High molecular weight polyamides and CoPolyamides with uniform RV and low gel content

A method of making a high molecular weight polyamide polymer with a precision Relative Viscosity and low gel content, the method comprising:

• (a) forming and concentrating a nylon salt solution;
• (b) heating the concentrated nylon salt solution in a polycondensation reactor provided with a flasher, thereby to yield a decompressed first polyamide polymer melt maintained at a pressure of about 1 bar, the decompressed first polyamide polymer comprising a first polyamide polymer with a first Relative Viscosity;
• (c) feeding the decompressed first polyamide polymer melt to a finishing vessel that heats the decompressed first polyamide polymer melt under a blanket of inert gas to further polymerize and remove moisture from the decompressed first polyamide polymer melt, thereby to yield a decompressed second polyamide polymer melt comprising a second polyamide polymer with a second Relative Viscosity;
• (d) feeding the decompressed second polyamide polymer melt to a twin screw extruder to melt process the decompressed second polyamide polymer melt under vacuum in the twin screw extruder in the absence of added steam or gas to remove moisture and other volatiles therefrom and to increase a molecular weight of the decompressed second polyamide polymer melt, for a residence time in the twin screw extruder of less than 60 seconds, thereby to yield a third polyamide polymer melt comprising a third polyamide polymer with a third Relative Viscosity, the third polyamide polymer being characterized by either:
• (i) a precision Relative Viscosity greater than 50 as measured in a 90% strength formic acid solution with an RV Standard Deviation of less than or equal to 1.25;
• or
• (ii) a Gel Content Parameter of less than 50 ppm as determined by parts per million insoluble larger than 10 microns in a 90% formic acid solution at 25° C.;
• and
• (e) recovering a product polyamide polymer characterized by either:
• (i) a precision Relative Viscosity greater than 50 as measured in a 90% strength formic acid solution with an RV Standard Deviation of less than or equal to 1.25;
• or (ii) a Gel Content Parameter of less than 50 ppm as determined by parts per million insoluble larger than 10 microns in a 90% formic acid solution at 25° C. and an Average Optical Defect level of less than 2000 ppm as measured by optical scanning at 50 micron resolution.