Preparation of polytetramethylene adipamide

Claim 1

A process for the preparation of a white, high-molecular-weight nylon 4,6 polyamide, substantially consisting of repeating units of --NH--(CH.sub.2).sub.4 --NH--CO--(CH.sub.2).sub.4 --CO--, which process consists essentially in (a) first forming in a separate first stage a polyamide prepolymer by heating a salt of 1,4-diaminobutane and adipic acid at a temperature between 150° C. and 310° C., wherein said heating within a temperature range of 150° C. to 210° C. is maintained for 15 to 120 minutes, and wherein said heating between 220° C. and 310° C. is minimized, while under a water-vapor-containing atmosphere, wherein the water-vapor partial pressure does not exceed 30 bar, discontinuing said first stage reaction when there has been obtained a polyamide prepolymer having (1) a content of cyclic end groups not exceeding 0.20 mg equivalent per g of prepolymer, and (2) having an η rel of between 1.08 and 2.03 at 1 g of polymer in 100 g of 96% sulfuric acid at 20° C. and thereafter (b) in a separate second stage, after-condensing said polyamide prepolymer, while (1) under a water-vapor-containing atmosphere, (2) and at a temperature of at least 200° C., to obtain a white, high-molecular-weight nylon 4,6 polymer having a η rel of at least 2.20 at 1 g of polymer in 100 g 96% sulfuric acid at 20° C.