Process for producing a polyamide based on a dicarboxylic acid and a diamine

A process for preparing a Polyamide polymer based on a dicarboxylic acid and a diamine by polycondensation in an extruder, which comprises

• (a) heating a mixture of a dicarboxylic acid having from 4 to 12 carbon atoms and a diamine having from 4 to 12 carbon atoms, which mixture is solid at room temperature and has a residual moisture content of less than 5% by weight, to a temperature in the range from 150 to 400° C. under autogenous pressure in a contrarotating twin-screw extruder to give a polyamide product A,
• (b) feeding the polyamide product A to polycondensation in a corotating twin-screw extruder, with the product A being exposed to a temperature in the range from 150 to 400° C. and residual water present and also water from the polycondensation being removed through the degassing openings, to give a polyamide product B, which has a viscosity number (as measured on a 0.5% polymer solution in 96% by weight sulfuric acid at 25° C.) in the range of from 40 to 185 ml/g, with the proviso that the corotating twin-screw extruder has at least two segments having different pressures.