THERMOPLASTIC COMPOSITION MADE FROM A POLYAMIDE POLYMER OBTAINED FROM A PREPOLYMER AND A CHAIN EXTENDER AND MANUFACTURING METHOD

Abstract

A composition including at least one polyamide polymer obtained from at least one reactive polyamide prepolymer including at least one chain extender (PA.sub.1-All.sub.1-PA.sub.1), the polyamide polymer being prepared at a temperature T.sub.1 no lower than the temperature melting temperature or glass transition temperature of the polymer and having a mean molecular weight Mn.sub.1. The composition has a melt viscosity which can be modulated according to the temperature to which the composition is exposed, wherein the temperature is between T.sub.2 and T.sub.3, T.sub.2 and T.sub.3 being higher than T.sub.1, and the melt viscosity η.sub.2 or η′.sub.3 observed at the temperature T.sub.2 or T.sub.3, respectively, being lower than the melt viscosity η.sub.2 or η.sub.3 of the polyamide polymer, which does not include a chain extender and has the same mean molecular weight Mn.sub.1(PA.sub.1) observed at the same temperature T.sub.2 or T.sub.3. The composition includes one or more polyamides.

Claims

1. A composition, comprising at least one polyamide polymer derived from at least one reactive polyamide prepolymer comprising at least one chain extender (PA.sub.1-All.sub.1-PA.sub.1), said polyamide polymer being prepared at a temperature T.sub.1 greater than or equal to the temperature T.sub.m or T.sub.g of said polymer, determined respectively according to standards ISO 11357-3 and ISO 11357-2, and having an average molecular weight Mn.sub.1, as determined by size exclusion chromatography, wherein said composition has a melt viscosity which can be modulated according to the temperature to which said composition is subjected, said temperature being included from T.sub.2 to T.sub.3, T.sub.2 and T.sub.3 being greater than T.sub.1, and said melt viscosity η′.sub.2 or η′.sub.3 observed respectively at the temperature T.sub.2 or T.sub.3 being less than the melt viscosity η.sub.2 or η.sub.3 of said polyamide polymer, free of chain extender and having the same average molecular weight Mn.sub.1 (PA.sub.1) observed at the same temperature T.sub.2 or T.sub.3, and with: said composition comprising or consisting of one or more polyamides, including random or block copolyamides which are polymers, and which comprise different amide units of formula A/(B).sub.r/(C).sub.s, selected as follows: A is a repeating amide unit chosen from lactams or an amino acid of C.sub.6-C.sub.14, an amide unit X.Y in which X represents at least one diamine, said diamine being chosen from a linear or branched aliphatic diamine, a cycloaliphatic diamine and an aromatic diamine or a mixture thereof, and Y represents at least one dicarboxylic acid, said diacid being chosen from: an aliphatic diacid, a cycloaliphatic diacid and an aromatic diacid, said diamine and said diacid comprising from 4 to 36 carbon atoms; B and C are repeating amide units different than A, optionally present depending on the value of r and s, r=0 or 1, s=0 or 1, said amides units B and C being chosen from the same constituents as for A, on the condition that when r and s=1, then B and C are different, the sum of the units A+B+C being equal to 100% by weight, and said composition comprising or consisting of a polyamide polymer resulting from the polymerization of the reaction product of: a1) at least one prepolymer of said thermoplastic polyamide polymer, bearing n reactive end functions X.sub.1, chosen from NH.sub.2 and —CO.sub.2H with n being 1 to 3, with a2) at least one chain extender Y.sub.1-A′-Y.sub.1, with A′ being a hydrocarbon-based biradical of non-polymeric structure, bearing 2 identical end reactive functions Y.sub.1, reactive by polyaddition with at least one function X of said prepolymer a1), Y.sub.1 is chosen from: oxazine, oxazoline, oxazolinone, oxazinone, imidazoline, epoxy, maleimide, and cyclic anhydride, and said composition being free of reinforcing fibers and also of polymeric chain extender, wherein: A is present in a molar content ranging from 55% to 95%, chosen from x.T units, wherein x is a linear aliphatic C.sub.4 to C.sub.18 diamine, and wherein T is terephthalic acid, B is present in a molar content ranging from 5% to 45%, depending on the T.sub.m of the polyamide based on unit A and B is chosen from x′.T units wherein x′ is chosen from: B1) a branched aliphatic diamine bearing a single methyl or ethyl branch (or branching) and having a main chain length different by at least two carbon atoms compared with the main chain length of the diamine x of said associated unit A, or B2) m-xylylenediamine (MXD) or B3) a linear aliphatic C.sub.4 to C.sub.18 diamine, and C is an optional amide unit different than A and B, chosen from amide units based on a cycloaliphatic and/or aromatic structure or based on x′T as defined for B but with x′ different than x′ for the unit B, and under the condition that the sum of the molar contents of A+B+C is equal to 100%.

