A composition including at least one polyamide polymer obtained from at least one reactive polyamide prepolymer including at least one chain extender (PA1-All1-PA1), the polyamide polymer being prepared at a temperature T1 no lower than the temperature melting temperature or glass transition temperature of the polymer and having a mean molecular weight Mn1. 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 T2 and T3, T2 and T3 being higher than T1, and the melt viscosity η2 or η′3 observed at the temperature T2 or T3, respectively, being lower than the melt viscosity η2 or η3 of the polyamide polymer, which does not include a chain extender and has the same mean molecular weight Mn1(PA1) observed at the same temperature T2 or T3. The composition includes one or more polyamides.