TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The chain extender is 1,3-phenylene-bis(2-oxazoline) or 1,4-phenylene-bis(2-oxazoline).    TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The composition comprises a polyamide polymer derived from the polymerization of the reaction product of: (a1) at least one prepolymer of the thermoplastic polyamide polymer carrying 1-3, preferably 2 reactive terminal functional groups (X11) comprising carboxy (preferred), amino or hydroxy groups; and (a2) at least one chain extender of formula (Y11-A11-Y11) (Ia).A11 = bivalent hydrocarbyl of non-polymeric structure, carrying two terminal identical functional groups Y11 reactive by polyaddition with at least one functional group X11 of the prepolymer (a1), preferably having a molecular weight of less than 500, preferably less than 400; andY11 = oxazoline (preferred), oxazine, oxazolidinone, oxazinone, imidazoline, epoxy, isocyanate, maleimide or cyclic anhydride.Preferred Method: The method comprises: melt impregnation of a fibrous reinforcement with the composition but not comprising fibrous reinforcement in an open or closed mold or outside the mold, to obtain fibers impregnated with the composition; and implementation or molding of the composition to form a final composite part in a mold or with other implementation system. The step of implementation or molding is performed by resin transfer molding, structural reaction injection molding, injection compression, pultrusion or infusion. The step of implementation is performed by a thermocompression of prepreg under reduced pressure. Preferred Components: The viscosity ratio (n13/n3) in molten state observed at a temperature T3 is lower than the viscosity ratio (n12/n2) in molten state observed at temperatures of T2 and T3 which are greater than or equal to the total temperature of T2+10 degrees C. The viscosity ratio (n13/n3) in molten state observed at a temperature T3 is greater than the viscosity ratio (n12/n2) in molten state observed at temperatures of T2 and T3 which are less than or equal to the total temperature of T2-10 degrees C. The amide unit A1 represents an aliphatic repeating unit obtained from a lactam or an amino acid, preferably polyamides PA6, PA11 or PA12, or represents repeating amide units (II), preferably polyamides PA6.6, PA6/10, PA6.12, PA10.10 or PA10.12. The A1 amide units majorly comprise x1x T units, and present at a molar rate of up to 100%, preferably 55-70%, in which x1 is linear aliphatic diamine with 4-18C, preferably 6C, 9C, 10C, 11C or 12C, and T is terephthalic acid. The B1 amide units are different from A1 units and comprise: aliphatic repeating unit obtained from a lactam or an amino acid, preferably polyamides PA6, PA11 or PA12, or repeating amide units (II), preferably polyamides PA6.6, PA6/10, PA6.12, PA10.10 or PA10.12; and x2x T units, and present at a molar rate of 1-99%, preferably 20-45%, based on the melting temperature of the polyamide based on units A1, in which x2 is branched aliphatic diamine carrying a single branch (preferably methyl or ethyl) and having a different main chain with a length of at least two carbon atoms with respect to the length of the main chain of the diamine x1 of the units A1, or a linear aliphatic diamine of 4-18C, preferably 2-methyl pentamethylene diamine, meta-xylylenediamine, or linear aliphatic diamine. The C1 amide units are different from units A1 and B1 and based on a cycloaliphatic and/or aromatic structure, made of x2x T units, where x2 is different from x2 of units B1. The sum of the molar proportions of all the amide units including A1, B1 and C1 is 100%. The amide unit C1 is present at a molar rate of up to 40%, preferably up to 15% relative to the total molar content of the polyamide polymer. The unit A1 is: 6x T, where the unit B1 is 2-methyl pentamethylene diaminex T, meta-xylylenediaminex T (both preferred), 9x T, 10x T, 11x T, 12x T, 13x T, 14x T, 15x T, 16x T, 18x T, 17x T, 18x T, with a molar ratio of unit B1 of 30-45%; 9x T, where the unit B1 is 2-methyl pentamethylene diaminex T, meta-xylylenediaminex T (both preferred), 6x T, 10x T, 11x T, 12x T, 13x T, 14x T, 15x T, 16x T, 18x T, 17x T, 18x T, with a molar ratio of unit B1 of 30-45%; 10x T, where the unit B1 is 2-methyl pentamethylene diaminex T, meta-xylylenediaminex T (both preferred), 6x T, 9x T, 11x T, 12x T, 13x T, 14x T, 15x T, 16x T, 17x T, 18x T, with a molar ratio of unit B1 of 25-45%; 11x T, where the unit B1 is 2-methyl pentamethylene diaminex T, meta-xylylenediaminex T (both preferred), 6x T, 9x T, 10x T, 12x T, 13x T, 14x T, 15x T, 16x T, 17x T, 18x T, with a molar ratio of unit B1 of 20-45%; or 12x T, where the unit B1 is 2-methyl pentamethylene diaminex T, meta-xylylenediaminex T (both preferred), 6x T, 9x T, 10x T, 11x T, 13x T, 14x T, 15x T, 16x T, 17x T, 18x T, with a molar ratio of unit B1 of 20-45%. The C1 amide units are amino acids or lactams with 6-12C, preferably 6C, 11C and/or 12C, and derived from the reaction of a linear aliphatic diacid having 6-18C, preferably 6-12C and a linear aliphatic diamine having 6-18C, preferably 6-12C. The amide units A1, B1 and C1 are 10x T, 6x T and 11, respectively. The reactive prepolymers of the composition have a number average molecular weight of 500-10000, preferably 1000-6000. The polyamide polymer has a number average molecular weight which is adjustable depending on the temperature at which the polyamide polymer is subjected. EXAMPLE - No suitable example given.