2. The composition of claim 1, wherein B corresponds to x′ T with x′ chosen according to option B1).

3. The composition of claim 1, wherein B corresponds to x′ T with x′ chosen according to option B2), x′ being MXD.

4. The composition of claim 1, wherein B corresponds to a linear aliphatic diamine according to option B3).

5. The composition of claim 1, wherein: A is x.T, x being a C.sub.4 to C.sub.18 linear aliphatic diamine, B corresponds to x′.T with x′ being B3) a C.sub.4 to C.sub.18 linear aliphatic diamine, and C is present and chosen from: C.sub.6 to C.sub.12 amino acids or lactams, or mixtures thereof, or units derived from the reaction of a C.sub.6 to C.sub.18 linear aliphatic diacid and of a C.sub.6 to C.sub.18 linear aliphatic diamine, and preferably with the units A and B being respectively based on the diamines x and x′.

6. The composition of claim 5, wherein C is present in a molar content ranging up to 40%.

7. The composition of claim 6, wherein C is in a molar content of less than 40%, relative to the total molar content of the polyamide.

8. The composition of claim 6, wherein A, B and C are respectively 10.T/6.T/11.

9. The composition of claim 1, wherein the ratio of melt viscosity η′.sub.3/η.sub.3 observed at a temperature T.sub.3 is lower than the ratio of melt viscosity η′.sub.2/η.sub.2 observed at a temperature T.sub.2, T.sub.3≥T.sub.2+10° C.

10. The composition of claim 1, wherein the ratio of melt viscosity η′.sub.3/η.sub.3 observed at a temperature T.sub.3 is higher than the ratio of melt viscosity η′.sub.2/η.sub.2 observed at a temperature T.sub.2, T.sub.3≤T.sub.2−10° C.

11. The composition of claim 1, wherein C is present in a molar content ranging up to 30% relative to the total molar content of the polyamide polymer.

12. The composition of claim 1, wherein A is present with a molar content ranging from 55% to 80%, relative to all of the units of said polymer.

13. The composition of claim 1, wherein A and B are selected as follows: when A is 6T, B is selected from: 9T, 10T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, with a molar content of B ranging from 20% to 45%, when A is 9T, B is selected from: 6T, 10T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, with a molar content of B ranging from 30% to 45%, when A is 10T, B is selected from: 6T, 9T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, with a molar content of B ranging from 25% to 45%, when A is 11T, B is selected from: 6T, 9T, 10T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, with a molar content of B ranging from 20% to 45%, and when A is 12T, B is selected from: 6T, 9T, 10T, 11T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, with a molar content of B ranging from 20% to 45%.

14. The composition of claim 13, wherein A is 6T and B is selected from: 9T, 10T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, with a molar content of B ranging from 20% to 45%.

15. The composition of claim 13, wherein A is 9T and B is selected from: 10T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, with a molar content of B ranging from 30% to 45%.

16. The composition of claim 13, wherein A is 10T and B is selected from: 9T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, with a molar content of B ranging from 25% to 45%.

17. The composition of claim 13, wherein A is 11T and B is selected from: 9T, 10T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, with a molar content of B ranging from 20% to 45%.

18. The composition of claim 13, wherein A is 12T and B is selected from: 10T, 11T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, with a molar content of B ranging from 20% to 45%.

19. The composition of claim 1, wherein said reactive polyamide prepolymer has a number-average molecular weight Mn ranging from 500 to 10,000.

20. The composition of claim 1, wherein said reactive polyamide polymer has an average molecular weight which can be modulated according to the temperature to which said polyamide polymer is subjected.

