Method for producing polyamides

摘要

A method of producing a polyamide having an unreacted caprolactam content of from 0 to 0.5 % by weight and an oligomer content of from 0 to 1.25 % by weight and having a relative viscosity in a 0.01 g/ml solution of sulfuric acid at 25 DEG C of from 2.2 to 8.0, comprises a first step of polymerizing a starting material comprising caprolactam, under atmospheric pressure to prepare a polymerization product having an unreacted caprolactam content of not larger than 25 % by weight and an oligomer content falling between 0 and 1.8 % by weight, and a second step of heating the polymerization product prepared in the first step, at a temperature T satisfying the following formula (1) and under reduced pressure to thereby remove the unreacted caprolactam and the oligomer from it: <MATH>