence time being greater than or equal to 1 minute.
12 . The method according to claim 7 , wherein the residence time of the material in the extruder is greater than or equal to 1 minute.
13 . The method according to claim 1 , wherein said the at least one additive is selected from catalysts, fillers, dyes, stabilizers, plasticizers, surfactants, nucleating agents, pigments, whiteners, antioxidants, lubricants, flame retardants, natural waxes, and mixtures thereof.
14 . The method according to claim 1 , wherein the single extruder comprises a main hopper, wherein said the at least one additive is added to said the single extruder in the main hopper.
15 . The method according to claim 1 , wherein the single extruder comprises a main hopper, wherein said the at least one additive is added to said the single extruder after the main hopper.