21. The composition of claim 1, wherein said chain extender Y.sub.1-A′-Y.sub.1 is 1,3-phenylene-bis(2-oxazoline) or 1,4-phenylene-bis(2-oxazoline).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0288] FIG. 1 shows the differences in the viscosities of a PA.sub.1 and a PA.sub.1-All.sub.1-PA.sub.1 obtained respectively at T.sub.2 and T.sub.3 starting from a PA.sub.1 and a PA.sub.1-All.sub.1-PA.sub.1 of the same average molecular weight Mn.sub.1 having and exhibiting the same viscosity η.sub.1 at the temperature T.sub.1 greater than or equal to T.sub.m or T.sub.g. It is observed that the viscosity of η′.sub.2 of PA.sub.1-All.sub.1-PA.sub.1 is lower than that (η.sub.2) of PA.sub.1 for the same temperature T.sub.2, greater than T.sub.1, and that the viscosity of η′.sub.3 of PA.sub.1-All.sub.1-PA.sub.1 is lower than that (η.sub.3) of PA.sub.1 for the same temperature T.sub.3 greater than T.sub.1 and that the ratio η′.sub.3/η.sub.3<η′.sub.2/η.sub.2.

[0289] FIG. 2 shows the change in viscosity with the temperature of example E according to the invention and of comparative example CE 1. It is observed that the viscosity of the polymer according to the invention is lower than that of the comparative polymer for T>T.sub.1.

DETAILED DESCRIPTION

Examples

A—Preparation of a Polyamide Polymer by Chain Extension of a Reactive Prepolymer (or Oligomer)

A-1 Preparation of the Reactive Prepolymer P(X.SUB.1.)n

[0290] This procedure is representative of all the types of polyamide of the invention.

[0291] 5 kg of the following starting materials are placed in a 14-liter autoclave reactor: [0292] 500 g of water, [0293] the diamines, [0294] the amino acids or lactams, [0295] the diacids, [0296] 35 g of sodium hypophosphite in solution, [0297] 0.1 g of a Wacker AK1000 antifoam (the company Wacker Silicones).

[0298] The nature and molar ratios of the molecular units and structures of the reactive prepolymer polyamides (by reference test) are given in table 1 below.

[0299] The closed reactor is purged of its residual oxygen and then heated to a temperature of 230° C. of the material. After stirring for 30 minutes under these conditions, the pressurized vapor that has formed in the reactor is gradually reduced in pressure over the course of 60 minutes, while at the same time gradually increasing the temperature of the material such that it becomes established at a minimum of Tm+10° C. at atmospheric pressure for the semicrystalline polymers of Tm>230° C., or 250° C. for the other polymers.

[0300] The oligomer (prepolymer) is then emptied out by the bottom valve and then cooled in a water bath and then ground.

[0301] The characteristics are presented in table 1 below.

TABLE-US-00001 TABLE 1 Characteristics of the prepolymers prepared Molecular Acid Mn structure and Tm Tg Tc ΔH number potentiometry Ref molar composition Monomers used X.sub.1 (° C.) (° C.) (° C.) (J/g) meq/kg(*) g/mol Prepo1 11 Aminoundecanoic acid COOH 178.8 43.2 155 75 809 2472 Adipic acid (1 molecule per chain) Prepo2 11/6T/10T Aminoundecanoic acid COOH 267.8 99 234.5 60 740 2701 (9.1/27.3/63.6) hexamethylenediamine decanediamine terephthalic acid Prepo3 6I/10I hexamethylenediamine COOH (**) 94.5 (**) (**) 900 2222 (30/70) decanediamine isophthalic acid Prepo4 MXDT/10T m-xylylenediamine COOH 270.3 119.4 240.8 50.1 621 3221 (41.2/58.8) decanediamine terephthalic acid (*): Milliequivalents per kilogram (**) Amorphous polymer
A-2 Preparation of the Polyamide Polymer (PA.sub.1-All.sub.1-PA.sub.1) by Chain Extension with an Extender of Y.sub.1-A-Y.sub.1 Type

[0302] 10 g of the dried and ground above prepolymer are mixed with a stoichiometric amount of 1,3-phenylene-bis(2-oxazoline) (PBO). The stoichiometric amount was determined relative to the molar mass determined by NMR.

