A composition, comprising at least one polyamide polymer derived from at least one reactive polyamide prepolymer comprising at least one chain extender (PA1-All1-PA1), said polyamide polymer being prepared at a temperature T1 greater than or equal to the temperature Tm or Tg of said polymer, determined respectively according to standards ISO 11357-3 and ISO 11357-2, and having an average molecular weight Mn1, 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 T2 to T3, T2 and T3 being greater than T1,
- and said melt viscosity η′2 or η′3 observed respectively at the temperature T2 or T3 being less than the melt viscosity η2 or η3 of said polyamide polymer, free of chain extender and having the same average molecular weight Mn1 (PA1) observed at the same temperature T2 or T3,
- 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)r/(C)s, selected as follows:
- A is a repeating amide unit chosen from lactams or an amino acid of C6-C14, 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 X1, chosen from NH2 and —CO2H with n being 1 to 3, with
- a2) at least one chain extender Y1-A′-Y1, with A′ being a hydrocarbon-based biradical of non-polymeric structure, bearing 2 identical end reactive functions Y1, reactive by polyaddition with at least one function X of said prepolymer a1),
- Y1 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 C4 to C18 diamine, and wherein T is terephthalic acid,
- B is present in a molar content ranging from 5% to 45%, depending on the Tm 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 C4 to C18 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%.