Patent ID: 7767782

Claim:
Process for increasing the molecular weight of a polyamide via solid-state post-condensation by exposing the polyamide prepolymer in the solid-state at elevated temperature to an inert gas atmosphere, wherein the process comprises a step (a) wherein the gas atmosphere to which the polyamide is exposed has a dew temperature T dew-1 followed by a step (b) wherein the gas atmosphere to which the polyamide is exposed has a dew temperature T dew-2 , whereby T dew-1 is higher than T dew-2 , and wherein the gas atmosphere of step (a) has a temperature T gas-1 and the gas atmosphere in step (b) has a temperature T gas-2 such that T gas-1 is at least 10° C. higher than T gas-2 , and wherein at the end of step (a), the polyamide has an intermediate-viscosity corresponding with a viscosity number VN int and at the end of step (b) the polyamide polymer has an end-viscosity corresponding with a viscosity number VN end , whereby VN int is at most 90% of VN end , measured according to ISO 307.