[0303] The mixture is introduced under nitrogen flushing into a DSM co-rotating conical screw microextruder (15 ml volume) preheated to T.sub.1, as defined in the invention, with rotation of the screws at 100 rpm. The mixture is left to recirculate in the microextruder and the increase in viscosity is monitored by measuring the normal force. After approximately 2 minutes, a plateau is reached and the contents of the microextruder are emptied out in the form of a rod. The air-cooled product is formed into granules.

The characteristics are presented in table 2 below.

TABLE-US-00002 TABLE 2 Analytical characteristics of the polyamides obtained with chain extension (PA.sub.1-All.sub.1-PA.sub.1) Mn 1 (determined by size exclusion chromatography in Pre- T.sub.1 Tm Tg Tc Δ H PMMA equivalent) Ref polymer (° C.) (° C.) (° C.) (° C.) (J/g) (g/mol) E1 According Prepo1 200 174.7 34 142.8 57 28100 to the invention E2 According Prepo2 280 262.7 114 224 46 12600 to the invention E3 According Prepo3 200 (*) 110 (*) (*) 28500 to the invention E4 According Prepo4 280 273 135 230.5 36 9900 to the invention (*) Amorphous polymer

A-3 Preparation of the Comparative Examples PA.SUB.1

[0304] The comparative polyamides free of chain extenders PA.sub.1 are synthesized according to a protocol similar to the reactive prepolymers P(X.sub.1)n: this procedure is representative of all the types of polyamide of the invention.

[0305] The molar mass of the comparative polymer Mn.sub.1 is adjusted according to an excess of diamine or diacid, according to the method well known to those skilled in the art.

[0306] 5 kg of the following starting materials are placed in a 14-liter autoclave reactor: [0307] 500 g of water, [0308] the diamines, [0309] the amino acids or lactams, [0310] the diacids, [0311] 35 g of sodium hypophosphite in solution, [0312] 0.1 g of a Wacker AK1000 antifoam (the company Wacker Silicones).

[0313] The nature and molar ratios of the molecular units and structures of the comparative polyamides (by reference test) are given in table 3 below.

[0314] The closed reactor is purged of its residual oxygen and then heated to a temperature of 230° C. of the material. After stirring for 30 minutes under these conditions, the pressurized vapor that has formed in the reactor is gradually reduced in pressure over the course of 60 minutes, while at the same time gradually increasing the temperature of the material such that it becomes established at a minimum of Tm+10° C. at atmospheric pressure for the semicrystalline polymers of Tm>230° C., or 250° C. for the other polymers.

[0315] The polymer is then emptied out by the bottom valve and then cooled in a water bath and then ground.

[0316] The characteristics are presented in table 3 below.

TABLE-US-00003 TABLE 3 Analytical characteristics of the comparative polyamides free of chain extenders PA.sub.1 Mn 1 (determined by size exclusion Molecular chromatography structure and in PMMA molar Monomers Tm Tg Tc Δ H equivalent) Ref composition used (° C.) (° C.) (° C.) (J/g) (g/mol) CE1 Comparative 11 Aminoundecanoic acid 188.5 47.3 158.4 72.4 28250 (100) Adipic acid (1 molecule per chain) CE2 Comparative 11/6T/10T Aminoundecanoic acid 268.5 114 236 58 12580 (9.1/27.3/63.6) hexamethylenediamine decanediamine terephthalic acid CE3 Comparative 6I/10I hexamethylenediamine (*) 108.3 (*) (*) 28540 (30/70) decanediamine isophthalic acid CE4 Comparative MXDT/10T m-xylylenediamine 279.2 130.7 43.6 241.4 10000 (41.2/58.8) decanediamine terephthalic acid (*) Amorphous polymer

A-4 Comparison of the Viscosities of the PAs According to the Invention and the Comparative PAs

[0317] The viscosities of the polymers according to the invention (PA.sub.1-All.sub.1-PA.sub.1) and of the comparative polyamides free of chain extenders PA.sub.1 are reported in tables 4 to 7 below:

TABLE-US-00004 TABLE 4 Viscosities of tests E1 and CE1 (PA 11) T Viscosity E1 Viscosity CE1 (° C.) (Pa .Math. s) (Pa .Math. s) 200 756.4 751.2 225 128.2 340.6 250 22.51 166.5 275 5.72 86.9 300 1.75 48
These results are represented in FIG. 2.

