the final polycondensation step when using a conventional stirred reactor is conducted at an external temperature of about 360 u00b0 c and a vacuum of about 70 cm hg the final polycondensation step when using a twin screw extruder as a reactor has good heat conductivity can obtain extensive agitation and provide multi stage heating evacuating and venting during the reaction and thus enables continuous polycondensation in a shorter reaction time and allows these high melting resins to be easily handled the reactive extrusion method is conducted at a temperature of from 240 u00b0 280 u00b0 c and a vacuum of about 60 cm hg the invention will now be described in greater detail with reference to the following non limiting examples a 2 liter reactor fitted with a stirrer was cleaned and purged with nitrogen gas 120 g of hexamethylene diamine hmda was dissolved in a 70 u00b0 c water bath and distilled water was added to the dissolved hmda the amount of the distilled water was 17 percent by weight of the dissolved hmda the mixture was then poured into the reactor and then a suitable amount of adipic acid aa the mole ratio of aa hmda was 1 1 03 and 0 1 percent by weight of sodium hypophosphite was added the reactor was then purged five times with nitrogen gas thereafter the external temperature of the reactor was first set at 230 u00b0 c then raised to 250 u00b0 c after 10 minutes and maintained for 30 minutes and then raised to 280 u00b0 c and maintained for 30 minutes and subsequently raised to 310 u00b0 c and maintained.