TABLE-US-00005 TABLE 5 Viscosities of tests E2 and CE2 (PA 11/6T/10T) T Viscosity E2 Viscosity CE2 (° C.) (Pa .Math. s) (Pa .Math. s) 280 188 186 300 49.4 120

TABLE-US-00006 TABLE 6 Viscosities of tests E3 and CE3 (PA 61/101) T Viscosity E3 Viscosity CE3 (° C.) (Pa .Math. s) (Pa .Math. s) 200 42080 42150 250 423 12600

TABLE-US-00007 TABLE 7 Viscosities of tests E4 and CE4 (PA MXDT/10T) T Viscosity E4 Viscosity CE4 (° C.) (Pa .Math. s) (Pa .Math. s) 280 187 189 300 46.2 126
The results clearly show that the melt viscosities of the PAs according to the invention are lower than those of the comparative PAs for temperatures T>T.sub.1.

Embodiments

[0318] 1. A composition, comprising at least one polyamide polymer derived from at least one reactive polyamide prepolymer comprising at least one chain extender (PA.sub.1-All.sub.1-PA.sub.1), said polyamide polymer being prepared at a temperature T.sub.1 greater than or equal to the temperature T.sub.m or T.sub.g of said polymer, determined respectively according to standards ISO 11357-3 and ISO 11357-2, and having an average molecular weight Mn.sub.1, as determined by size exclusion chromatography, [0319] characterized in that said composition has a melt viscosity which can be modulated according to the temperature to which said composition is subjected, [0320] said temperature being included from T.sub.2 to T.sub.3, T.sub.2 and T.sub.3 being greater than T.sub.1, and said melt viscosity η′.sub.2 or η′.sub.3 observed respectively at the temperature T.sub.2 or T.sub.3 being less than the melt viscosity η.sub.2 or η.sub.3 of said polyamide polymer, free of chain extender and having the same average molecular weight Mn.sub.1 (PA.sub.1) observed at the same temperature T.sub.2 or T.sub.3, [0321] and with: [0322] said composition comprising or consisting of one or more polyamides, including random or block copolyamides which are polymers and which comprise different amide units of formula A/(B).sub.r/(C).sub.s, selected as follows: [0323] A: is a repeating amide unit chosen from lactams or an amino acid of C.sub.6-C.sub.14, an amide unit X.Y in which X represents at least one diamine, said diamine being chosen from a linear or branched aliphatic diamine, a cycloaliphatic diamine and an aromatic diamine or a mixture thereof, and Y represents at least one dicarboxylic acid, said diacid being chosen from: [0324] an aliphatic diacid, a cycloaliphatic diacid and an aromatic diacid, [0325] said diamine and said diacid comprising from 4 to 36 carbon atoms, advantageously from 6 to 18 carbon atoms; [0326] B and C: are repeating amide units different than A, optionally present depending on the value of r and s, r=0 or 1, s=0 or 1, said amides units B and C being chosen from the same constituents as for A, on the condition that when r and s=1, then B and C are different, [0327] the sum of the units A+B+C being equal to 100% by weight, [0328] said composition comprising or consisting of a polyamide polymer resulting from the polymerization of the reaction product of: [0329] a1) at least one prepolymer of said thermoplastic polyamide polymer, bearing n reactive end functions X.sub.1, chosen from NH.sub.2 and —CO.sub.2H with n being 1 to 3, preferably from 1 to 2, more preferentially 1 or 2, more particularly 2, with [0330] a2) at least one chain extender Y.sub.1-A′-Y.sub.1, with A′ being a hydrocarbon-based biradical of non-polymeric structure, bearing 2 identical end reactive functions Y.sub.1, reactive by polyaddition with at least one function X of said prepolymer a1), preferably having a molecular weight of less than 500, more preferentially less than 400, [0331] in particular, Y.sub.1 is chosen from: oxazine, oxazoline, oxazolinone, oxazinone, imidazoline, epoxy, maleimide, cyclic anhydride, and preferentially X.sub.1 is CO.sub.2H and Y.sub.1 is chosen from an epoxy and an oxazoline, [0332] said composition being free of reinforcing fibers and also of polymeric chain extender. [0333] 2. The composition as in embodiment 1, characterized in that the ratio of melt viscosity η′.sub.3/η.sub.3 observed at a temperature T.sub.3 is lower than the ratio of melt viscosity η′.sub.2/η.sub.2 observed at a temperature T.sub.2, T.sub.3≥T.sub.2+10° C. [0334] 3. The composition as in embodiment 1, characterized in that the ratio of melt viscosity η′.sub.3/η.sub.3 observed at a temperature T.sub.3 is higher than the ratio of melt viscosity η′.sub.2/η.sub.2 observed at a temperature T.sub.2, T.sub.3≤T.sub.2−10° C. [0335] 4. The composition as in one of embodiments 1 to 3, characterized in that A is an amide unit present in a molar content of 100%, and represents an aliphatic repeating unit obtained from a lactam or an amino acid, in particular chosen from PA6, PA11 and PA12. [0336] 5. The composition as in one of embodiments 1 to 3, characterized in that A is an amide unit present in a molar content of 100%, and represents a repeating amide unit X.Y, in particular chosen from PA6.6, PA6.10, PA6.12, PA10.10 and 10.12. [0337] 6. The composition as in one of embodiments 1 to 5, characterized in that: [0338] A is an amide unit present in a molar content ranging from 1% to 99%, B is an amide unit different than A, said unit B being present in a molar content ranging from 1% to 99%, and C is an optional amide unit different than A and than B and as defined above. [0339] 7. The composition as in embodiment 6, characterized in that: [0340] A: is a major amide unit present in a molar content ranging from 55% to 95%, preferably from 55% to 85%, more preferentially from 55% to 80%, chosen from x.T units, where x is a linear aliphatic C.sub.4 to C.sub.18 diamine, preferably chosen from C.sub.6, C.sub.9, C.sub.10, C.sub.11 and C.sub.12 and where T is terephthalic acid, [0341] B: is an amide unit different than A, said unit B being present in a molar content ranging from 5% to 45%, preferably from 15% to 45%, more preferentially from 20% to 45%, depending on the T.sub.m of the polyamide based on unit A, and said amide unit B is chosen from an aliphatic repeating unit obtained from a lactam or an amino acid, in particular chosen from PA6, PA11 and PA 12 or a repeating amide unit X.Y, in particular chosen from PA6.6, PA6.10, PA6.12, PA10.10 and 10.12. [0342] 8. The composition as in embodiment 6, characterized in that: [0343] A: is a major amide unit present in a molar content ranging from 55% to 95%, preferably from 55% to 85%, more preferentially from 55% to 80%, chosen from x.T units, where x is a linear aliphatic C.sub.4 to C.sub.18 diamine, preferably chosen from C.sub.6, C.sub.9, C.sub.10, C.sub.11 and C.sub.12 and where T is terephthalic acid, [0344] B: is an amide unit different than A, said unit B being present in a molar content ranging from 5% to 45%, preferably from 15% to 45%, more preferentially from 20% to 45%, depending on the T.sub.m of the polyamide based on unit A and said amide unit B is chosen from x′.T units where x′ is chosen from: [0345] B1) a branched aliphatic diamine bearing a single methyl or ethyl branch (or branching) and having a main chain length different by at least two carbon atoms compared with the main chain length of the diamine x of said associated unit A, preferably x′ being 2-methylpentamethylenediamine (MPMD) or [0346] B2) m-xylylenediamine (MXD) or [0347] B3) a linear aliphatic C.sub.4 to C.sub.18 diamine, [0348] and preferably, B being chosen from x′.T, where x′ is MPMD according to B1) or MXD according to B2) or a linear aliphatic diamine as defined above according to B3) and more preferentially x′ is MPMD according to B1) or MXD according to B2) and even more preferentially MXD according to B2), [0349] C: optional amide unit different than A and than B, chosen from amide units based on a cycloaliphatic and/or aromatic structure or based on x′T as defined above for B but with x′ different than x′ for the unit B, [0350] and under the condition that the sum of the molar contents of A+B+C is equal to 100%. [0351] 9. The composition as in one of embodiments 1 to 3 and 6 to 8, characterized in that said amide unit C is present in a molar content ranging up to 30% relative to the total molar content of the polyamide polymer, in particular up to 25%, particularly up to 20%, in particular up to 15%. [0352] 10. The composition as in one of embodiments 1 to 3 and 6 to 8, characterized in that said amide unit A is present with a molar content ranging from 55% to 80%, preferably from 55% to 75%, more preferentially from 55% to 70%, relative to all of the units of said polymer. [0353] 11. The composition as in one of embodiments 1 to 3 and 6 to 8, characterized in that said unit B corresponds to x′ T with x′ chosen according to option B1), in particular with x′ being MPMD. [0354] 12. The composition as in one of embodiments 1 to 3 and 6 to 8, characterized in that said unit B corresponds to x′ T with x′ chosen according to option B2), x′ being MXD. [0355] 13. The composition as in one of embodiments 1 to 3 and 6 to 8, characterized in that said unit B corresponds to a linear aliphatic diamine according to option B3). [0356] 14. The composition as in one of embodiments 1 to 3 and 6 to 8, characterized in that the units A and B are selected as follows: [0357] for the unit A, which is 6T, said unit B is selected from: 9T, 10T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, preferably 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, more preferentially MPMD.T or MXD.T, with a molar content of B ranging from 20% to 45%, [0358] for the unit A, which is 9T, said unit B is selected from: 6T, 10T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, preferably 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, more preferentially MPMD.T or MXD.T, with a molar content of B ranging from 30% to 45%, [0359] for the unit A, which is 10T, said unit B is selected from: 6T, 9T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, preferably 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, more preferentially MPMD.T or MXD.T, with a molar content of B ranging from 25% to 45%, [0360] for the unit A, which is 11T, said unit B is selected from: 6T, 9T, 10T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, preferably 9T, 13T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, more preferentially MPMD.T or MXD.T, with a molar content of B ranging from 20% to 45%, [0361] for the unit A, which is 12T, said unit B is selected from: 6T, 9T, 10T, 11T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, preferably 9T, 10T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, more preferentially MPMD.T or MXD.T, with a molar content of B ranging from 20% to 45%. [0362] 15. The composition as in embodiment 14, characterized in that the unit A is a unit 6T and said unit B is selected from: 9T, 10T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, preferably 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, more preferentially MPMD.T or MXD.T, with a molar content of B ranging from 20% to 45%. [0363] 16. The composition as in embodiment 14, characterized in that the unit A is a unit 9T and the unit B is selected from: 10T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, preferably 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, more preferentially MPMD.T or MXD.T, with a molar content of B ranging from 30% to 45%. [0364] 17. The composition as in embodiment 14, characterized in that the unit A is a unit 10T and the unit B is selected from: 9T, 11T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, preferably 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T, more preferentially MPMD.T or MXD.T and MXD.T, with a molar content of B ranging from 25% to 45%. [0365] 18. The composition as in embodiment 14, characterized in that the unit A is a unit 11T and the unit B is selected from: 9T, 10T, 12T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, preferably 9T, 13T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, more preferentially MPMD.T or MXD.T, with a molar content of B ranging from 20% to 45%. [0366] 19. The composition as in embodiment 14, characterized in that the unit A is a unit 12T and the unit B is selected from: 10T, 11T, 13T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, preferably 9T, 10T, 14T, 15T, 16T, 17T and 18T, MPMD.T and MXD.T, more preferentially MPMD.T or MXD.T, with a molar content of B ranging from 20% to 45%. [0367] 20. The composition as in one of embodiments 1 to 3 and 6 to 8, characterized in that: [0368] the unit A is x.T, x being a C.sub.4 to C.sub.18, preferably C.sub.6, C.sub.9, C.sub.10, C.sub.11 or C.sub.12, linear aliphatic diamine, [0369] the unit B corresponds to x′.T with x′ being B3) a C.sub.4 to C.sub.18 linear aliphatic diamine, and [0370] the unit C is present and in particular chosen from: C.sub.6 to C.sub.12, preferably C.sub.6, C.sub.11 and C.sub.12, amino acids or lactams, or mixtures thereof, or units derived from the reaction of a C.sub.6 to C.sub.18, preferably C.sub.6 to C.sub.12, linear aliphatic diacid and of a C.sub.6 to C.sub.18, preferably C.sub.6 to C.sub.12, linear aliphatic diamine, and preferably with the units A and B being respectively based on the diamines x and x′ as defined in embodiments 1 to 3. [0371] 21. The composition as in embodiment 20, characterized in that said amide unit C is present in a molar content ranging up to 40%. [0372] 22. The composition as in embodiment 21, characterized in that the unit C is in a molar content of less than 40%, in particular less than 30%, in particular less than 20%, relative to the total molar content of the polyamide. [0373] 23. The composition as in embodiment 21 or 22, characterized in that the units A, B and C are respectively 10.T/6.T/11. [0374] 24. The composition as in one of embodiments 1 to 23, characterized in that said reactive prepolymers of said composition a) have a number-average molecular weight Mn ranging from 500 to 10 000, preferably from 1000 to 6000. [0375] 25. The composition as in one of embodiments 1 to 24, characterized in that said polyamide polymer has an average molecular weight which can be modulated according to the temperature to which said polyamide polymer is subjected. [0376] 26. The composition as in one of embodiments 1 to 25, characterized in that said chain extender Y.sub.1-A′-Y.sub.1 is 1,3-phenylene-bis(2-oxazoline) or 1,4-phenylene-bis(2-oxazoline). [0377] 27. A polyamide polymer derived from a polyamide prepolymer comprising a chain extender, as defined in one of embodiments 1 to 26. [0378] 28. The use of at least one polyamide polymer as defined in embodiment 27, for modulating the melt viscosity of a composition comprising said polyamide polymer. [0379] 29. The use as in embodiment 28, for modulating the melt viscosity of a composition comprising said polyamide polymer and the average molecular weight of said polyamide polymer. [0380] 30. The use as in embodiment 28 or 29, characterized in that said chain extender Y.sub.1-A′-Y.sub.1 is chosen from phenylene-bisoxazolines, preferably 1,3-phenylene-bis(2-oxazoline) or 1,4-phenylene-bis(2-oxazoline). [0381] 31. The use of a composition as defined in one of embodiments 1 to 26, for extrusion, injection-molding, or molding for the manufacture of mechanical or structural parts based on a composite material, and in particular for easier impregnation of reinforcing fibers for the manufacture of composite. [0382] 32. The use as in embodiment 31, characterized in that said mechanical or structural parts of said composite material concern applications in the motor vehicle, electrical or electronics, railway, marine (maritime) and wind power fields, the photovoltaic field, the solar energy field, including solar panels and components of solar power stations, the sport field, the aeronautical and aerospace field, and the road transport (regarding trucks), construction, civil engineering, panel and leisure fields. [0383] 33. A process for manufacturing a thermoplastic composite material, in particular a mechanical part or a structural part based on said material, having a composition as defined in one of embodiments 1 to 26, characterized in that it comprises at least one step of molding or of processing at least one composition as defined in embodiments 1 to 26, at a temperature T which makes it possible to obtain a desired viscosity q. [0384] 34. The process as in embodiment 33, characterized in that it comprises the following steps: [0385] i) melt impregnation of a fibrous reinforcement with a composition as defined in one of embodiments 1 to 26 but not comprising fibrous reinforcement, in an open or closed mold or outside the mold, in order to obtain fibers impregnated with said composition, [0386] ii) processing or molding of said composition of step i), so as to form the final composite part in a mold or with another processing system. [0387] 35. The process as in embodiment 34, characterized in that said processing is carried out according to an RTM, S-RIM, injection-compression molding or pultrusion process or by infusion molding. [0388] 36. The process as in embodiment 34, characterized in that said processing is carried out according to a process of thermocompression of a pre-impregnate under reduced pressure. [0389] 37. A thermoplastic composite material, characterized in that it results from the use of at least one composition for thermoplastic composite material as defined in one of embodiments 1 to 26. [0390] 38. A mechanical or structural part made from thermoplastic composite material, characterized in that it results from the use of at least one composition as defined in one of embodiments 1 to 26 or from the use of a polyamide polymer as defined in one of embodiments 28 to 30, or that it is based on a composite material as defined in embodiment 37 or that it is obtained by means of a process as defined in either of embodiments 34 and 35. [0391] 39. The structural part as in embodiment 38, characterized in that it is a motor vehicle part post-treated by cataphoresis. [0392] 40. The part as in embodiment 38, characterized in that it is a part for wind power. [0393] 41. The part as in embodiment 38, characterized in that it is part for the aeronautical industry.